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  • 101. Farooq, Muhammad
    et al.
    Tao, Zou
    Valle-Delgado, Juan José
    Sipponen, Mika Henrikki
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Morits, Maria
    Österberg, Monika
    Well-Defined Lignin Model Films from Colloidal Lignin Particles2020Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 36, nr 51, s. 15592-15602Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The transformation of a molecularly complex and irregularly shaped lignin into a nanoscale spherical architecture is anticipated to play a pivotal role in the promotion of lignin valorization. From the standpoint of using colloidal lignin particles (CLPs) as building blocks for a diverse range of applications, it has become essential to study their interactions with soluble compounds of varied origin. However, the lack of model films with well-defined surface properties similar to those of CLPs has hindered fundamental studies using surface-sensitive techniques. Here, we report well-defined and stable thin films prepared from CLPs and demonstrate their suitability for investigation of surface phenomena. Direct adsorption on substrates coated with a cationic anchoring polymer resulted in uniform distribution of CLPs as shown with atomic force microscopy (AFM). Quartz crystal microbalance with dissipation monitoring (QCM-D) experiments revealed higher adsorbed mass of cationic lignin onto the CLP-coated substrate in comparison to the film prepared from dissolved lignin, suggesting preferential adsorption via the carboxylic acid enriched surfaces of CLPs. QCM-D further enabled detection of small changes such as particle swelling or partial dissolution not detectable via bulk methods such as light scattering. The CLP thin films remained stable until pH 8 and displayed only a low degree of swelling. Increasing the pH to 10 led to some instability, but their spherical geometry remained intact until complete dissolution was observed at pH 12. Particles prepared from aqueous acetone or aqueous tetrahydrofuran solution followed similar trends regarding adsorption, pH stability, and wetting, although the particle size affected the magnitude of adsorption. Overall, our results present a practical way to prepare well-defined CLP thin films that will be useful not only for fundamental studies but also as a platform for testing stability and interactions of lignin nanoparticles with materials of technical and biomedical relevance.

  • 102. Farzaneh, Amirfarrokh
    et al.
    Zhou, Ming
    Antzutkin, Oleg N.
    Bacsik, Zoltan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Hedlund, Jonas
    Holmgren, Allan
    Grahn, Mattias
    Adsorption of Butanol and Water Vapors in Silicalite-1 Films with a Low Defect Density2016Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 32, nr 45, s. 11789-11798Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Pure silica zeolites are potentially hydrophobic and have therefore been considered to be interesting candidates for separating alcohols, e.g., 1-butanol, from water. Zeolites are traditionally synthesized at high pH, leading to the formation of intracrystalline defects in the form of silanol defects in the framework. These silanol groups introduce polar adsorption sites into the framework, potentially reducing the adsorption selectivity toward alcohols in alcohol/water mixtures. In contrast, zeolites prepared at neutral pH using the fluoride route contain significantly fewer defects. Such crystals should show a much higher butanol/water selectivity than crystals prepared in traditional hydroxide (OH-) media. Moreover, silanol groups ate present at the external surface of the zeolite crystals; therefore, minimizing the external surface of the studied adsorbent is important. In this work, we determine adsorption isotherms of 1-butanol and water in silicalite-1 films prepared in a fluoride (F-) medium using in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. This film was composed of well intergrown, plate-shaped b-oriented crystals, resulting in a low external area. Single-component adsorption isotherms of 1-butanol and water were determined in the temperature range of 35-80 degrees C. The 1-butanol isotherms were typical for an adsorbate showing a high affinity for a microporous material and a large increase in the amount adsorbed at low partial pressures of 1-butanol. The Langmuir-Freundlich model was successfully fitted to the 1-butanol isotherms, and the heat of adsorption was determined. Water showed a very low affinity for the adsorbent, and the amounts adsorbed were very similar to previous reports for large silicalite-1 crystals prepared in a fluoride medium. The sample also adsorbed much less water than did a reference silicalite-1(OH-) film containing a high density of internal defects. The results show that silicalite-1 films prepared in a F- medium with a low density of defects and external area are very promising for the selective recovery of 1-butanol from aqueous solutions.

  • 103. Farzaneh, Amirfarrokh
    et al.
    Zhou, Ming
    Potapova, Elisaveta
    Bacsik, Zoltan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Ohlin, Lindsay
    Holmgren, Allan
    Hedlund, Jonas
    Grahn, Mattias
    Adsorption of Water and Butanol in Silicalite-1 Film Studied with in Situ Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy2015Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 31, nr 17, s. 4887-4894Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Biobutanol produced by, e.g., acetone-butanol-ethanol (ABE) fermentation is a promising alternative to petroleum-based chemicals as, e.g., solvent and fuel. Recovery of butanol from dilute fermentation broths by hydrophobic membranes and adsorbents has been identified as a promising route. In this work, the adsorption of water and butanol vapor in a silicalite-1 film was studied using in situ attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy to better understand the adsorption properties of silicalite-1 membranes and adsorbents. Single-component adsorption isotherms were determined in the temperature range of 35-120 degrees C, and the Langmuir model was successfully fitted to the experimental data. The adsorption of butanol is very favorable compared to that of water. When the silicalite-1 film was exposed to a butanol/water vapor mixture with 15 mol % butanol (which is the vapor composition of an aqueous solution containing 2 wt % butanol, a typical concentration in an ABE fermentation broth, i.e., the composition of the gas obtained from gas stripping of an ABE broth) at 35 degrees C, the adsorption selectivity toward butanol was as high as 107. These results confirm that silicalite-1 quite selectively adsorbs hydrocarbons from vapor mixtures. To the best of our knowledge, this is the first comprehensive study on the adsorption of water and butanol in silicalite-1 from vapor phase.

  • 104. Feng, Dawei
    et al.
    Lei, Ting
    Lukatskaya, Maria R.
    Park, Jihye
    Huang, Zhehao
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Lee, Minah
    Shaw, Leo
    Chen, Shucheng
    Yakovenko, Andrey A.
    Kulkarni, Ambarish
    Xiao, Jianping
    Fredrickson, Kurt
    Tok, Jeffrey B.
    Zou, Xiaodong
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Cui, Yi
    Bao, Zhenan
    Robust and conductive two-dimensional metal-organic frameworks with exceptionally high volumetric and areal capacitance2018Inngår i: Nature Energy, ISSN 2058-7546, Vol. 3, nr 1, s. 30-36Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    For miniaturized capacitive energy storage, volumetric and areal capacitances are more important metrics than gravimetric ones because of the constraints imposed by device volume and chip area. Typically used in commercial supercapacitors, porous carbons, although they provide a stable and reliable performance, lack volumetric performance because of their inherently low density and moderate capacitances. Here we report a high-performing electrode based on conductive hexaaminobenzene (HAB)-derived two-dimensional metal-organic frameworks (MOFs). In addition to possessing a high packing density and hierarchical porous structure, these MOFs also exhibit excellent chemical stability in both acidic and basic aqueous solutions, which is in sharp contrast to conventional MOFs. Submillimetre-thick pellets of HAB MOFs showed high volumetric capacitances up to 760 F cm(-3) and high areal capacitances over 20 F cm(-2). Furthermore, the HAB MOF electrodes exhibited highly reversible redox behaviours and good cycling stability with a capacitance retention of 90% after 12,000 cycles. These promising results demonstrate the potential of using redox-active conductive MOFs in energy-storage applications.

  • 105. Ferreira de Lima, Guilherme
    et al.
    Anderson Duarte, Hélio
    Pettersson, Lars G. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    X-ray Absorption Near-Edge Spectroscopy Calculations on Pristine and Modified Chalcopyrite Surfaces2018Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, nr 35, s. 20200-20209Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Understanding chemical modifications on the chalcopyrite surface is an important issue to improve hydrometallurgical processes to recover copper from the mineral. X-ray absorption near-edge spectroscopy (XANES) can be used for this task, but the interpretation of the spectrum and the correlation with chemical changes in the first atomic layers are not straightforward. The present study demonstrates the potential of combining spectrum measurements with theoretical X-ray spectrum simulations to elucidate the chemistry behind weathering of important classes of minerals. We simulated the S and Fe K-edge XANES spectrum for pristine and modified chalcopyrite surfaces using periodic DFT calculations and the transition-potential model. The calculated S K-edge XANES spectra are in good agreement with experimental data and the peaks were attributed using the density of states. The simulated Fe K-edge XANES spectra do not reproduce all features observed experimentally. The effect of surface changes due to reconstruction, hydration, and oxidation on the spectrum was analyzed. Our results show that the S K-edge XANES spectrum is more sensitive to surface modifications than the Fe K-edge XANES spectrum, and this sensitivity could be used to follow the evolution of the surface.

  • 106.
    Filippov, Stanislav
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Linköping University, Sweden.
    Klarbring, Johan
    Häussermann, Ulrich
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Simak, Sergei I.
    Temperature-induced phase transition and Li self-diffusion in Li2C2: A first-principles study2019Inngår i: Physical Review Materials, E-ISSN 2475-9953, Vol. 3, nr 2, artikkel-id 023602Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Lithium carbide, Li2C2, is a fascinating material that combines strong covalent and weak ionic bonding resulting in a wide range of unusual properties. The mechanism of its phase transition from the ground-state orthorhombic (Immm) to the high-temperature cubic (Fm (3) over barm) crystal structure is not well understood and here we elucidate it with help of first-principles calculations. We show that stabilization of the cubic phase is a result of a temperature-induced disorientation of the C-C dumbbells and their further thermal rotations. Due to these rotations rather large deviatoric stress, which is associated with the dumbbell alignment along one of the crystallographic axes, averages out making the cubic structure mechanically stable. At high temperature we observe a type-II superionic transition to a state of high Li self-diffusion involving collective ionic motion mediated by the formation of Frenkel pairs.

  • 107. Finizio, Simone
    et al.
    Bailey, Joe Bilko
    Olsthoorn, Bart
    Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita).
    Raabe, Jörg
    Periodogram-Based Detection of Unknown Frequencies in Time-Resolved Scanning Transmission X-ray Microscopy2022Inngår i: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 16, nr 12, s. 21071-21078Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Pump–probe time-resolved imaging is a powerful technique that enables the investigation of dynamical processes. Signal-to-noise and sampling rate restrictions normally require that cycles of an excitation are repeated many times with the final signal reconstructed using a reference. However, this approach imposes restrictions on the types of dynamical processes that can be measured, namely, that they are phase locked to a known external signal (e.g., a driven oscillation or impulse). This rules out many interesting processes such as auto-oscillations and spontaneously forming populations, e.g., condensates. In this work we present a method for time-resolved imaging, based on the Schuster periodogram, that allows for the reconstruction of dynamical processes where the intrinsic frequency is not known. In our case we use time of arrival detection of X-ray photons to reconstruct magnetic dynamics without using a priori information on the dynamical frequency. This proof-of-principle demonstration will allow for the extension of pump–probe time-resolved imaging to the important class of processes where the dynamics are not locked to a known external signal and in its presented formulation can be readily adopted for X-ray imaging and also adapted for wider use.

  • 108. Fransson, J.
    et al.
    Thonig, D.
    Bessarab, P. F.
    Bhattacharjee, S.
    Hellsvik, Johan
    Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita).
    Nordstrom, L.
    Microscopic theory for coupled atomistic magnetization and lattice dynamics2017Inngår i: Physical Review Materials, E-ISSN 2475-9953, Vol. 1, nr 7, artikkel-id 074404Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A coupled atomistic spin and lattice dynamics approach is developed which merges the dynamics of these two degrees of freedom into a single set of coupled equations of motion. The underlying microscopic model comprises local exchange interactions between the electron spin and magnetic moment and the local couplings between the electronic charge and lattice displacements. An effective action for the spin and lattice variables is constructed in which the interactions among the spin and lattice components are determined by the underlying electronic structure. In this way, expressions are obtained for the electronically mediated couplings between the spin and lattice degrees of freedom, besides the well known interatomic force constants and spin-spin interactions. These former susceptibilities provide an atomistic ab initio description for the coupled spin and lattice dynamics. It is important to notice that this theory is strictly bilinear in the spin and lattice variables and provides a minimal model for the coupled dynamics of these subsystems and that the two subsystems are treated on the same footing. Questions concerning time-reversal and inversion symmetry are rigorously addressed and it is shown how these aspects are absorbed in the tensor structure of the interaction fields. By means of these results regarding the spin-lattice coupling, simple explanations of ionic dimerization in double-antiferromagnetic materials, as well as charge density waves induced by a nonuniform spin structure, are given. In the final parts, coupled equations of motion for the combined spin and lattice dynamics are constructed, which subsequently can be reduced to a form which is analogous to the Landau-Lifshitz-Gilbert equations for spin dynamics and a damped driven mechanical oscillator for the ionic motion. It is important to notice, however, that these equations comprise contributions that couple these descriptions into one unified formulation. Finally, Kubo-like expressions for the discussed exchanges in terms of integrals over the electronic structure and, moreover, analogous expressions for the damping within and between the subsystems are provided. The proposed formalism and types of couplings enable a step forward in the microscopic first principles modeling of coupled spin and lattice quantities in a consistent format.

  • 109. Gala, Fabrizio
    et al.
    Agosta, Lorenzo
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Zollo, Giuseppe
    Water Kinetics and Clustering on the (101) TiO2 Anatase Surface2016Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, nr 1, s. 450-456Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    (101) anatase TiO2 surface in water ambient is an important system for the interaction of biocompatible nanodevices with biological environment. Following the experimental evidence showing that water molecules are mobile at temperature as low as 190 K and tend to form clusters along the [11 (1) over bar]/[1 (11) over bar] surface directions, a complete theoretical characterization of the dynamical properties of the first water layer on the (101) anatase TiO2 surface is presented. A variety of computational techniques have been employed in the context of the transition-state theory in the harmonic regime, ranging from first-principles total energy ground-state calculations, to density functional perturbation theory, minimum energy path search, and kinetic Monte Carlo simulations, to explain the experimental results on water kinetics on the (101) anatase TiO2 surface. We have calculated the migration energy barrier of water molecules, the vibrational prefactor through the phonon density of states, and the hopping rate along two principal directions. Lastly, in a kinetic Monte Carlo context, we have simulated and clarified the dynamical processes that are on the basis of the observed experimental behavior.

  • 110. Garg, Mohit
    et al.
    Apostolopoulou-Kalkavoura, Varvara
    Linares, Mathieu
    Kaldéus, Tahani
    Malmström, Eva
    Bergström, Lennart
    Zozoulenko, Igor
    Moisture uptake in nanocellulose: The effect of relative humidity, temperature and degree of crystallinityManuskript (preprint) (Annet vitenskapelig)
  • 111. Gebresenbut, Girma
    et al.
    Eklöf, Daniel
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Gordeeva, Alisa
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Shiino, Takayuki
    Häussermann, Ulrich
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Peritectic Formation and Phase Stability of the Icosahedral Quasicystal i-GdCd and Its Ternary Variants with Zn, Mg, and Y2021Inngår i: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 21, nr 6, s. 3355-3363Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Stable binary icosahedral quasicrystals (i-QCs) based on rare earth (RE) and cadmium are typically accessed by solution growth experiments, which operate in very narrow composition and temperature windows. Here, we present a procedure which allows study of peritectic reactions between approximant crystal (AC) phase and liquid yielding i-RECd and exemplify with i-GdCd and ternary variants where Cd is partially replaced by isovalent Zn (i-Gd(Cd,Zn)) or Mg (i-Gd(Cd,Mg)), or the 4f element Gd is replaced by nonmagnetic Y (i-(Gd,Y)Cd). The solubility limits for Zn and Mg substitution are about 10% and 20%, respectively, whereas Gd and Y show a complete solid solution behavior. We find that the peritectic decomposition temperature for i-GdCd is 390 degrees C, which is decreased when Gd is replaced by Y (i-YCd: 350 degrees C) and increased when Cd is replaced by Zn (i-Gd(Cd90Zn10): 440 degrees C), and especially by Mg (i-Gd(Cd80Mg20): 520 degrees C). Whereas substitution decisively alters the decomposition temperature (and hence stability) of the considered i-QCs, the decomposition temperature of the corresponding AC phases remains at around 700 degrees C. During the investigation of the pseudobinary phase diagrams Gd-(Cd95Zn5), Gd-(Cd90Zn10), and Gd-(Cd(80M)g(20)), faceted i-QCs grains with sizes up to 4 x 4 x 4 mm(3) could be isolated.

  • 112.
    Geilhufe, R. Matthias
    et al.
    Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita).
    Commeau, Benjamin
    Fernando, Gayanath W.
    Chemical-Strain Induced Tilted Dirac Nodes in (BEDT-TTF)(2)X-3 (X = I, Cl, Br, F) Based Charge-Transfer Salts2018Inngår i: Physica Status Solidi. Rapid Research Letters, ISSN 1862-6254, E-ISSN 1862-6270, Vol. 12, nr 11, artikkel-id 1800081Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The identification of novel multifunctional Dirac materials has been an ongoing effort. In this connection quasi 2-dimensional (BEDT-TTF)-based charge transfer salts are widely discussed. Here, we report about the electronic structure of alpha-(BEDT-TTF)(2)I-3 and kappa-(BEDT-TTF)(2)I-3 under a hypothetical substitution of iodine with the halogens bromine, chlorine, and fluorine. The decreasing size of the anion layer corresponds to applying chemical strain which increases tremendously in the case of (BEDT-TTF)(2)F-3. We perform structural optimization and electronic structure calculations in the framework of density functional theory, incorporating, first, the recently developed strongly constrained and appropriately normed semilocal density functional SCAN, and, second, van der Waals corrections to the PBE exchange correlation functional by means of the dDsC dispersion correction method. In the case of alpha-(BEDT-TTF)(2)F-3, the formation of over-tilted Dirac-type-II nodes within the quasi two-dimensional Brillouin zone can be found. For kappa-(BEDT-TTF)(2)F-3, the recently reported topological transition within the electronic band structure cannot be revealed.

  • 113.
    Geilhufe, R. Matthias
    et al.
    Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita).
    Guinea, Francisco
    Juričić, Vladimir
    Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita).
    Hund nodal line semimetals: The case of a twisted magnetic phase in the double-exchange model2019Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, nr 2, artikkel-id 020404Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We propose a class of topological metals, which we dub Hund nodal line semimetals, arising from the strong Coulomb interaction encoded in the Hund's coupling between itinerant electrons and localized spins. We here consider a particular twisted spin configuration, which is realized in the double-exchange model which describes the manganite oxides. The resulting effective tetragonal lattice of electrons with hoppings tied to the local spin features an antiunitary nonsymmorphic symmetry that, in turn, together with another nonsymmorphic but unitary glide-mirror symmetry, protects crossings of a double pair of bands along a high-symmetry line on the Brillouin zone boundary. We also discuss the stability of Hund nodal line semimetals with respect to symmetry breaking arising from various perturbations of the twisted phase. Our results motivate further studies of other realizations of this state of matter, for instance, in different spin backgrounds, properties of its drumhead surface states, as well as its stability to disorder and interactions among the itinerant electrons.

  • 114.
    Geilhufe, R. Matthias
    et al.
    Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita).
    Olsthoorn, Bart
    Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita).
    Identification of strongly interacting organic semimetals2020Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 102, nr 20, artikkel-id 205134Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Dirac and Weyl point- and line-node semimetals are characterized by a zero band gap with simultaneously vanishing density of states. Given a sufficient interaction strength, such materials can undergo an interaction instability, e.g., into an excitonic insulator phase. Due to generically flatbands, organic crystals represent a promising materials class in this regard. We combine machine learning, density functional theory, and effective models to identify specific example materials. Without taking into account the effect of many-body interactions, we found the organic charge transfer salts [bis(3,4-diiodo-3',4'-ethyleneditio-tetrathiafulvalene), 2,3-dichloro-5,6-dicyanobenzoquinone, acetenitrile] [(EDT-TTF-I-2)(2)](DDQ)center dot(CH3CN) and 2, 2', 5, 5'-tetraselenafulvalene-7, 7, 8, 8-tetracyano-p-quinodimethane (TSeF-TCNQ) and a bis-1,2,3-dithiazolyl radical conductor to exhibit a semimetallic phase in our ab initio calculations. Adding the effect of strong particle-hole interactions for (EDT-TTF-I-2)(2)(DDQ)center dot(CH3CN) and TSeF-TCNQ opens an excitonic gap on the order of 60 and 100 meV, which is in good agreement with previous experiments on these materials.

  • 115.
    Geilhufe, R. Matthias
    et al.
    Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita).
    Olsthoorn, Bart
    Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita).
    Ferella, Alfredo D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Koski, Timo
    Kahlhoefer, Felix
    Conrad, Jan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Balatsky, Alexander V.
    Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita). University of Connecticut, USA; Los Alamos National Laboratory, USA.
    Materials Informatics for Dark Matter Detection2018Inngår i: Physica Status Solidi. Rapid Research Letters, ISSN 1862-6254, E-ISSN 1862-6270, Vol. 12, nr 11, artikkel-id 1800293Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Dark Matter particles are commonly assumed to be weakly interacting massive particles (WIMPs) with a mass in the GeV to TeV range. However, recent interest has shifted toward lighter WIMPs, which are more difficult to probe experimentally. A detection of sub-GeV WIMPs will require the use of small gap materials in sensors. Using recent estimates of the WIMP mass, we identify the relevant target space toward small gap materials (100 to 10 meV). Dirac Materials, a class of small- or zero-gap materials, emerge as natural candidates for sensors for Dark Matter detection. We propose the use of informatics tools to rapidly assay materials band structures to search for small gap semiconductors and semimetals, rather than focusing on a few preselected compounds. As a specific example of the proposed strategy, we use the organic materials database () to identify organic candidates for sensors: the narrow band gap semiconductors BNQ-TTF and DEBTTT with gaps of 40 and 38 meV, and the Dirac-line semimetal (BEDT-TTF)center dot Br which exhibits a tiny gap of approximate to 50 meV when spin-orbit coupling is included. We outline a novel and powerful approach to search for dark matter detection sensor materials by means of a rapid assay of materials using informatics tools.

  • 116. Goetz, Lee A.
    et al.
    Naseri, Narges
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Nair, Santhosh S.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Karim, Zoheb
    Mathew, Aji P.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Luleå University of Technology, Sweden.
    All cellulose electrospun water purification membranes nanotextured using cellulose nanocrystals2018Inngår i: Cellulose, ISSN 0969-0239, E-ISSN 1572-882X, Vol. 25, nr 5, s. 3011-3023Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cellulose acetate (CA) fibers were electrospun on a mesh template to create specific surface and pore structures for membrane applications. The mesh template CA fiber mats were impregnated with cellulose nanocrystals at varying weight percentages. The membranes showed nanotextured surfaces and improved mechanical properties post impregnation. More importantly, the hydrophilicity of the original CA fibers was increased from a hydrophobic contact angle of 102 degrees-0 degrees thereby creating an anti-fouling membrane surface structure. The membranes showed rejection of 20-56% for particles of 0.5-2.0 mu m, indicating potential of these membranes in rejecting microorganisms from water. Furthermore, high rejection of dyes (80-99%) by adsorption and potential application as highly functional affinity membranes was demonstrated. These membranes can therefore be utilized as all-cellulose, green, scalable and low cost high flux membranes (> 20,000 LMH) for water cleaning applications in food industry where microorganisms and charged contaminants are to be removed.

  • 117.
    Golod, Taras
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Pagliero, Alessandro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Krasnov, Vladimir M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. State University, Russia.
    Two mechanisms of Josephson phase shift generation by an Abrikosov vortex2019Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, nr 17, artikkel-id 174511Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Abrikosov vortices contain magnetic fields and circulating currents that decay at a short range λ∼100 nm. However, vortices can induce Josephson phase shifts at a long range r∼μm≫λ. Mechanisms of this puzzling phenomenon are not clearly understood. Here we present a systematic study of vortex-induced phase shifts in planar Josephson junctions. We make two key observations: (i) The cutoff effect: Although vortex-induced phase shift is a long-range phenomenon, it is terminated by the junction and does not persist beyond it. (ii) A linear to superlinear crossover with a rapid upturn of the phase shift occurs upon approaching a vortex to a junction. The crossover occurs at a vortex-junction distance comparable to the penetration depth. Together with theoretical and numerical analysis this allows unambiguous identification of two distinct and independent mechanisms. The short range r≲λ mechanism is due to circulating vortex currents inside a superconducting electrode without involvement of magnetic fields. The long range r≫λ mechanism is due to stray magnetic fields outside electrodes without circulating vortex currents. We argue that understanding of controlling parameters of vortex-induced Josephson phase shift can be used for development of novel compact cryoelectronic devices.

  • 118. Gong, Jiang
    et al.
    Zhang, Jinshui
    Lin, Huijuan
    Yuan, Jiayin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Clarkson University, USA.
    Cooking carbon in a solid salt: Synthesis of porous heteroatom-doped carbon foams for enhanced organic pollutant degradation under visible light2018Inngår i: Applied Materials Today, ISSN 2352-9407, Vol. 12, s. 168-176Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Porous heteroatom-doped carbons are desirable for catalytic reactions due to their tunable physicochemical properties, low cost and metal-free nature. Herein, we introduce a facile, general bottom-up strategy, so-called cooking carbon in a solid salt, to prepare hierarchically porous heteroatom-doped carbon foams by using poly(ionic liquid) as precursor and a common inorganic salt as structural template. The obtained carbon foams bear hierarchical micro-/meso-/macropores, large specific surface area and rich nitrogen dopant. The combination of these favorable features facilitates the catalytic degradation of aqueous organic pollutants by persulfate under visible light irradiation, in which they prevail over the state-of-the-art metal-/carbon-based catalysts.

  • 119. Greco, Gabriele
    et al.
    Arndt, Tina
    Schmuck, Benjamin
    Francis, Juanita
    Bäcklund, Fredrik G.
    Shilkova, Olga
    Barth, Andreas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Gonska, Nathalie
    Seisenbaeva, Gulaim
    Kessler, Vadim
    Johansson, Jan
    Pugno, Nicola M.
    Rising, Anna
    Tyrosine residues mediate supercontraction in biomimetic spider silk2021Inngår i: Communications materials, ISSN 2662-4443, Vol. 2, nr 1, artikkel-id 43Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Exposing spider silk to wet conditions can cause supercontraction. Here, tyrosine amino acid residues within the amorphous regions are found to contribute to supercontraction, which can be controlled by protein engineering. Water and humidity severely affect the material properties of spider major ampullate silk, causing the fiber to become plasticized, contract, swell and undergo torsion. Several amino acid residue types have been proposed to be involved in this process, but the complex composition of the native fiber complicates detailed investigations. Here, we observe supercontraction in biomimetically produced artificial spider silk fibers composed of defined proteins. We found experimental evidence that proline is not the sole residue responsible for supercontraction and that tyrosine residues in the amorphous regions of the silk fiber play an important role. Furthermore, we show that the response of artificial silk fibers to humidity can be tuned, which is important for the development of materials for applications in wet environments, eg producing water resistant fibers with maximal strain at break and toughness modulus.

  • 120. Grigorev, Vladimir
    et al.
    Filianina, Mariia
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Johannes Gutenberg University, Germany; Graduate School of Excellence Materials Science in Mainz, Germany.
    Lytvynenko, Yaryna
    Sobolev, Sergei
    Pokharel, Amrit Raj
    Lanz, Amon P.
    Sapozhnik, Alexey
    Kleibert, Armin
    Bodnar, Stanislav
    Grigorev, Petr
    Skourski, Yurii
    Klaeui, Mathias
    Elmers, Hans-Joachim
    Jourdan, Martin
    Demsar, Jure
    Optically Triggered Néel Vector Manipulation of a Metallic Antiferromagnet Mn2Au under Strain2022Inngår i: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 16, nr 12, s. 20589-20597Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The absence of stray fields, their insensitivity to external magnetic fields, and ultrafast dynamics make antiferromagnets promising candidates for active elements in spintronic devices. Here, we demonstrate manipulation of the Néel vector in the metallic collinear antiferromagnet Mn2Au by combining strain and femtosecond laser excitation. Applying tensile strain along either of the two in-plane easy axes and locally exciting the sample by a train of femtosecond pulses, we align the Néel vector along the direction controlled by the applied strain. The dependence on the laser fluence and strain suggests the alignment is a result of optically triggered depinning of 90° domain walls and their motion in the direction of the free energy gradient, governed by the magneto-elastic coupling. The resulting, switchable state is stable at room temperature and insensitive to magnetic fields. Such an approach may provide ways to realize robust high-density memory device with switching time scales in the picosecond range. 

  • 121.
    Grins, Jekabs
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Wardecki, Dariusz
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). University of Warsaw, Poland; Chalmers University of Technology, Sweden.
    Jansson, Kjell
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Carlson, Stefan
    Biendicho, Jordi J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Catalonia Institute for Energy Research, Spain.
    Svensson, Gunnar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    A structural study of Ruddlesden-Popper phases Sr3-xYx(Fe1.25Ni0.75)O7-delta with x <= 0.75 by neutron powder diffraction and EXAFS/XANES spectroscopy2018Inngår i: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 6, nr 13, s. 5313-5323Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The structures of Ruddlesden-Popper n = 2 member phases Sr3-xYxFe1.25Ni0.75O7-delta with 0 <= x <= 0.75 have been investigated using neutron powder diffraction and K-edge Fe and Ni EXAFS/XANES spectroscopy in order to gain information about the evolution of the oxygen vacancy distribution and Fe/Ni oxidation state with x. Both samples prepared at 1300 degrees C under a flow of N-2(g), with delta = 1.41-1.00, and samples subsequently annealed in air at 900 degrees C, with delta = 0.44-0.59, were characterized. The as-prepared x = 0.75 phase has delta = 1, the O1 atom site is vacant, and the Fe3+/Ni2+ ions have a square pyramidal coordination. With decreasing x the O3 occupancy decreases nearly linearly to 81% for x = 0, while the O1 occupancy increases from 0 for x = 0.4 to 33% for x = 0. The air-annealed x = 0.75 sample has a delta value of 0.59 and the Fe3+/Fe4+/Ni2+/Ni3+ ions have both square pyramidal and octahedral coordination. With decreasing x, the delta value decreases to 0.45 for x = 0, implying an increase in the oxidation states of Fe/Ni ions. EXAFS/XANES data show that for the as-prepared samples the coordination changes are predominantly for Ni2+ ions and that the air-annealed samples contain both Fe3+/Fe4+ and Ni2+/Ni3+ ions.

  • 122.
    Guo, Hua
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Peking University, People's Republic of China. .
    Ping, He
    Hu, Jiangtao
    Song, Xiaohe
    Zheng, Jiaxin
    Pan, Feng
    Controllable synthesis of LiFePO4 in different polymorphs and study of the reaction mechanism2017Inngår i: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 5, nr 27, s. 14294-14300Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Lithium iron phosphate, a widely used cathode material in Lithium Ion Batteries (LIBs), crystallizes typically in an olivine-type phase, alpha-LiFePO4 (aLFP). However, the new phase beta-LiFePO4 (bLFP), which can be transformed from aLFP at high temperature with high pressure, can be produced through a simple liquid-phase reaction. The mechanism of controllable synthesis of the two polymorphs of lithium iron phosphate has not been studied thoroughly. In this paper, with thorough experiments, we demonstrate that controllable synthesis of LFP with different crystal polymorphs can be obtained by controlling certain conditions. The phosphoric acid ratio in the reactants and the reaction time play key roles in the controllable syntheses. Higher phosphoric acid ratios and shorter reaction times would result in a higher bLFP content, while a lower amount of phosphoric acid and a longer reaction time would be beneficial to aLFP formation. To illustrate the mechanism for this phenomenon, the detailed reaction process was researched via X-ray diffraction, from which a possible mechanism associated with the evolution of crystal structures was demonstrated. The solvent content is also important for the process: some water content would lead to nanoplate-shaped aLFP particles appearing. Their influence on the reaction could be attributed to the change of thermodynamics and kinetics, which leads to different crystal nucleation, growth and phase-change processes.

  • 123.
    Guo, Peng
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Dalian Institute of Chemical Physics, Chinese Academy of Sciences, P. R. China.
    Yan, Nana
    Wang, Lei
    Zou, Xiaodong
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Database Mining of Zeolite Structures2017Inngår i: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 17, nr 12, s. 6821-6835Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Zeolites are widely used in industrial applications such as ion exchange, gas separation and adsorption, and organic catalysis. In particular, in petroleum refining and petrochemical productions, zeolites are catalysts of utmost importance. In order to classify the known zeolites and correlate the structures with their unique properties, an online Database of Zeolite Structures was established in 1996 and continuously developed by Baerlocher and McCusker at ETH-Zurich. The database contains a lot of useful structural information such as unit cell dimensions, space group, atomic coordinates of tetrahedra (T) atoms, secondary building units (SBUs), composite building units (CBUs), natural tilings, simulated powder X-ray diffraction (PXRD), etc. It has served the zeolite community for more than 20 years and has made great contributions to the development of zeolites and zeolite-related fields. In this article, we take a further step to mine the intrinsic structural information on zeolites including characteristic unit cell dimensions, butterfly layers, zeolites containing the same building layers, ABC-6 zeolite family, and recently discovered embedded isoreticular RHO family. The database mining of zeolite structures will shed light not only on structural correlations of related existing zeolites but also the structure determination and the further prediction of novel zeolite structures based on the existing ones, which will facilitate the target synthesis of energetically feasible hypothetical zeolite structures.

  • 124. Görlin, Mikaela
    et al.
    Ojwang, Dickson O.
    Lee, Ming-Tao
    Renman, Viktor
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Valvo, Mario
    Aging and Charge Compensation Effects of the Rechargeable Aqueous Zinc/Copper Hexacyanoferrate Battery Elucidated Using In Situ X-ray Techniques2021Inngår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 13, nr 50, s. 59962-59974Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The zinc/copper hexacyanoferrate (Zn/CuHCF) cell has gained attention as an aqueous rechargeable zinc-ion battery (ZIB) owing to its open framework, excellent rate capability, and high safety. However, both the Zn anode and the CuHCF cathode show unavoidable signs of aging during cycling, though the underlying mechanisms have remained somewhat ambiguous. Here, we present an in-depth study of the CuHCF cathode by employing various X-ray spectroscopic techniques. This allows us to distinguish between structure-related aging effects and charge compensation processes associated with electroactive metal centers upon Zn2+ ion insertion/deinsertion. By combining high-angle annular dark-field-scanning electron transmission microscopy, X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy, and elemental analysis, we reconstruct the picture of both the bulk and the surface. First, we identify a set of previously debated X-ray diffraction peaks appearing at early stages of cycling (below 200 cycles) in CuHCF. Our data suggest that these peaks are unrelated to hypothetical ZnxCu1–xHCF phases or to oxidic phases, but are caused by partial intercalation of ZnSO4 into graphitic carbon. We further conclude that Cu is the unstable species during aging, whose dissolution is significant at the surface of the CuHCF particles. This triggers Zn2+ ions to enter newly formed Cu vacancies, in addition to native Fe vacancies already present in the bulk, which causes a reduction of nearby metal sites. This is distinct from the charge compensation process where both the Cu2+/Cu+ and Fe3+/Fe2+ redox couples participate throughout the bulk. By tracking the K-edge fluorescence using operando XAS coupled with cyclic voltammetry, we successfully link the aging effect to the activation of the Fe3+/Fe2+ redox couple as a consequence of Cu dissolution. This explains the progressive increase in the voltage of the charge/discharge plateaus upon repeated cycling. We also find that SO42– anions reversibly insert into CuHCF during charge. Our work clarifies several intriguing structural and redox-mediated aging mechanisms in the CuHCF cathode and pinpoints parameters that correlate with the performance, which will hold importance for the development of future Prussian blue analogue-type cathodes for aqueous rechargeable ZIBs.

  • 125. Gözcü, Oğuz
    et al.
    Kayacı, H. Utkucan
    Dou, Yibo
    Zhang, Wenjing
    Hedin, Niklas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Jasso-Salcedo, Alma Berenice
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Kaiser, Andreas
    Çınar Aygün, Simge
    Colloidal Stabilization of Submicron-Sized Zeolite NaA in Ethanol–Water Mixtures for Nanostructuring into Thin Films and Nanofibers2023Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 39, nr 1, s. 192-203Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Despite the growing use of organic or mixed solvents in zeolite processing, most studies focus only on aqueous suspension systems. We investigated the colloidal characteristics of submicron-sized zeolite NaA in mixed ethanol–water solvents. The effects of the mixing ratio of solvents and various additives on the dispersion of the zeolite powders were studied. The zeolite NaA particles were destabilized in solvent mixtures at a high ethanol-to-water ratio, a reduction in the zeta potential was observed, and the destabilization was rationalized by the Derjaguin, Landau, Verwey, Overbeek (DLVO) theory. An improved stabilization of the zeolite NaA suspensions was achieved in ethanol-rich solvent mixtures using nonionic low molecular weight organic additives, but not with their ionic counterparts such as anionic, cationic surfactants or inorganic acids or bases. Polyethylene glycol (PEG)-400 was found to be a good dispersant for the submicron-sized zeolite NaA particles in the ethanol–water mixtures, which was attributed to its interaction with the zeolite surface, leading to an increased zeta potential. The PEG-stabilized zeolite suspensions led to low suspension viscosities as well as uniform and consistent spin-coated films. 

  • 126.
    Hadi, Seyed Ehsan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Colloidal Processing and Alignment of Wood-Based Dispersions and Hybrid Functional Foams2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis presents novel methods and approaches for designing, preparing/fabricating, and characterizing wood-based nanomaterials. It investigates how modifications in structure, process variables, and composition can enhance functional properties. It employs advanced characterization techniques to analyze process-structure-property relationships and utilizes innovative colloidal processing approaches such as controlled nanoparticle incorporation, Layer-by-Layer self-assembly, and unidirectional ice-templating to improve the functional properties of wood-based nanomaterials.

    A novel approach has been developed to fabricate lightweight, highly porous hybrid foams using iron oxide nanoparticles (IONP) and TEMPO-oxidized cellulose nanofibers (TOCNF). The addition of tannic acid (TA) and the application of a magnetic field-enhanced unidirectional ice-templating technique (MFUIT) enhanced processability, mechanical, and magnetic characteristics of the foams. The hybrid foam containing 87% IONPs exhibited a saturation magnetization of 83.2 emu g–1, which is equivalent to 95% of the magnetization value observed in bulk magnetite.

    Hybrid, anisotropic foams have been prepared by incorporation of reduced graphene oxide (rGO) onto the macropore-walls of anisotropic TOCNF foams using a liquid-phase Layer-by-Layer self-assembly method. These hierarchical rGO-TOCNF foams exhibit lower radial thermal conductivity (λr) across a wide range of relative humidity compared to control TOCNF foams.

    The shear-induced orientations and relaxations of multi-component dispersions containing cellulose nanocrystals (CNC) and montmorillonite nanoplatelets (MNT) have been studied by rheological small-angle X-ray scattering (Rheo-SAXS). The addition of MNT resulted in gelation and changes in flow behavior, shear responses, and relaxation dynamics. Rheo-SAXS measurements showed that CNC and MNT aligned under shear, creating aligned structures that relaxed upon shear removal. Gaining insights into shear-induced orientations and relaxation dynamics can aid in the development of advanced wood-based nanocomposite materials.

    Transmission Electron Microscopy (TEM) was employed to characterize lignin oleate nanoparticles (OLNPs) derived from abundant lignin waste. TEM analysis revealed that the OLNPs had a spherical shape and a core-shell structure. Upon drying, the particles tended to agglomerate due to the loss of electrostatic repulsion forces. This agglomeration behavior indirectly supports the hypothesis that oleate chains act as a hydration barrier, preventing water permeation into the particles. 

    Finally, a comprehensive study showed that TEMPO-oxidized lignocellulose nanofibers (TOLCNF)-based foams made from unbleached pulp can be used to prepare anisotropic, light-weight ice-templated foams with high mechanical strength. TOLCNF foams utilize lignin and hemicellulose to enhance properties while require less energy for production compared to TOCNF-based foams. This study emphasizes the potential for developing sustainable wood-based nanomaterials using TOLCNF.

    The results presented in this thesis offer valuable insights for further advancements of wood-based nanomaterials. 

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  • 127.
    Hadi, Seyed Ehsan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Davoodi, Saeed
    Oliaei, Erfan
    Morsali, Mohammad
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Åhl, Agnes
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Nocerino, Elisabetta
    Wang, Fengyang
    Andersson, Matilda
    Lühder, Malwine
    Conceição, André L. C
    Sipponen, Mika H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för materialkemi.
    Berglund, Lars A.
    Bergström, Lennart
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för materialkemi. Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för oorganisk kemi och strukturkemi.
    Lundell, Fredrik
    Comparing the production energy, structure and properties of TEMPO-Oxidized Lignocellulose and Cellulose Nanofibers FoamsManuskript (preprint) (Annet (populærvitenskap, debatt, mm))
  • 128. Hafiz, Hasnain
    et al.
    Khair, Adnan Ibne
    Choi, Hongchul
    Mueen, Abdullah
    Bansil, Arun
    Eidenbenz, Stephan
    Wills, John
    Zhu, Jian-Xin
    Balatsky, Alexander V.
    Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita). University of Connecticut, USA.
    Ahmed, Towfiq
    A high-throughput data analysis and materials discovery tool for strongly correlated materials2018Inngår i: npj Computational Materials, E-ISSN 2057-3960, Vol. 4, artikkel-id 63Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Modeling of f-electron systems is challenging due to the complex interplay of the effects of spin-orbit coupling, electron-electron interactions, and the hybridization of the localized f-electrons with itinerant conduction electrons. This complexity drives not only the richness of electronic properties but also makes these materials suitable for diverse technological applications. In this context, we propose and implement a data-driven approach to aid the materials discovery process. By deploying state-of-the-art algorithms and query tools, we train our learning models using a large, simulated dataset based on existing actinide and lanthanide compounds. The machine-learned models so obtained can then be used to search for new classes of stable materials with desired electronic and physical properties. We discuss the basic structure of our f-electron database, and our approach towards cleaning and correcting the structure data files. Illustrative examples of the applications of our database include successful prediction of stable superstructures of double perovskites and identification of a number of physically-relevant trends in strongly correlated features of f-electron based materials.

  • 129.
    Halldin Stenlid, Joakim
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Campos Dos Santos, Egon
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Universidade Federal de Minas Gerais, Brasil.
    Bagger, Alexander
    Johansson, Adam Johannes
    Rossmeisl, Jan
    Pettersson, Lars G. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Electrochemical Interface during Corrosion of Copper in Anoxic Sulfide-Containing Groundwater-A Computational Study2020Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 124, nr 1, s. 469-481Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Corrosion of copper is an expensive degradation process of materials in engineered infrastructures and in various technical applications. It is also an important factor in the geological disposal of spent nuclear fuel, where sulfide-induced corrosion is expected to be the predominant chemical degradation process of copper canisters used for encapsulation and isolation of the radioactive material from the biosphere. One aspect of the corrosion process that is still under intense research is the corrosion morphology and how it might be affected by the composition of the groundwater. Using density functional theory, we investigate the electrochemical interface of corroding copper in aqueous solutions containing sulfides, with and without the presence of Cl-, HCO3-, and SO42- anions. Through state-of-the-art electrochemical models, we account for the effects of pH, concentrations, and potential on the interfacial structure and composition. Results are presented for the Cu(110) surface facet and compared to the (110) and (001) facets of chalcocite (Cu2S), i.e., the main product of sulfide-induced corrosion. It is found that at low potentials, H dominates on all surfaces, and at high potentials, sulfides. In the intermediate ranges, the surfaces differ with sulfides prevailing on Cu, while adsorbed H2O, Cl, or H dominate on Cu2S. The results are summarized as surface Pourbaix diagrams and are generally applicable in corrosion science and electrochemistry. The implications of the study are discussed in light of the expected conditions of planned spent nuclear fuel repositories in Sweden, Finland, and Canada.

  • 130.
    Halldin Stenlid, Joakim
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Campos dos Santos, Egon
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Universidade Federal de Minas Gerais, Brazil.
    Johansson, Adam Johannes
    Pettersson, Lars G. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    On the Nature of the Cathodic Reaction during Corrosion of Copper in Anoxic Sulfide Solutions2019Inngår i: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 166, nr 6, s. C196-C208Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Sulfide-induced corrosion is expected to be the dominating long-term corrosion process for copper containers in technical concepts for deep geological disposal of spent nuclear fuel (SNF), adapted in several waste management programs around the world. The present study investigates the atomic-scale mechanism of the cathode side of the corrosion reaction using Density Functional Theory (DFT) calculations. Despite the central role of the reaction, neither the site of reaction nor the active species has been previously established. Here we compare the cathodic reaction leading to H-2-evolution on pure copper and on chalcocite (Cu2S) surfaces. The considered H-donors are OH-/H2O and HS-/H2S which are all available at the neutral to alkaline conditions anticipated at the SNF disposal sites. Assuming Volmer-Tafel-Heyrovsky kinetics, we find that the cathodic reactions are many orders of magnitude faster on copper compared to copper sulfide. Although we find that HS-/H2S have lower reaction barriers than H2O, our kinetic analysis suggest that H2O is expected to be the main H-source for the cathodic reaction under SNF repository conditions as results of the low sulfide concentrations (less than or similar to 10 mu M) expected in SNF repositories in Sweden, Finland and Canada.

  • 131.
    Halldin Stenlid, Joakim
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Campos dos Santos, Egon
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Universidade Federal de Minas Gerais, Brazil.
    Johansson, Adam Johannes
    Pettersson, Lars G. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Properties of interfaces between copper and copper sulphide/oxide films2021Inngår i: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 183, artikkel-id 109313Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We compare different means of predicting and rationalizing properties of corrosion films aiming at gaining deeper understanding of the behaviour of copper in aqueous and sulphide-containing environments. Purely geometrical tools ranging from mean bulk information to anisotropic and facet-specific approaches are discussed, and their performances compared against DFT-based stability and property evaluations of a range of interfaces arising from combining low-index crystallographic planes of the compounds Cu, Cu2O, and Cu2S. We demonstrate the necessity to consider facet-specific interactions to understand nanolevel differences between Cu2S and Cu2O film behaviour, and that thin films cannot be directly described by bulk properties.

  • 132. Han, Lu
    et al.
    Miyasaka, Keiichi
    Terasaki, Osamu
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Graduate School of EEWS, WCU Energy Science & Engineering, Republic of Korea.
    Electron Crystallography2014Inngår i: Structure from Diffraction Methods / [ed] Duncan W. Bruce, Dermot O'Hare, Richard I. Walton, Chichester: John Wiley & Sons, 2014, s. 201-258Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    A transmission electron microscope (TEM) can provide an electron diffraction pattern on the back focal plane of the objective lens and can supply real-space information through images on the image plane. X-ray crystallography, using X-ray diffraction (XRD) with either a powder or a single-crystal diffractometer, is the most precise and most popular method of structural analysis. However, structure determination by powder XRD has its limitations. Due to this, electron crystallography (EC), which is the focus of this chapter,  is the only possible technique by which to solve/characterise the crystal structure. The chapter discusses the relationship between crystal structure and TEM images. It describes in detail, the various materials including 1D atomistic crystal, solved by EC methods. The chapter also discusses other TEM techniques such as high-angle annular dark-field imaging (HAADF) and electron tomography.

  • 133.
    Hao, Wenming
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Taiyuan University of Technology, China.
    Liu, Yongsheng
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Neagu, Alexandra
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Bacsik, Zoltan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Tai, Cheuk-Wai
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Hedin, Niklas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Core-Shell and Hollow Particles of Carbon and SiC Prepared from Hydrochar2019Inngår i: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, nr 11, artikkel-id 1835Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The applications of silicon carbide (SiC) include lightweight materials with thermal shock resistance. In this study, core-shell C-SiC particles were synthesized by compacting and rapidly heating a hydrochar from glucose by using strong pulsed currents and infiltration of silicon vapor. Hollow particles of SiC formed on removing the carbon template. In contrast to related studies, we detected not only the pure 3C polytype (-SiC) but also significant amounts of the 2H or the 6H polytypes (-SiC) in the SiC.

  • 134. Harada, Y.
    et al.
    Miyawaki, J.
    Niwa, H.
    Yamazoe, K.
    Pettersson, Lars G. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Nilsson, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Probing the OH Stretch in Different Local Environments in Liquid Water2017Inngår i: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 8, nr 22, s. 5487-5491Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We use resonant inelastic X-ray scattering (RIXS) to resolve vibrational losses corresponding to the OH stretch where the X-ray absorption process allows us to selectively probe different structural subensembles in liquid water. The results point to a unified interpretation of X-ray and vibrational spectroscopic data in line with a picture of two classes of structural environments in the liquid at ambient conditions with predominantly close-packed high-density liquid (HDL) and occasional local fluctuations into strongly tetrahedral low-density liquid (LDL).

  • 135. He, Jianqiao
    et al.
    Wang, Yan
    Yuan, Jiayin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Liu, Cheng
    Pan, Chunyue
    Weng, Zhihuan
    Tang, Xiang
    Liu, Younian
    Yu, Guipeng
    Ferrocene-integrated conjugated microporous polymer nanosheets: Active and regenerative catalysts for photomediated controlled radical polymerization2020Inngår i: Applied materials today, ISSN 2352-9407, Vol. 18, artikkel-id 100507Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The challenge of light-driven controlled radical polymerization through non-noble metal catalyst remains the most significant issue. Ferrocene-bearing microporous aromatic polymer nanosheets (termed FeMAP-11) that feature high chemical stability were reported here to synergistically combine the advantageous properties of the redox-active ferrocene units and the conjugated microporous polymers (CMPs), and to be able to serve as photocatalyst for activators regenerated by electron transfer atom transfer radical polymerization (AGET-ATRP). It succeeded in initiating polymerizations of 3 common vinyl monomers, i.e. methyl methacrylate (MMA), methacrylate (MA) and styrene (St), and produced polymers with controlled molecular weight and relatively low molecular weight dispersity ((1) over tilde .3). Benefiting from steric hindrance through ketone-amine chemistry, the microporous catalyst with tolerance to acidic and basic media was found stable under the AGET-ATRP conditions. It showed negligible metal leaching and good recyclability for at least 10 cycles without sacrifice of its catalytic performance. Our tests proved that FeMAP-11 exceeded the state-of-the-art ATRP photocatalysts such as UiO-66-NH2, titanium MOF-901 and the commercial P-25 Titania, demonstrating promising potential in catalysis in view of green chemistry.

  • 136. He, Qinglong
    et al.
    Jiang, Jie
    Yang, Xianfeng
    Zhang, Li
    Zhou, Zhe
    Zhong, Yuan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Additive manufacturing of dense zirconia ceramics by fused deposition modeling via screw extrusion2021Inngår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 41, nr 1, s. 1033-1040Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A fused deposition modeling(FDM)system via screw extrusion suitable for feeding granular feedstocks with high solid loading was developed. Key parameters included aspect ratio of the screw, the compression ratio and pitch etc. In order to get constant extruded mass flow and wire diameter a processing window was determined by optimizing the barrel temperature, the nozzle diameter and the screwing speed. Microstructural characterization coupled with flexural strength measurement revealed that a higher printing temperature was beneficial to the inter layer bonding. The sintered zirconia ceramic samples with 99% of theoretical density of the 3 mol% yttria stabilized tetragonal zirconia polycrystal (3Y-TZP) and flexural strength of 890 +/- 60 MPa was obtained. A set of zirconia ceramic parts with complex geometries and controllable dimensional accuracy was also successfully prepared for demonstrating the potential of the technique.

  • 137. Hedberg, Yolanda S.
    et al.
    Qian, Bin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Virtanen, Sannakaisa
    Odnevall Wallinder, Inger
    In-vitro biocompatibility of CoCrMo dental alloys fabricated by selective laser melting2014Inngår i: Dental Materials, ISSN 0109-5641, E-ISSN 1879-0097, Vol. 30, nr 5, s. 525-534Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Objectives: Selective laser melting (SLM) is increasingly used for the fabrication of customized dental components made of metal alloys such as CoCrMo. The main aim of the present study is to elucidate the influence of the non-equilibrium microstructure obtained by SLM on corrosion susceptibility and extent of metal release (measure of biocompatibility).Methods: A multi-analytical approach has been employed by combining microscopic and bulk compositional tools with electrochemical techniques and chemical analyses of metals in biologically relevant fluids for three differently SLM fabricated CoCrMo alloys and one cast CoCrMo alloy used for comparison.Results: Rapid cooling and strong temperature gradients during laser melting resulted in the formation of a fine cellular structure with cell boundaries enriched in Mo (Co depleted), and suppression of carbide precipitation and formation of a martensitic ε (hcp) phase at the surface. These features were shown to improve the corrosion and metal release susceptibility of the SLM alloys compared with the cast alloy. Unique textures formed in the pattern of the melting pools of the three different laser melted CoCrMo alloys predominantly explain observed small, though significant, differences. The susceptibility for corrosion and metal release increased with an increased number (area) of laser melt pool boundaries.Significance: This study shows that integrative and interdisciplinary studies of microstructural characteristics, corrosion, and metal release are essential to combine and consider during the design and fabrication of CoCrMo dental components of optimal biocompatibility. The reason is that metal release from CoCrMo alloys is dependent on the fabrication procedure.

  • 138. Heikkila, I.
    et al.
    Karlsson, O.
    Lindell, D.
    Angre, A.
    Zhong, Yuan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Olsén, Jon
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Comparison Between Microstructures, Deformation Mechanisms and Micromechanical Properties of 316L Stainless Steel Consolidated by Laser Melting2018Inngår i: La Metallurgia Italiana, ISSN 0026-0843, nr 3, s. 5-11Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A powder bed fusion laser technique (PBF-LS) was used to fabricate 316L stainless steel specimens for characterization of microstructures and micromechanical properties under uniaxial loading in-situ in a scanning electron microscope (SEM). Correlations between the microstructure, deformation mechanisms and mechanical properties were investigated. The results show that the morphology of the microstructure is very different when the sample building orientation was altered. In tensile test specimens that were machined from horizontally oriented rectangular beams, smaller grains and a more deformed microstructure were observed. Under uniaxial loading the yield strength and initial work hardening rate was highest in the horizontally built specimens. The uniform and total elongation was better for tensile test samples that were machined from vertically built rectangular specimens. Slip and twinning were the dominant deformation mechanisms with correlation to the observed texture. The observed anisotropic mechanical behavior can be explained by the differences in the distribution of deformed and sub-structured microstructures along the strain path.

  • 139. Hejral, U.
    et al.
    Plessow, P. N.
    Franz, D.
    Shipilin, Mikhail
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Gutowski, O.
    Rutt, U.
    Noei, H.
    Vonk, V.
    Stierle, A.
    Composition-Dependent Alloy Nanoparticle Shape Changes under Reaction Conditions: Kinetic and Thermodynamic Effects2024Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 128, nr 10, s. 4330-4342Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Particle sintering and reshaping constitute the main cause for catalyst deactivation. An atomic-scale understanding of the correlation among the catalyst structure, its support, and the gas phase under realistic reaction conditions is required for its suppression. In this study, we combined high-energy grazing incidence X-ray diffraction, in situ mass spectrometry, ex situ scanning electron microscopy, and density functional theory calculations to unravel the driving force behind the composition-dependent particle shape changes and sintering processes of alpha-Al2O3(0001)-supported Pt-Pd alloy nanoparticles under realistic reaction conditions for CO oxidation. We find that pure Pt and Pt-rich particles, initially kinetically trapped in metastable flat particle shapes, undergo a strong reaction-induced height increase to adopt a more stable, theoretically predicted compact equilibrium shape. Contrarily, Pd-rich particles prove to be more resistant against shape changes, since they exhibit already a shape close to equilibrium. We thus conclude that the observed initial deviations in particle shape from the theoretical predictions are due to kinetic limitations during growth. Our data provide information on the segregation state of the alloy particles, indicating a Pt core and Pd shell structure under strongly reducing conditions and the alloying of Pt and Pd under the reaction conditions for CO oxidation close to stoichiometry.

  • 140. Herrera, Chloe
    et al.
    Cerbin, Jonah
    Jayakody, Amani
    Dunnett, Kirsty
    Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita).
    Balatsky, Alexander V.
    Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita). University of Connecticut, USA.
    Sochnikov, Ilya
    Strain-engineered interaction of quantum polar and superconducting phases2019Inngår i: Physical Review Materials, E-ISSN 2475-9953, Vol. 3, nr 12, artikkel-id 124801Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The pairing mechanism of unconventional superconductivity in strontium titanate is hotly debated. Here, using a multisensor experimental apparatus with a mechanical strain cell, an optical microscope, and with transport and magnetic probes all contained in a closed-cycle dilution refrigerator, we determined that the superconducting transition temperature of strontium titanate increases dramatically even for very small strains induced by application of uniaxial tension. These results imply that superconductivity is controlled by very small atomic shifts; the only strain-sensitive pairing channel candidate is the one linked to quantum ferroelectric (polar) instability. This investigation, therefore, uncovers additional constraints on the debated theories of superconductivity in this low carrier concentration material near the ferroelectric quantum phase transition.

  • 141. Herrera, Martha A.
    et al.
    Mathew, Aji P.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Luleå University of Technology, Sweden.
    Oksman, Kristiina
    Barrier and mechanical properties of plasticized and cross-linked nanocellulose coatings for paper packaging applications2017Inngår i: Cellulose, ISSN 0969-0239, E-ISSN 1572-882X, Vol. 24, nr 9, s. 3969-3980Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Barrier, mechanical and thermal properties of porous paper substrates dip-coated with nanocellulose (NC) were studied. Sorbitol plasticizer was used to improve the toughness, and citric acid cross-linker to improve the moisture stability of the coatings. In general, the addition of sorbitol increased the barrier properties, maximum strength and toughness as well as the thermal stability of the samples when compared to the non-modified NC coatings. The barrier properties significantly improved, especially for plasticized NC coating's, where the oxygen permeability value was as low as 0.7 mL mu m day(-1) m(-2) kPa(-1) at 49% RH and the water vapor permeability was reduced by 60%. Furthermore, we found that the cross-linked plasticized NC coating had a smoother surface (50% lower roughness) compared to non-modified ones. This study shows that the environmentally friendly additives sorbitol and citric acid had positive effects on NC coating properties, increasing its potential use in paper-based packaging applications.

  • 142. Hertzberg, Benjamin J.
    et al.
    Huang, An
    Hsieh, Andrew
    Chamoun, Mylad
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Davies, Greg
    Seo, Joon Kyo
    Zhong, Zhong
    Croft, Mark
    Erdonmez, Can
    Meng, Ying Shirley
    Steingart, Dan
    Effect of Multiple Cation Electrolyte Mixtures on Rechargeable Zn-MnO2 Alkaline Battery2016Inngår i: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 28, nr 13, s. 4536-4545Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A Bi2O3 in beta-MnO2 composite cathode material has been synthesized using a simple hydrothermal method and cycled in a mixed KOH-LiOH electrolyte with a range of concentrations. We show that, at a KOH:LiOH molar ratio of 1:3, both proton insertion and lithium insertion occur, allowing access to a higher fraction of the theoretical capacity of the MnO2 while preventing the formation of ZnMn2O4. This enables a capacity of 360 mAh/g for over 60 cycles, with cycling limited more by anode properties than traditional cathodic failure mechanisms. The structural changes occurring during cycling are characterized using electron microscopy and in situ synchrotron energy-dispersive X-ray diffraction (EDXRD) techniques. This mixed electrolyte shows exceptional cyclability and capacity and can be used as a drop-in replacement for current alkaline batteries, potentially drastically improving their cycle life and creating a wide range of new applications for this energy storage technology.

  • 143. Heydarian, Abtin
    et al.
    Sajjadi, Seyed Abdolkarim
    Johnsson, Mats
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    A proposed model for spark plasma sintering of SiC-Si nanocomposite with different SiC particle sizes2020Inngår i: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 54, nr 19, s. 2599-2609Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, the effect of SiC particle size on the sintering behavior of SiC-Si nano composites fabricated by spark plasma sintering (SPS) technique was investigated and a model was proposed, accordingly. To this purpose, SiC powders with three different particle sizes of 25 mu m, 80 nm and 45 nm were chosen. It was expected that hardness of the composites increase with decreasing the SiC particle size; however, the outcomes were interesting and unpredictable. The composite with 80 nm SiC particles indicated the highest hardness. Hardness of the specimen with 25 mu m SiC was low because of the large particle size of its reinforcement. While 80 and 45 nm SiC particles are considered as nano particles, the composite with 45 nm SiC particles showed lower hardness due to the growth of SiC powders during sintering according to a proposed model. Two reasons for the growth of 45 nm SiC particles were defined: (i) the fineness of the SiC particles prevented the Si particles to act as a binder between them thus, they agglomerated; (ii) SiC powders were oxidized during mixing procedure and a layer of SiO2 was formed on their surfaces. During sintering procedure, the reaction between SiC and SiO2 was happened and as a result SiO was formed. It caused vapor transportation during sintering leading to necking between particles and in turn, grain growth.

  • 144. Heydarian, Abtin
    et al.
    Sajjadi, Seyed Abdolkarim
    Kern, Frank
    Johnsson, Mats
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Characteristics evaluation of SiC/Si nanocomposites produced by spark plasma sintering2019Inngår i: Materials Science and Technology, ISSN 0267-0836, E-ISSN 1743-2847, Vol. 35, nr 10, s. 1204-1211Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    SiC-Si composites are widely used either as a bulk material or as a matrix for fibre reinforced ceramics. In the current research, nanocomposites of SiC-Si with different volume fractions of Si were sintered by spark plasma sintering (SPS) for the first time. The effect of Si content and different sintering parameters on relative density, microstructure, hardness and fracture toughness of the sintered materials have been investigated. The relative density increased from about 83 to 99% by increasing the sintering temperature to 1700 degrees C, sintering time to 10 min, and pressure to 70 MPa for composites containing >20 vol.-% Si. The results revealed that the full dense SiC-20 vol.-%Si composite can be obtained by SPS at 1700 degrees C, 10 min and 70 MPa. Moreover, in this condition, the hardness and toughness of the composites reached the optimum values.

  • 145. Holt, Ann Julie U.
    et al.
    Pakdel, Sahar
    Rodríguez-Fernández, Jonathan
    Zhang, Yu
    Curcio, Davide
    Sun, Zhaozong
    Lacovig, Paolo
    Yao, Yong-Xin
    Lauritsen, Jeppe V.
    Lizzit, Silvano
    Lanatà, Nicola
    Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita).
    Hofmann, Philip
    Bianchi, Marco
    Sanders, Charlotte E.
    Electronic properties of single-layer CoO2/Au(111)2021Inngår i: Current Opinion in Chemical Engineering, E-ISSN 2211-3398, Vol. 8, nr 3, artikkel-id 035050Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report direct measurements via angle-resolved photoemission spectroscopy (ARPES) of the electronic dispersion of single-layer (SL) CoO2. The Fermi contour consists of a large hole pocket centered at the point. To interpret the ARPES results, we use density functional theory (DFT) in combination with the multi-orbital Gutzwiller Approximation (DFT+GA), basing our calculations on crystalline structure parameters derived from x-ray photoelectron diffraction and low-energy electron diffraction. Our calculations are in good agreement with the measured dispersion. We conclude that the material is a moderately correlated metal. We also discuss substrate effects, and the influence of hydroxylation on the CoO2 SL electronic structure.

  • 146. Hooshmand, Saleh
    et al.
    Aitomäki, Yvonne
    Berglund, Linn
    Mathew, Aji P.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Luleå University of Technology, Sweden.
    Oksman, Kristiina
    Enhanced alignment and mechanical properties through the use of hydroxyethyl cellulose in solvent-free native cellulose spun filaments2017Inngår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 150, s. 79-86Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, the addition of hydroxyethyl cellulose (HEC) in cellulose nanofiber filaments is shown to improve the solvent-free processing and mechanical properties of these biobased fibers as well as their compatibility with epoxy. An aqueous dope of cellulose nanofiber (CNF) with HEC was spun and the resulting filaments cold-drawn. The HEC increased the wet strength of the dope allowing stable spinning of low concentrations of CNF. These lower concentrations promote nanofiber alignment which is further improved by cold-drawing. Alignment improves the modulus and strength and an increase of over 70% compared to the as-spun CNF only filaments was achieved. HEC also decreases hydrophilicity thus increasing slightly the interfacial shear strength of the filaments with epoxy resin. The result is continuous biobased fibers with improved epoxy compatibility that can be prepared in an upscalable and environmentally friendly way. Further optimization is expected to increase draw ratio and consequently mechanical properties.

  • 147. Hu, Jianfeng
    et al.
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Grain growth competition during sintering of SrTiO3 nanocrystals: Ordered coalescence of nanocrystals versus conventional mechanism2021Inngår i: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 194, artikkel-id 113703Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Grain growth plays a crucial role in developing the microstructures of polycrystalline materials during heating treatment. In this work, SrTiO3 ceramics sintered at different heating rates (10 degrees C/min and 100 degrees C/min) display the distinctly different grain growth behaviors and microstructures between them. The onset temperature of rapid grain growth and mechanical-performance-related fracture mode are apparently different between these two sets of samples. Two grain growth mechanisms are demonstrated to dominate separately the sintering of SrTiO3 nanocrystals at different heating rates, i.e. conventional mechanism of atom-by-atom additions for grain growth at 10 degrees C/min and ordered coalescence of nanocrystals for grain growth at 100 degrees C/min. It is demonstrated that the switch of growth mechanisms is determined by the competition between the activation of grain motions and the formation of steady neck among grains.

  • 148.
    Hu, Jianfeng
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Intragranular heterojunctions formed by ordered coalescence of strontium and barium titanate nanocrystals2015Inngår i: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 107, s. 14-17Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Crystal growth by nanocrystal-assembly plays an important role in the synthesis and preparation of nanostructural materials. In most cases, this crystal-growth mechanism is reported to occur in unary nanocrystal systems and in solution environment. Here, we report a new observation of grain growth by ordered coalescence of nanocrystals occurring in SrTiO3-BaTiO3 binary system during solid-state sintering, which also results in unique oxide heterostructures inside coarsened grains in bulk polycrystalline materials.

  • 149.
    Hu, Jianfeng
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Ordered coalescence of nano crystallites contributing to the rapid anisotropic grain growth in silicon nitride ceramics2013Inngår i: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 69, nr 3, s. 270-273Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Microstructural characterization is performed on two dense Si3N4 ceramic samples consolidated by spark plasma sintering (SPS): one fabricated using alpha-Si3N4 and the other using beta-Si3N4 as the starting powder. A novel mechanism is revealed where ordered coalescence of nano beta-crystallites accelerate the rapid beta-Si3N4 anisotropic grain growth. The rapid alpha- to beta-Si3N4 phase transformation via a high supersaturation of dissolved Si3N4 in the melt favors this mechanism. The high heating rate by SPS is essential for achieving such supersaturation.

  • 150. Hu, Jianfeng
    et al.
    Wang, Xianhao
    Zhang, Junzhan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Xi’an University of Architecture and Technology, China.
    Luo, Jun
    Zhang, Zhijun
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    A general mechanism of grain growth -I. Theory2021Inngår i: Journal of Materiomics, ISSN 2352-8478, E-ISSN 2352-8486, Vol. 7, nr 5, s. 1007-1013Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The behaviors of grain growth dominate the formation of the microstructure inside polycrystalline materials and thus strongly influence their practical performances. However, grain growth behaviors still remain ambiguous and thus lack a mathematical formula to describe the general evolution despite decades of efforts. Here, we propose a new migration model of grain boundary (GB) and further derive a mathematical expression to depict the general evolution of grain growth in the cellular structures. The expression incorporates the variables influencing growth rate (e.g. GB features, grain size and local grain size distribution) and thus reveals how the normal, abnormal and stagnant behaviors of grain growth occur in polycrystalline systems. In addition, our model correlates quantitatively GB roughening transition with grain growth behavior. The general growth theory may provide new insights into the GB thermodynamics and kinetics during the cellular structure evolution.

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