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  • 1. Bell, Thomas
    et al.
    Celania, Chris R.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Smetana, Volodymyr
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mudring, Anja-Verena
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Meyer, Gerd
    Tb3Pd2, Er3Pd2 and Er6Co5-x: structural variations and bonding in rare-earth-richer binary intermetallics2018In: Acta crystallographica. Section C, Structural chemistry, ISSN 2053-2296, Vol. 74, no 9, p. 991-996Article in journal (Refereed)
    Abstract [en]

    The three binary Tb/Er-rich transition metal compounds Tb3Pd2 (triterbium dipalladium), Er3Pd2 (trierbium dipalladium) and Er6Co5-x (hexaerbium pentacobalt) crystallize in the space groups Pbam (Pearson symbol oP20), P4/mbm (tP10) and P6(3)/m (hP22), respectively. Single crystals of Tb3Pd2 and Er6Co5-x suitable for X-ray structure analysis were obtained using rare-earth halides as a flux. Tb3Pd2 adopts its own structure type, which can be described as a superstructural derivative of the U3Si2 type, which is the type adopted by Er3Pd2. Compound Er6Co5-x belongs to the Ce6Co2-xSi3 family. All three compounds feature fused tricapped {TR6} (R = rare-earth metal and T = transition metal) trigonal prismatic heterometallic clusters. R3Pd2 is reported to crystallize in the U3Si2 type; however, our more detailed structure analysis reveals that deviations occur with heavier R elements. Similarly, Er6Co5-x was assumed to be stoichiometric Er4Co3 = Er6Co4.5. Our studies reveal that it has a single defective transition-metal site leading to the composition Er6Co4.72(2). LMTO (linear muffin-tin orbital)-based electronic structure calculations suggest the strong domination of heteroatomic bonding in all three structures.

  • 2. Celania, Chris
    et al.
    Smetana, Volodymyr
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Iowa State University, USA.
    Mudring, Anja-Verena
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Iowa State University, USA.
    Bringing order to large-scale disordered complex metal alloys: Gd2Au15-xSbx and BaAuxGa12-x2018In: CrystEngComm, ISSN 1466-8033, E-ISSN 1466-8033, Vol. 20, no 3, p. 348-355Article in journal (Refereed)
    Abstract [en]

    Herein, two new tetragonal complex metallic alloys (CMAs) have been discovered and characterized: Gd2Au15-xSbx [x = 3.0-3.6; I4/mmm; tI34; a = 7.31-7.33 angstrom, c = 14.05-14.11 angstrom; V = 750.2-758 angstrom(3)] and BaAuxGa12-x [x = 3.6-4.4; I4/mcm; tI104; a = 8.77-8.78 angstrom, c = 26.06-26.13 angstrom; V = 2006.5-2010 angstrom(3)]. Both structures incorporate significant anionic site mixing and intricate positional disorder. Gd2Au15-xSbx represents a new structure type with in-plane disordered, but strongly geometrically restricted rhombi motifs. These rhombi connect through additional mixed Au/Sb positions along the c axis; this forms octahedral fragments. BaAuxGa12-x finds its place within the extended NaZn13 structural family, displaying cation-centered snub cubes with empty, distorted icosahedra (allowing for the 1 : 12 ratio) and tetrahedral stars. The split positions order due to geometric constraints to form nets of crown cyclooctane-like sheets in two different conformations. Adjacent planes adopt opposite conformations, forming layers of snub cubes with order between layers, but disorder across the greater structure. The substantial degree of mixing in both structures, together with mutual orientation of the ordered and disordered positions, suggests significant importance of heteroatomic bonding, typically found in polar intermetallic compounds.

  • 3. Celania, Chris
    et al.
    Smetana, Volodymyr
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Iowa State University, USA.
    Mudring, Anja-Verena
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Iowa State University, USA.
    Crystal structures and new perspectives on Y3Au4 and Y(14)Au512017In: Acta crystallographica. Section C, Structural chemistry, ISSN 2053-2296, Vol. 73, p. 692-696Article in journal (Refereed)
    Abstract [en]

    Y3Au4 (triyttrium tetragold) and Y14Au51 (tetradecayttrium henpentacontagold), two binary representatives of Au-rich rare earth (R) systems crystallize with the space groups R (3) over bar and P6/m, adopting the Pu3Pd4 and Gd14Ag51 structure types, respectively (Pearson symbols hR(42) and hP(65)). Avariety of binary R-Au compounds have been reported, although only a few have been investigated thoroughly. Many reports lack information or misinterpret known compounds reported elsewhere. The Pu3Pd4 type is fairly common for group 10 elements Ni, Pd, and Pt, while Au representatives are restricted to just five examples, i.e. Ca3Au4, Pr3Au4, Nd Au-3(4), Gd3Au4, and Th3Au4. Sm6Au7 is suspected to be Sm3Au4 due to identical symmetry and close unit-cell parameters. The Pu3Pd4 structure type allows for full substitution of the position of the rare earth atom by more electronegative and smaller elements, i.e. Ti and Zr. The Gd14Ag51 type instead is more common for the group 11 metals, while rare representatives of group 12 are known. Y3Au4 can be represented as a tunnel structure with encapsulated cations and anionic chains. Though tunnels are present in Y14Au51, this structure is more complex and is best described in terms of polyhedral 'pinwheels' around the tunnel forming polyhedra along the c axis.

  • 4. Celania, Chris
    et al.
    Smetana, Volodymyr
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). U.S. Department of Energy, United States.
    Provino, Alessia
    Manfrinetti, Pietro
    Mudring, Anja-Verena
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). U.S. Department of Energy, United States; Iowa State University, United States.
    R-14(Au, M)(51) (R = Y, La-Nd, Sm-Tb, Ho, Er, Yb, Lu; M = Al, Ga, Ge, In, Sn, Sb, Bi): Stability Ranges and Site Preference in the Gd14Ag51 Structure Type2018In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 18, no 2, p. 993-1001Article in journal (Refereed)
    Abstract [en]

    Twenty new ternary representatives of the Gd14Ag51 structure type have been synthesized within the R-Au-M family (R = Y, La-Nd, Sm-Tb, Ho, Er, Yb, Lu; M = Al, Ga, Ge, Sn, Sb, Bi) using solid state synthesis techniques. The list of post transition metals (M) involved in the formation of this type of structure could be augmented by five new representatives. All compounds crystallize in the hexagonal space group P6/m (#175) with the unit cell ranges of a = 12.3136(2)-12.918(1) angstrom and c = 8.9967(3)-9.385(1) angstrom, and incorporate different degrees of Au/M mixing. The involvement of the post transition element in the structure varies from one to another compound both qualitatively and quantitatively. A rather significant phase width can be expected for the majority of compounds, however, not without exclusions. The distribution of the post transition metals within the structure has been analyzed via single crystal X-ray diffraction. While the positional disorder of one near-origin Au position is expectable for all compounds due to steric reasons, two specimens show an obvious deviation from the others including another Au position split along the c axis. Possible factors affecting this behavior are discussed.

  • 5. Di Marcantonio, M.
    et al.
    Namanga, J. E.
    Smetana, Volodymyr
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Gerlitzki, N.
    Vollkommer, F.
    Mudring, Anja-Verena
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bacher, G.
    Nannen, E.
    Green-yellow emitting hybrid light emitting electrochemical cell2017In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 5, no 46, p. 12062-12068Article in journal (Refereed)
    Abstract [en]

    Light-emitting electrochemical cells (LECs) are attractive candidates for future low-cost lighting applications such as light-emitting smart tags, thanks to their simplicity, fully solution-based fabrication and flexibility. However, high brightness and efficiency in combination with satisfactory operation lifetimes need to be achieved for different emission colours bearing future device commercialization in mind. LECs emitting in the yellow-green spectral range, where the human eye is most sensitive are thereby particularly attractive. Here we present an improved hybrid LEC based on an Ir-iTMC, [Ir(4-Fppy)(2)(pbpy)][PF6] (4-Fppy = 2-(4-fluorophenyl) pyridinato, pbpy = 6-phenyl-2,2'-bipyridine) emitting at 557 nm. It features a luminance of 2400 cd m(-2) when driven at a constant voltage of 4 V, and a lifetime of 271 h at a luminance of 1500 cd m(-2) under pulsed current operation. The hybrid LEC shows an enhanced performance compared to a LEC solely based on the Ir-ITMC where operation lifetimes of 165 h at a luminance above 1200 cd m(-2) under pulsed current operation conditions were observed. The performance improvement was achieved by addition of a solution-processed ZnO nanoparticle film on top.

  • 6. Li, Min
    et al.
    Smetana, Volodymyr
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Iowa State University, USA.
    Wilk-Kozubek, Magdalena
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Iowa State University, USA; Wrocław Research Centre EIT+, Poland.
    Mudryk, Yaroslav
    Alammar, Tarek
    Pecharsky, Vitalij K.
    Mudring, Anja-Verena
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Iowa State University, USA.
    Open-Framework Manganese(II) and Cobalt(II) Borophosphates with Helical Chains: Structures, Magnetic, and Luminescent Properties2017In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 56, no 18, p. 11104-11112Article in journal (Refereed)
    Abstract [en]

    Two borophosphates, (NH4)(1-2x)M1+x(H2O)(2)(BP2O8)center dot yH(2)O with M = Mn (I) and Co (II), synthesized hydrothermally crystallize in enantiomorphous space groups P6(5)22 and P6(1)22 with a = 9.6559(3) and 9.501(3) angstrom, c = 15.7939(6) and 15.582(4) angstrom, and V = 1275.3(1) and 1218.2(8) angstrom(3) for I and II, respectively. Both compounds feature helical chains composed of vertex-sharing tetrahedral PO4 and BO4 groups that are connected through O atoms to transition-metal cations, Mn2+ and Co2+, respectively. For the two crystallographically distinct-transition-metal cation sites present in the structure, this results in octahedral coordination with different degrees of distortion from the ideal symmetry. The crystal-field parameters, calculated from the corresponding absorption spectra, indicate that Mn2+ and Co2+ ions are located in a weak octahedral-like crystal field and suggest that the Co-ligand interactions are more covalent than the Mn-ligand ones. Luminescence measurements at room temperature reveal an orange emission that red-shifts upon lowering of the temperature to 77 K for I, while II is not luminescent. The luminescence lifetimes of I are 33.4 mu s at room temperature and 1.87 ms at 77 K. Both compounds are Curie-Weiss paramagnets with negative Weiss constants and effective magnetic moments expected for noninteracting Mn2+ and Co2+ cations but no clear long-range magnetic order above 2 K.

  • 7. Liu, J.
    et al.
    Mudryk, Y.
    Smetana, Volodymyr
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Iowa State University, USA.
    Mudring, Anja-Verena
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Iowa State University, USA.
    Pecharsky, V. K.
    Anomalous effects of Sc substitution and processing on magnetism and structure of (Gd1-xScx)(5)Ge-42019In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 474, p. 482-492Article in journal (Refereed)
    Abstract [en]

    The kinetic arrest observed in the parent Gd5Ge4 gradually vanishes when a small fraction (x = 0.025, 0.05 and 0.10) of Gd is replaced by Sc in (Gd1-xScx)(5)Ge-4, and the magnetic ground state changes from antiferromagnetic (AFM) to ferromagnetic (FM). A first order phase transition coupled with the FM-AFM transition occurs at T-C = 41 K for x = 0.05 and at T-C = 53 K for x = 0.10 during heating in applied magnetic field of 1 kOe, and the thermal hysteresis is near 10 K. The first-order magnetic transition is coupled with the structural Sm5Ge4-type to Gd5Si4-type transformation. The magnetization measured as a function of applied magnetic field shows sharp metamagnetic-like behavior. At the same time, the AFM to paramagnetic transition in (Gd1-xScx)(5)Ge-4 with x = 0.10, is uncharacteristically broad indicating development of strong short-range AFM correlations above the Ned temperature. Comparison of the magnetization data of bulk, powdered, and metal-varnish composite samples of (Gd0.95Sc0.05)(5)Ge-4 shows that mechanical grinding and fabrication of a composite have little effect on the temperature of the first-order transformation, but short-range ordering and AFM/FM ratio below T-C are surprisingly strongly affected.

  • 8. Namanga, Jude E.
    et al.
    Gerlitzki, Niels
    Smetana, Volodymyr
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). U.S. Department of Energy, United States.
    Mudring, Anja-Verena
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Ruhr-Universität Bochum, Germany; U.S. Department of Energy, United States.
    Supramolecularly Caged Green-Emitting Ionic Ir(III)-Based Complex with Fluorinated CN Ligands and Its Application in Light-Emitting Electrochemical Cells2018In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, no 13, p. 11026-11036Article in journal (Refereed)
    Abstract [en]

    Ionic Ir(III) complexes are the most promising emitters in light emitting electrochemical cells (LECs), especially in the high energy emission range for which it is difficult to find emitters with sufficient efficiencies and lifetimes. To overcome this challenge, we introduced the concept of intramolecular pi-pi stacking of an ancillary ligand (6-phenyl-2,2'-bipyridine, pbpy) in the design of a new green-emitting iridium ionic transition metal complex with a fluoro-substituted cyclometallated ligand, 2-(4-fluorophenyOpyridinato (4Fppy). [Ir(4Fppy)(2)(pbpy)][PF6] has been synthesized and characterized and its photophysical and electrochemical properties have been studied. The complex emits green light with maxima at 561 and 556 nm under UV excitation from powder and thin film, respectively, and displays a high photoluminescence quantum yield (PLQY) of 78.5%. [Ir(4Fppy)(2)(pbpy)][PF6] based LECs driven under pulsed current conditions showed under an average current density of 100 A m(-2) (at 50% duty cycle) a maximum luminance of 1443 cd m(-2), resulting in 14.4 cd A(-1) and 7.4 lm W-1 current and power efficiencies, respectively. A remarkable long device lifetime of 214 h was observed. Reducing the average current density to 18.5 A m(-2) (at 75% duty cycle) led to an exceptional device performance of 19.3 cd A(-1) and 14.4 lm W1- for current and power efficiencies, an initial maximum luminance of 352 cd m(-2) and a lifetime of 617 h.

  • 9. Rhodehouse, Melissa L.
    et al.
    Bell, Thomas
    Smetana, Volodymyr
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). USDOE, United States.
    Mudring, Anja-Verena
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). USDOE, United States; Iowa State University, United States.
    Meyer, Gerd H.
    An Obscured or Nonexistent Binary Intermetallic, Co7Pr17, Its Existent Neighbor Co2Pr5, and Two New Ternaries in the System Co/Sn/Pr, CoSn3Pr1-x, and Co2-xSn7Pr32018In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 18, no 10, p. 6273-6283Article in journal (Refereed)
    Abstract [en]

    Four compounds are reported in this study. Co7Pr17 (10, cP96, P2(1)3, a = 13.4147(8) angstrom, Z = 4), either nonexistent or obscured in the Co/Pr phase diagram, has been obtained from a PrBr3 flux. With 29.2 mol % Co, it is close to Co2Pr5 (28.6 mol % Co, 2, C2Mn5 type of structure, mC28, C2/c, a = 16.5471(7) angstrom, b = 6.5107(3) angstrom, c = 7.1067(3) angstrom, beta = 96.230(3)degrees, Z = 4), existent in the Co/Pr phase diagram, produced by arc-melting of a stoichiometric mixture of the metals. The addition of the reactive metal tin to Co/Pr mixtures yielded two new ternary polar intermetallics, CoSn3Pr1-x (x = 0.04, 11, RuSn3La type, cP40, Pm(3) over barn, a = 9.587(3) angstrom, Z = 8) and Co2-xSn7Pr3 (x = 0.78, 12, Ni2-xSn7-yCe3 type, oC24, Cmmm, a = 4.5043(4) angstrom, b = 27.227(2) angstrom, c = 4.5444(3) angstrom, Z = 2). Electronic structure calculations reveal extensive heteroatomic Co-Pr interactions in the binaries with little homoatomic contributions. With tin as the third component in the ternaries, heteroatomic Co-Sn and Sn-Pr bonding interactions are dominant, following the sequence of coordination spheres around Co.

  • 10. Rhodehouse, Melissa L.
    et al.
    Bell, Thomas
    Smetana, Volodyrnyr
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Iowa State University, United States.
    Mudring, Anja-Verena
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Iowa State University, United States.
    Meyer, Gerd H.
    From the Nonexistent Polar Intermetallic Pt3Pr4 via Pt2-xPr3 to Pt/Sn/Pr Ternaries2018In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 57, no 16, p. 9949-9961Article in journal (Refereed)
    Abstract [en]

    Although the Pt-Pr phase diagram has been explored well, recent work on rare-earth metal cluster halides with endohedral transition metal atoms has provided a new binary intermetallic that is nonexistent in the known phase diagram: The binary Pt3Pr4 (1) crystallizes in a new structure type (mP56, P21/c, a = 12.353(2) angstrom, b = 7.4837(9) angstrom, c = 17.279(2) angstrom, beta = 118.003(7)degrees, z = 8) With six crystallographically independent Pt as well as eight Pr positions. The subsequent detailed investigation has led to another previously unreported, binary phase with the Ga2Gd3 structure type, Pt2-xPr3 (2, tI80, I4/mcm, a = 11.931(9) A, c = 14.45(1) angstrom, z = 16), that is practically overlapping with the rhombohedral Pt2Pr3 existing in the phase diagram. Application of different tin containing fluxes to reproduce the newly detected phases brought about two almost iso-compositional temary compounds with Sn, Pt4Sn6Pr2.91 (3), and Pt4.Sn6Pr3 (4), as well as Pt12Sn24Pr4.84 (5). 3 is a representative of the Pt4Ge6Ce3 type (oP52, Pnma, a = 7.2863(3) A, b = 4.4909(2) angstrom, c = 35.114(2) angstrom), while 4 represents a new variant of the prolific T4E6R3 family (T = transition metal, E = main group (semOrnetal, R = rare-earth metal; Pt4Sn6Pr3: oP52, Pnma, a = 27.623(1) angstrom, b = 4.5958(2) A, c = 9.3499(5) A). Pt(12)sn(24)Prs_x (5) crystallizes as a variant of the Ni8Sn16Gd3 type (cI82, /m(-3), a = 12.274(1) A, z = 2). Electronic structure calculations provide hints on the origin of the structural changes (pseudo-polymorphism) for PtxPr3 with x = 1.97 and 2.00, respectively, and reveal that heteroatomic Pt-Pr bonding strongly dominates in both binaries while the addition of the reactive metal tin leads to dominating Pt-Sn bonding interactions in the ternaries; Pt Pt bonding interactions are strong but represent a minority in the binaries and are not present at all in the ternaries.

  • 11. Sangeetha, N. S.
    et al.
    Anand, V. K.
    Cuervo-Reyes, Eduardo
    Smetana, Volodymyr
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mudring, Anja-Verena
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Johnston, D. C.
    Enhanced moments of Eu in single crystals of the metallic helical antiferromagnet EuCo2-yAs22018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 14Article in journal (Refereed)
    Abstract [en]

    The compound EuCo2-yAs2 with the tetragonal ThCr2Si2 structure is known to contain Eu+2 ions with spin S = 7/2 that order below a temperature T-N approximate to 47 K into an antiferromagnetic (AFM) proper helical structure with the ordered moments aligned in the tetragonal ab plane, perpendicular to the helix axis along the c axis, with no contribution from the Co atoms. Here we carry out a detailed investigation of the properties of single crystals. We consistently find about 5% vacancies on the Co site from energy-dispersive x-ray analysis and x-ray diffraction refinements. Enhanced ordered and effective moments of the Eu spins are found in most of our crystals. Electronic structure calculations indicate that the enhanced moments arise from polarization of the d bands, as occurs in ferromagnetic Gd metal. Electrical resistivity measurements indicate metallic behavior. The low-field in-plane magnetic susceptibilities x(ab) (T < T-N) for several crystals are reported that are fitted well by unified molecular field theory (MFT), and the Eu-Eu exchange interactions J(ij) are extracted from the fits. High-field magnetization M data for magnetic fields H parallel to ab reveal what appears to be a first-order spin-flop transition followed at higher field by a second-order metamagnetic transition of unknown origin, and then by another second-order transition to the paramagnetic (PM) state. For H parallel to c, the magnetization shows only a second-order transition from the canted AFM to the PM state, as expected. The critical fields for the AFM to PM transition are in approximate agreement with the predictions of MFT. Heat capacity C-p measurements in zero and high H are reported. Phase diagrams for H parallel to c and H parallel to ab versus T are constructed from the high-field M(H, T) and C-p(H, T) measurements. The magnetic part C-mag(T, H = 0) of C-p(T, H = 0) is extracted and is fitted rather well below T-N by MFT, although dynamic short-range AFM order is apparent in Cmag(T) up to about 70 K, where the molar entropy attains its high-T limit of R ln 8.

  • 12. Sangeetha, N. S.
    et al.
    Smetana, Volodymyr
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mudring, Anja-Verena
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Johnston, D. C.
    Antiferromagnetism in semiconducting SrMn2Sb2 and BaMn2Sb2 single crystals2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 1, article id 014402Article in journal (Refereed)
    Abstract [en]

    Crystals of SrMn2Sb2 and BaMn2Sb2 were grown using Sn flux and characterized by powder and single-crystal x-ray diffraction, respectively, and by single-crystal electrical resistivity rho, heat capacity C-p, and magnetic susceptibility chi measurements versus temperature T, and magnetization versus field M(H) isotherm measurements. SrMn2Sb2 adopts the trigonal CaAl2Si2-type structure whereas BaMn2Sb2 crystallizes in the tetragonal ThCr2Si2-type structure. The rho(T) data indicate semiconducting behaviors for both compounds with activation energies of greater than or similar to 0.35 eV for SrMn2Sb2 and 0.16 eV for BaMn2Sb2. The chi(T) and C-p(T) data reveal antiferromagnetic (AFM) ordering at T-N = 110 K for SrMn2Sb2 and 450 K for BaMn2Sb2. The anisotropic chi(T <= T-N) data also show that the ordered moments in SrMn2Sb2 are aligned in the hexagonal ab plane whereas the ordered moments in BaMn2Sb2 are aligned collinearly along the tetragonal c axis. The ab-plane M(H) data for SrMn2Sb2 exhibit a continuous metamagnetic transition at low fields 0 < H less than or similar to 1 T, whereas BaMn2Sb2 exhibits no metamagnetic transitions up to 5.5 T. The chi(T) and C-p(T) data for SrMn2Sb2 and BaMn2Sb2 indicate strong dynamic short-range AFM correlations above their respective TN up to at least 900 K within a local-moment picture, corresponding to quasi-two-dimensional magnetic behavior. The present results and a survey of the literature for Mn pnictides with the CaAl2Si2 and ThCr2Si2 crystal structures show that the T-N values for the CaAl2Si2-type compounds are much smaller than those for the ThCr2Si2-type materials.

  • 13.
    Smetana, Volodymyr
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mudryk, Yaroslav
    Pecharsky, Vitalij K.
    Mudring, Anja-Verena
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Controlling magnetism via transition metal exchange in the series of intermetallics Eu(T1, T2)(5)In (T = Cu, Ag, Au)2018In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 6, no 6, p. 1353-1362Article in journal (Refereed)
    Abstract [en]

    Three series of intermetallic compounds Eu(T1, T2)(5)In (T = Cu, Ag, Au) have been investigated over their full compositional ranges. Single crystals of all compounds have been obtained by self-flux and were analyzed by single crystal X-ray diffraction revealing that the representatives fall into two structure types: CeCu6 (oP28, Pnma, a = 8.832(3)-9.121(2) angstrom, b = 5.306(2)-5.645(1) angstrom, c = 11.059(4)-11.437(3) angstrom, V = 518.3(3)-588.9(2) angstrom(3)) and YbMo2Al4 (t/14, /4/mmm, a = 7.139(2)-7.199(2) angstrom, c = 5.417(3)-5.508(1) angstrom, V = 276.1(2)-285.8(1) angstrom(3)). The structural preference was found to depend on the cation/anion size ratio, while the positional preference within the CeCu6 type structure shows an apparent correlation with the anion size. Chemical compression, hence, a change in cell volume, which occurs upon anion substitution, appears to be the main driving force for the change of magnetic ordering. While EuAg5In shows antiferromagnetic behavior at low temperatures, mixing Cu and Au within the same type of structure results in considerable changes in the magnetism. The Eu(Cu, Au)(5)In alloys with CeCu6 structure show complex magnetic behaviors and a strong magnetic field-induced spin-reorientation transition with the critical field of the transition being dependent on Cu/Au ratio. The alloys adopting the YbMo2Al4 type structure are ferromagnets exhibiting unusually high magnetic moments. The heat capacity of EuAu2.66Cu2.34In reveals a double-peak structure evolving with the magnetic field. However, low-temperature X-ray powder diffraction does not show a structural transition.

  • 14.
    Smetana, Volodymyr
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Iowa State University, United States.
    Rhodehouse, Melissa
    Meyer, Gerd
    Mudring, Anja-Verena
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Iowa State University, United States.
    Gold Polar Intermetallics: Structural Versatility through Exclusive Bonding Motifs2017In: Accounts of Chemical Research, ISSN 0001-4842, E-ISSN 1520-4898, Vol. 50, no 11, p. 2633-2641Article, review/survey (Refereed)
    Abstract [en]

    The design of new materials with desired chemical and physical characteristics requires thorough understanding of the underlying composition structure property relationships and the experimental possibility of their modification through the controlled involvement of new components. From this point of view, intermetallic phases, a class of compounds formed by two or more metals, present an endless field of combinations that produce several chemical compound classes ranging from simple alloys to true ionic compounds. Polar intermetallics (PICs) belong to the class that is electronically situated in the middle, between Hume-Rothery phases and Zintl compounds and possessing e/a (valence electron per atom) values around 2. In contrast to the latter, where logical rules of formation and classification systems were developed decades ago, polar intermetallics remain a dark horse with a huge diversity of crystal structures but unclear mechanisms of their formation. Partial incorporation of structural and bonding features from both nonpolar and Zintl compounds is commonly observed here. A decent number of PICs can be described in terms of complex metallic alloys (CMAs) following the Hume-Rothery electron-counting schemes but exhibit electronic structure changes that cannot be explained by the latter. Our research is aimed at the discovery and synthesis of new polar intermetallic compounds, their structural characterization, and investigation of their properties in line with the analysis of the principles connecting all of these components. Understanding of the basic structural tendencies is one of the most anticipated outcomes of this analysis, and systematization of the available knowledge is the initial and most important step.

    In this Account, we focus on a well-represented but rather small section of PICs: ternary intermetallic compounds of gold with electropositive and post-transition metals of groups 12 to 15. The strong influence of relativistic effects in its chemical bonding results in special, frequently unique structural motifs, while at the same time gold participates in common structure types as an ordinary transition element. Enhanced bonding strength leads to the formation and stabilization of complex homo-and heteroatomic clusters and networks that are compositionally restricted to just a few options throughout the periodic table. Because it has the highest absolute electronegativity among metals, comparable to those of some halogens, gold usually plays the role of an anion, even being able to form true salts with the most electropositive metals. We discuss the occurrence of the structure types and show the place of gold intermetallics in the general picture. Among the structures considered are ones as common as AIB(2) or BaAl4 types, in line with the recently discovered diamond-like homoatomic metal networks, formation of local fivefold symmetry, different types of tunneled structures, and more complex intergrown multicomponent structures.

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