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  • 1. Arzbacher, S.
    et al.
    Amann, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Weidenfeller, B.
    Loerting, T.
    Ostermann, A.
    Petrasch, J.
    Tomography based numerical simulation of the demagnetizing field in soft magnetic composites2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, no 16, article id 163905Article in journal (Refereed)
    Abstract [en]

    The magneto-static behaviour of soft magnetic composites (SMCs) is investigated using tomography based direct numerical simulation. The microgeometry crucially affects the magnetic properties of the composite since a geometry dependent demagnetizing field is established inside the composite, which lowers the magnetic permeability. We determine the magnetic field information inside the SMC using direct numerical simulation of the magnetic field based on high resolution micro-computed tomography data of the SMC's microstructure as well as artificially generated data made of statistically homogeneous systems of identical fully penetrable spheres and prolate spheroids. Quasi-static electromagnetic behaviour and linear material response are assumed. The 3D magnetostatic Maxwell equations are solved using Whitney finite elements. Simulations show that clustering and percolation behaviour determine the demagnetizing factor of SMCs rather than the particle shape. The demagnetizing factor correlates with the slope of a 2-point probability function at its origin, which is related to the specific surface area of the SMC. Comparison with experimental results indicates that the relatively low permeability of SMCs cannot be explained by demagnetizing effects alone and suggests that the permeability of SMC particles has to be orders of magnitude smaller than the bulk permeability of the particle material.

  • 2. Björnetun Haugen, Astri
    et al.
    Morozov, Maxim I.
    Johnsson, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Grande, Tor
    Einarsrud, Mari-Ann
    Effect of crystallographic orientation in textured Ba0.92Ca0.08TiO3 piezoelectric ceramics2014In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 116, no 13, p. 134102-Article in journal (Refereed)
    Abstract [en]

    Strongly textured lead-free Ba0.92Ca0.08TiO3 piezoelectric ceramics were fabricated by tape casting and templated grain growth. Dense ceramics with both favorable < 100 > and unfavorable < 111 > texture were successfully prepared. Enhanced piezoelectric performance was demonstrated for ceramics with < 100 > texture, in line with the predictions based on reported piezoelectric coefficients of tetragonal BaTiO3. Due to the expanded tetragonal range through Ca-substitution, < 100 > texture is favorable over a wide temperature range. The < 100 > texture also results in the enhanced piezoelectric performance being temperature-independent. In addition to engineering of stable, high-performance lead-free piezoelectric ceramics, this study has demonstrated that consideration of the extender/rotator nature of piezoelectric properties is imperative for improving the piezoelectric response through texturing.

  • 3. Buixaderas, E.
    et al.
    Bovtun, V.
    Kempa, M.
    Savinov, M.
    Nuzhnyy, D.
    Kadlec, F.
    Vanek, P.
    Petzelt, J.
    Eriksson, M.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Broadband dielectric response and grain-size effect in K0.5Na0.5NbO3 ceramics2010In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 107, no 1, p. 14111-Article in journal (Refereed)
    Abstract [en]

    Dielectric spectra of two K0.5Na0.5NbO3 ceramics with different grain sizes (10 and 0.5 mu m) were measured from 10(2) to 10(14) Hz in a broad temperature range. The sequence of first-order phase transitions (cubic-tetragonal-orthorhombic-rhombohedral) was detected by differential scanning calorimetry, dielectric spectroscopy, and time-domain terahertz spectroscopy. The grain size affects all the phase transitions, which are more smeared in the small-grain sample. In the large-grain ceramics, two well-separated near-Debye relaxations are seen in the tetragonal phase, which suddenly merge on cooling across the tetragonal-orthorhombic transition, and on further cooling the lower-frequency relaxation strongly broadens. On reducing the grain size, the higher-frequency relaxation shifts from similar to 1 to similar to 20 GHz and the lower-frequency one strongly broadens. Without quantitative understanding, these effects could be assigned to domain-wall dynamics and its temperature and grain-size dependences. Similar to pure KNbO3, an overlapped central-mode-soft-mode type excitation was detected in the terahertz range related to the effective hopping and oscillations of the off-centered Nb ions in a multiwell potential.

  • 4. Cederkrantz, D.
    et al.
    Farahi, N.
    Borup, K. A.
    Iversen, B. B.
    Nygren, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Palmqvist, A. E. C.
    Enhanced thermoelectric properties of Mg2Si by addition of TiO2 nanoparticles2012In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 111, no 2, article id 023701Article in journal (Refereed)
    Abstract [en]

    The effects on the thermoelectric properties of Mg2Si when adding TiO2 nanoparticles have been evaluated experimentally. A batch of Mg2Si was prepared through direct solid state reaction and divided into portions which were mechanically mixed with different amounts of TiO2 nanoparticles ranging from 0.5 to 3 vol% and subsequently sintered to disks. All materials showed n-type conduction and the absolute value of the Seebeck coefficient was reduced with increasing amount of TiO2 added, while the electrical resistivity was greatly reduced. The thermal conductivity was surprisingly little affected by the addition of the nanoparticles. An optimum value of the thermoelectric figure-of-merit ZT = TS2 sigma/k was found for the addition of 1 vol% TiO2, showing almost three times higher ZT value than that of the pure Mg2Si. Larger TiO2 additions resulted in lower ZT values and with 3 vol% added TiO2 the ZT was comparable to the pure Mg2Si. The sintering process resulted in reduction or chemical reaction of all TiO2 to TiSi2 and possibly elemental titanium as well as reduced TiOx. The increased electrical conductivity and the decreased Seebeck coefficient were found due to an increased charge carrier concentration, likely caused by the included compounds or titanium-doping of the Mg2Si matrix. The low observed effect on the thermal conductivity of the composites may be explained by the relatively higher thermal conductivity of the included compounds, counter-balancing the expected increased grain boundary scattering. Alternatively, the introduction of compounds does not significantly increase the concentration of scattering grain boundaries.

  • 5. Cederkrantz, D.
    et al.
    Nygren, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Palmqvist, A. E. C.
    Thermoelectric properties of partly Sb- and Zn-substituted Ba(8)Ga(16)Ge(30) clathrates2010In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, no 11, p. 113711-Article in journal (Refereed)
    Abstract [en]

    The effects on the thermoelectric properties of n-Ba(8)Ga(16)Ge(30) when substituting small amounts of the Ga or Ge with Sb or Zn have been investigated. A number of syntheses were prepared in quaternary systems of Ba(8)Ga(16)Ge(30) substituted with either Sb or Zn but only three samples were found to yield single phase products with nominal compositions of Ba(8)Ga(15)Sb(1)Ge(30), Ba(8)Ga(15)Zn(1)Ge(30) and Ba(8)Ga(16)Ge(28)Zn(2), respectively. When Ge was substituted for Zn the resulting sample remained n-type and an increase in thermopower and a decrease in thermal conductivity were achieved. These positive effects were accompanied with an increased electrical resistivity and thus the ZT was only somewhat improved up to about 400 degrees C. When substituting Ga with either Sb or Zn samples remained n-type but showed decreased thermopower and increased electrical resistivity and thermal conductivity. It is thus concluded that substitution of Ga with Zn or Sb is detrimental for the thermoelectric properties of Ba(8)Ga(16)Ge(30), whereas substitution of Ge with Zn appears a potent method for improving its performance.

  • 6. Crook, Charles B.
    et al.
    Houchins, Gregory
    Zhu, Jian-Xin
    Balatsky, Alexander V.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Los Alamos National Laboratory, USA.
    Constantin, Costel
    Haraldsen, Jason T.
    Spatial dependence of the super-exchange interactions for transition-metal trimers in graphene2018In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 123, no 1, article id 013903Article in journal (Refereed)
    Abstract [en]

    This study examines the magnetic interactions between spatially variable manganese and chromium trimers substituted into a graphene superlattice. Using density functional theory, we calculate the electronic band structure and magnetic populations for the determination of the electronic and magnetic properties of the system. To explore the super-exchange coupling between the transition-metal atoms, we establish the magnetic ground states through a comparison of multiple magnetic and spatial configurations. Through an analysis of the electronic and magnetic properties, we conclude that the presence of transition-metal atoms can induce a distinct magnetic moment in the surrounding carbon atoms as well as produce a Ruderman-Kittel-Kasuya-Yosidalike super-exchange coupling. It is hoped that these simulations can lead to the realization of spintronic applications in graphene through electronic control of the magnetic clusters.

  • 7.
    Elihn, Karine
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Landstroem, L.
    Alm, O.
    Boman, M.
    Heszler, P.
    Size and structure of nanoparticles formed via ultraviolet photolysis of ferrocene2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 3, p. 34311-Article in journal (Refereed)
    Abstract [en]

    Iron nanoparticles enclosed in carbon shells were formed by laser-assisted chemical vapor decomposition of ferrocene (Fe(C5H5)(2)) vapor in Ar gas atmosphere. The particle size dependence on the total ambient gas pressure and on laser fluence of the pulsed ArF excimer laser was examined and, e.g., an effective size decrease of the iron core was observed at elevated laser fluences. Characterizations of the iron and carbon microstructures were performed by x-ray diffraction and transmission electron microscopy, while relative iron deposition rates were measured by x-ray fluorescence spectroscopy. Both alpha-Fe and gamma-Fe phases were found for the single crystalline iron cores, surrounded by graphitic (inner) and amorphous (outer) carbon layers. The temperature rise of the laser-excited particles was also determined by optical spectroscopy of the emitted thermal radiation, which allowed an estimation of the iron loss of the nanoparticles due to evaporation. The estimated and measured iron losses are in good agreement. 

  • 8.
    Golod, Taras
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Rydh, Andreas
    Stockholm University, Faculty of Science, Department of Physics.
    Krasnov, Vladimir M.
    Stockholm University, Faculty of Science, Department of Physics.
    Anomalous Hall effect in NiPt thin films2011In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 110, no 3, p. 033909-Article in journal (Refereed)
    Abstract [en]

    We study Hall effect in sputtered NixPt1-x thin films with different Ni concentrations. Temperature, magnetic field andangular dependencies are analyzed and the phase diagram of NiPt thin films is obtained. It is found that films with sub-critical Ni concentration exhibit cluster-glass behavior at low temperatures with a perpendicular magnetic anisotropy below the freezing temperature. Films with super-critical Ni concentration are ferromagnetic with parallel anisotropy. At the critical concentration the state of the film is strongly frustrated. Such films demonstrate canted magnetization with the easy axis rotating as a function of temperature. The magnetism appears via consecutive paramagnetic - cluster glass - ferromagnetic transitions, rather than a single second-order phase transition. But most remarkably, the extraordinary Hall effect changes sign at the critical concentration. We suggest that this is associated with a reconstruction of the electronic structure of the alloy at the normal metal - ferromagnet quantum phase transition.

  • 9. Hagman, H.
    et al.
    Sjolund, P.
    Petra, S. J. H.
    Nylen, M.
    Kastberg, A.
    Ellmann, H.
    Stockholm University, Faculty of Science, Department of Physics.
    Jersblad, J.
    Stockholm University, Faculty of Science, Department of Physics.
    Assessment of a time-of-flight detection technique for measuring small velocities of cold atoms2009In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 105, no 8, p. 83109-Article in journal (Refereed)
    Abstract [en]

    A low noise time-of-flight detection system for laser cooled atoms has been constructed and incrementally optimized. Here, a thorough description of the construction is presented along with an analysis of the capabilities of the system. The quality of the detection (the resolution, the reproducibility, the sensitivity, etc.) is crucial for, e.g., the ability to see details in the velocity distribution profile, which is of interest for fundamental studies of statistical physics and of the laser cooling processes, and for detection of small initial velocities of an atomic cloud, important, e.g., when studying small drifts induced by Brownian motors and ratchets. We estimate the signal-to-noise ratio of our signal to be better than 1000:1 for a typical single shot, and we discuss the effect of the initial atomic cloud size, the probe size, and the effects of the wave packet spread during the fall time on the measured quantities. We show that the shape of the velocity distribution is well conserved during the mapping done in the detection, i.e., in the convolution with the probe beam, and that velocities as small as a few percent of the single photon recoil velocity can be resolved.

  • 10. Heijl, R.
    et al.
    Cederkrantz, D.
    Nygren, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Palmqvist, A. E. C.
    Thermoelectric properties of Ba8Ga16Ge30 with TiO2 nanoinclusions2012In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 112, no 4, p. 044313-Article in journal (Refereed)
    Abstract [en]

    The effects on thermal and electrical properties of adding small amounts of TiO2 nanoinclusions to bulk Ba8Ga16Ge30 clathrate have been investigated. The thermal properties were analysed using the transient plane source technique and the analysis showed a significant decrease in thermal conductivity as the volume fraction of TiO2 increased from 0 vol. % to 1.2 vol. %. The introduction of TiO2 nanoparticles caused a shift in the peak value of the Seebeck coefficient towards lower temperatures. The maximum value of the Seebeck coefficient was, however, only little affected. The introduction of TiO2 nanoparticles into the bulk Ba8Ga16Ge30 resulted in an increased electrical resistivity of the sample, thus simultaneously reducing the charge carrier contribution to the thermal conductivity, partly explaining the decrease in total thermal conductivity. Due to the large increase in resistivity of the samples, ZT was only somewhat improved for the material with 0.4 vol. % TiO2 while the ZT values of the other materials were lower than for the reference Ba8Ga16Ge30 material without TiO2 nanoparticles. The combined results are consistent with a scenario where the nanoparticle introduction causes a light doping of the semiconductor matrix and an increased concentration of phonon scattering centres.

  • 11. Karelina, L. N.
    et al.
    Hovhannisyan, Razmik A.
    Stockholm University, Faculty of Science, Department of Physics. Moscow Institute of Physics and Technology, Russia.
    Golovchanskiy, I. A.
    Chichkov, V.
    Ben Hamida, A.
    Stolyarov, V. S.
    Uspenskaya, L. S.
    Erkenov, Sh A.
    Bolginov, V. V.
    Ryazanov, V. V.
    Scalable memory elements based on rectangular SIsFS junctions2021In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 130, no 17, article id 173901Article in journal (Refereed)
    Abstract [en]

    We explore the concept of the Josephson magnetic memory element based on a multilayer two-barrier SIsFS Josephson junction storing the digital state by means of the orientation of magnetization in the F-layer. A diluted PdFe alloy with 1% magnetic atoms is used as a ferromagnet (F), and a tunnel A1Ox layer (I) ensures a high voltage in the resistive state. We have studied two junctions of a rectangular shape in which two digital states are defined by the orientation of the residual F-layer magnetization set along or across the junction in the plane of the ferromagnetic barrier. Implementations of both binary and ternary logic elements are demonstrated. A scalability of rectangular memory elements is analyzed using micro-magnetic modeling.

  • 12. Krycka, K. L.
    et al.
    Borchers, J. A.
    Laver, M.
    Salazar Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Lopez-Ortega, A.
    Estrader, M.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Surinach, S.
    Baro, M. D.
    Sort, J.
    Nogues, J.
    Correlating material-specific layers and magnetic distributions within onion-like Fe3O4/MnO/gamma-Mn2O3 core/shell nanoparticles2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 17, p. 17B531-Article in journal (Refereed)
    Abstract [en]

    The magnetic responses of two nanoparticle systems comprised of Fe3O4/gamma-Mn2O3 (soft ferrimagnetic, FM/hard FM) and Fe3O4/MnO/gamma-Mn2O3 (soft FM/antiferromagnetic, AFM/hard FM) are compared, where the MnO serves to physically decouple the FM layers. Variation in the temperature and applied field allows for Small Angle Neutron Scattering (SANS) measurements of the magnetic moments both parallel and perpendicular to an applied field. Data for the bilayer particle indicate that the graded ferrimagnetic layers are coupled and respond to the field as a single unit. For the trilayer nanoparticles, magnetometry suggests a Curie temperature (T-C) approximate to 40 K for the outer gamma-Mn2O3 component, yet SANS reveals an increase in the magnetization associated with outer layer that is perpendicular to the applied field above T-C during magnetic reversal. This result suggests that the gamma-Mn2O3 magnetically reorients relative to the applied field as the temperature is increased above 40 K.

  • 13. Li, Ming
    et al.
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Nygren, Mats
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Origin(s) of the apparent high permittivity in CaCu3Ti4O12 ceramics: Clarification on the contributions from internal barrier layer capacitor and sample-electrode contact effects2009In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 106, no 10, p. 104106/1-104106/8Article in journal (Refereed)
    Abstract [en]

    CaCu3Ti4O12 ceramics with a range of resistivities have been prepared using both conventional sintering and spark plasma sintering. For all cases, the high effective permittivity is associated primarily with an internal barrier layer capacitor mechanism. Additional polarization associated with the electrode-sample interface may appear but its visibility depends on the grain boundary resistivity (Rgb) of the ceramic. If the Rgb is large, the electrode polarization is obscured by sample-related effects; if the Rgb is small, a separate impedance associated with the electrode polarization may be seen. Discrepancies in the literature regarding the magnitude and origin of the high effective permittivity are attributed to a combination of differences in processing conditions, electrode contact material and measuring frequency range

  • 14. Litvinchuk, A. P.
    et al.
    Nylén, Johanna
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Lorenz, B.
    Guloy, A. M.
    Haeussermann, U.
    Optical and electronic properties of metal doped thermoelectric Zn4Sb32008In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 103, no 12, article id 123524Article in journal (Refereed)
    Abstract [en]

    Optical and electronic properties of metal (Pb, Bi, Sn, and In) doped Zn4Sb3 are reported in the temperature range 80-300 K, which covers the beta, alpha, and alpha(') structural phases of this thermoelectric material. Metal doping alters the subtle balance between Zn disorder and Zn deficiency present in beta-Zn4Sb3 and changes its low temperature structural behavior. Analysis of infrared reflection data shows that the formation of ordered alpha'-Zn4Sb3 is accompanied by a substantial increase in the free charge-carrier concentration. In contrast, for samples where doping suppresses the occurrence of the low temperature alpha'-phase, the free charge-carrier concentration is only weakly temperature dependent. Different degrees of structural disorder in doped beta-Zn4Sb3 and the ordering processes at low temperatures leading to alpha- and alpha'-Zn4Sb3 are also recognized in the charge-carrier dynamics. 

  • 15.
    Liu, Jing
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Inorganic Chemistry.
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Inorganic Chemistry.
    Yan, Haixue
    Reece, Michael J.
    Kan, Yanmei
    Wang, Peiling
    Dielectric, piezoelectric, and ferroelectric properties of grain-orientated Bi3.25La0.75Ti3O12 ceramics2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 102, no 10, p. 104107-Article in journal (Refereed)
    Abstract [en]

    By dynamic forging during Spark Plasma Sintering (SPS), grain-orientated ferroelectric Bi3.25La0.75Ti3O12 (BLT) ceramics were prepared. Their ferroelectric, piezoelectric, and dielectric properties are anisotropic. The textured ceramics parallel and perpendicular to the shear flow directions have similar thermal depoling behaviors. The d(33) piezoelectric coefficient of BLT ceramics gradually reduces up to 350 degrees C; it then drops rapidly. The broadness of the dielectric constant and loss peaks and the existence of d(33) above the permittivity peak, T-m, show that the BLT ceramic has relaxor-like behavior.

  • 16.
    Neagu, Alexandra
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Tai, Cheuk-Wai
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Investigation of local structural phase transitions in 95Na(0.5)Bi(0.5)TiO(3)-5BaTiO(3) piezoceramics by means of in-situ transmission electron microscopy2018In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 123, no 24, article id 244105Article in journal (Refereed)
    Abstract [en]

    The temperature-dependence of superstructure reflections, diffuse scattering intensity, and ferroelectric domain morphology for 95Na(0.5)Bi(0.5)TiO(3)-5BaTiO(3) ceramics was investigated by in-situ transmission electron microscopy. A subtle local structural phase transition was observed around 110 degrees C. This local phase transition is characterized by a transformation in the dominant octahedral-tilt system from antiphase to in-phase tilting and was correlated with the depolarization mechanism common in this type of materials. Simulations of the octahedral-tilt disorder were developed at different temperatures which enabled us to provide a comprehensive structural model that explains the temperature-dependence of superstructure reflections and electron diffuse scattering intensity. This model revealed that plate-like in-phase nanodomains tilted about three orthogonal axes coexist with an antiphase tilted matrix, even at room temperature. With increasing temperature, the concentration of in-phase nanodomains is increased till a critical volume fraction is reached. We propose that these plate-like in-phase nanodomains are an inherent characteristic of NBT-based compounds and that the local phase transition observed around 110 degrees C leads to a disruption in the long-range ferroelectric order and is responsible for the depolarization mechanism.

  • 17. Pedersen, Birgitte L.
    et al.
    Birkedal, Henrik
    Nygren, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Frederiksen, Poul Toft
    Iversen, Bo B.
    The effect of Mg doping on the thermoelectric performance of Zn4Sb32009In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 105, no 1, p. 13517-Article in journal (Refereed)
    Abstract [en]

    Cation doping studies of high performance thermoelectric (ZnSb3)-Sb-4 have so far focused on elements with larger electronegativity than Zn. Mg has a lower electronegativity than Zn, and, in the present paper, the effect of Mg doping of Zn4Sb3 on phase transition temperatures and thermal and thermoelectric properties have been studied on five samples with a doping degree ranging from 0.1 to 2 at. % Mg. The results are compared with data obtained for a pure, undoped sample. Laboratory x-ray powder diffraction shows that all samples are single phase materials as further evidenced with higher confidence by Rietveld refinement of high resolution synchrotron powder diffraction of as synthesized 1 and 2 at. % Mg doped samples. Multitemperature synchrotron powder diffraction and differential scanning calorimetry reveal a significant effect of Mg-doping on the low temperature phase transitions in one sample (0.5 at. % Mg), whereas the other samples showed only small or no effect. Physical properties have been evaluated from 2-400 K for all samples. Some physical property parameters are affected by doping but no immediate improvement of ZT was achieved. The reason for this is discussed in relation to differences in sample compaction. 

  • 18. Rajan, Akhil
    et al.
    Davidson, Ian A.
    Stockholm University, Faculty of Science, Department of Physics. Heriot Watt Univ, Sch Engn & Phys Sci, SUPA, Inst Photon & Quantum Sci, Edinburgh, Midlothian, Scotland.
    Moug, Richard T.
    Prior, Kevin A.
    Epitaxial lift-off of II-VI semiconductors from III-V substrates using a MgS release layer2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 114, no 24, p. 243510-Article in journal (Refereed)
    Abstract [en]

    Epitaxial lift-off (ELO) is a post-growth process that allows an epitaxial layer to be removed from its original substrate and transferred to a new one. ELO has previously been successfully demonstrated for III-V materials and also ZnSe based II-VI semiconductors using a MgS sacrificial layer. Following the recent successful growth of epitaxial MgS layers on GaP and InP substrates, in this paper we compare ELO of II-VI epilayers grown on GaP, GaAs, and InP substrates using MgS sacrificial layers in the range of 7-15 nm thick. Good quality lifted layers are obtained rapidly from InP and GaAs substrates. For GaP substrates, ELO is much slower and good quality lifts have only been achieved with ZnSe epilayers. Photoluminescence spectra obtained from epitaxial layers before and after ELO show changes in peak positions, which are compatible with changes of strain in the layer. The layers produced by ELO are flat and free of cracks, suggesting that this is an efficient and convenient method for the transfer of II-VI epitaxial layers to other substrates.

  • 19.
    Stingaciu, Marian
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Kremer, Reinhard K.
    Lemmens, Peter
    Johnsson, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Magnetoresistivity in CoFe(2)O(4)-BaTiO(3) composites produced by spark plasma sintering2011In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 110, no 4, p. 044903-Article in journal (Refereed)
    Abstract [en]

    Ceramic composites of (CoFe(2)O(4))(x)-(BaTiO(3))((1-x)) with x = 0.20, 0.25, and 0.30 have been synthesized by spark plasma sintering at 1000 degrees C under a uniaxial pressure of 75 MPa using commercially available nanopowders as starting materials. The composites reveal a negative magnetoresistivity effect of about -1% at room temperature. An enhancement was observed at lower temperatures, and an effect of -4.1% was found in the composite with x 0.30 at 150 K by applying an external magnetic field of 25 kOe. The temperature dependence of the resistivity indicates variable range hopping involved in charge transport.

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