Downscaling Effect on the Superconductivity of Pd₃Bi₂X₂ (X = S or Se) Nanoparticles Prepared by Microwave-Assisted Polyol Synthesis

Pd₃Bi₂S₂ and Pd₃Bi₂Se₂ have been successfully prepared in the form of nanoparticles with diameters of ∼50 nm by microwave-assisted modified polyol synthesis at low temperatures. The composition and morphology of the samples have been studied by means of powder X-ray diffraction as well as electron microscopy methods, including X-ray intensity mapping on the nanoscale. Superconducting properties of the as-prepared samples have been characterized by electrical resistivity measurements down to low temperatures (∼0.2 K). Deviations from the bulk metallic behavior originating from the submicrometer nature of the samples were registered for both phases. A significant critical-field enhancement up to 1.4 T, i.e., 4 times higher than the value of the bulk material, has been revealed for Pd₃Bi₂Se₂. At the same time, the critical temperature is suppressed to 0.7 K from the bulk value of ∼1 K. A superconducting transition at 0.4 K has been observed in nanocrystalline Pd₃Bi₂S₂. Here, a zero-temperature upper critical field of ∼0.5 T has been estimated. Further, spark plasma-sintered Pd₃Bi₂S₂ and Pd₃Bi₂Se₂ samples have been investigated. Their superconducting properties are found to lie between those of the bulk and nanosized samples

Crystal Structure and Physical Properties of Ternary Phases around the Composition Cu₅Sn₂Se₇ with Tetrahedral Coordination of Atoms

A new monoclinic selenide Cu₅Sn₂Se₇ was synthesized, and its crystal and electronic structure as well as thermoelectric properties were studied. The crystal structure of Cu₅Sn₂Se₇ was determined by electron diffraction tomography and refined by full-profile techniques using synchrotron X-ray powder diffraction data: space group <i>C</i>2, <i>a</i> = 12.6509(3) Å, <i>b</i> = 5.6642(2) Å, <i>c</i> = 8.9319(4) Å, β = 98125(4)°, <i>Z</i> = 2; <i>T</i> = 295 K. Thermal analysis and high-temperature synchrotron X-ray diffraction indicated the decomposition of Cu₅Sn₂Se₇ at 800 K with formation of the tetragonal high-temperature phase Cu_4.90(4)Sn_2.10(4)Se₇: space group <i>I</i>4̅2<i>m</i>, <i>a</i> = 5.74738(1) Å, <i>c</i> = 11.45583(3) Å; <i>T</i> = 873 K. Both crystal structures are superstructures to the sphalerite type with tetrahedral coordination of the atoms. In agreement with chemical bonding analysis and band structure calculations, Cu₅Sn₂Se₇ exhibits metal-like electronic transport behavior

Synthesis, Structure, and Properties of Two Zintl Phases around the Composition SrLiAs

Two atomic arrangements were found near the equiatomic composition in the strontium–lithium–arsenic system. Orthorhombic <i>o</i>-SrLiAs was synthesized by reaction of elemental components at 950 °C, followed by annealing at 800 °C and subsequent quenching in water. The hexagonal modification <i>h</i>-SrLi_1–<i>x</i>As was obtained from annealing of <i>o</i>-SrLiAs at 550 °C in dynamic vacuum. The structures of both phases were determined by single-crystal X-ray diffraction: <i>o</i>-SrLiAs, structure type TiNiSi, space group <i>Pnma</i>, Pearson symbol <i>oP</i>12, <i>a</i> = 7.6458(2) Å, <i>b</i> = 4.5158(1) Å, <i>c</i> = 8.0403(3) Å, <i>V</i> = 277.61(2) ų, <i>R</i>_F = 0.028 for 558 reflections; <i>h</i>-SrLi_1–<i>x</i>As, structure type ZrBeSi, space group <i>P</i>6₃/<i>mmc</i>, Pearson symbol <i>hP</i>6, <i>a</i> = 4.49277(9) Å, <i>c</i> = 8.0970(3) Å, <i>V</i> = 141.54(1) ų, <i>R</i>_F = 0.026 for 113 reflections. The analysis of the electron density within the framework of the quantum theory of atoms in molecules revealed a charge transfer according to the Sr^1.3+Li^0.8+As^2.1–, in agreement with the electronegativities of the individual elements. The electron localizability indicator distribution indicated the formation of a 3D anionic framework [LiAs] in <i>o</i>-SrLiAs and a rather 2D anionic framework [LiAs] in <i>h</i>-SrLi_1–<i>x</i>As. Magnetic susceptibility measurements point to a diamagnetic character of both phases, which verifies the calculated electronic density of states

Homo- and Heterovalent Substitutions in the New Clathrates I Si₃₀P₁₆Te_8–<i>x</i>Se_<i>x</i> and Si_30+<i>x</i>P_{16–<i>x</i>}Te_8–<i>x</i>Br_<i>x</i>: Synthesis, Crystal Structure, and Thermoelectric Properties

The new cationic clathrates I Si₃₀P₁₆Te_8–<i>x</i>Se_<i>x</i> and Si_30+<i>x</i>P_{16–<i>x</i>}Te_8–<i>x</i>Br_<i>x</i> were synthesized by the standard ampule technique. The Si₃₀P₁₆Te_8–<i>x</i>Se_<i>x</i> (<i>x</i> = 0–2.3) clathrates crystallize in the cubic space group <i>Pm</i>3̅<i>n</i> with the unit cell parameter <i>a</i> ranging from 9.9382(2) to 9.9696(1) Å. In the case of the Si_30+xP_{16–<i>x</i>}Te_8–<i>x</i>Br_<i>x</i> (<i>x</i> = 1–6.4) clathrates, the lattice parameter varies from 9.9720(8) to 10.0405(1) Å; at lower Si/P ratios (<i>x</i> = 1–3) the ordering of bromine atoms induces the splitting of the guest positions and causes the transformation from the space group <i>Pm</i>3̅<i>n</i> to <i>Pm</i>3̅. Irrespective of the structure peculiarities, the normal temperature motion of the guest atoms inside the oversized cages of the framework is observed. The title clathrates possess very low thermal expansion coefficients ranging from 6.6 × 10^–6 to 1.0 × 10^–5 K^–1 in the temperature range of 298–1100 K. The characteristic Debye temperature is about 490 K. Measurements of the electrical resistivity and thermopower showed typical behavior of <i>p</i>-type thermally activated semiconductors, whereas the temperature behavior of the thermal conductivity is glasslike and in general consistent with the PGEC concept. The highest value of the thermoelectric figure of merit (<i><i>ZT</i></i> = 0.1) was achieved for the Br-bearing clathrate Si_32.1(2)P_13.9(2)Te_6.6(2)Br_1.0(1) at 750 K

Homo- and Heterovalent Substitutions in the New Clathrates I Si₃₀P₁₆Te_8–<i>x</i>Se_<i>x</i> and Si_30+<i>x</i>P_{16–<i>x</i>}Te_8–<i>x</i>Br_<i>x</i>: Synthesis, Crystal Structure, and Thermoelectric Properties

The new cationic clathrates I Si₃₀P₁₆Te_8–<i>x</i>Se_<i>x</i> and Si_30+<i>x</i>P_{16–<i>x</i>}Te_8–<i>x</i>Br_<i>x</i> were synthesized by the standard ampule technique. The Si₃₀P₁₆Te_8–<i>x</i>Se_<i>x</i> (<i>x</i> = 0–2.3) clathrates crystallize in the cubic space group <i>Pm</i>3̅<i>n</i> with the unit cell parameter <i>a</i> ranging from 9.9382(2) to 9.9696(1) Å. In the case of the Si_30+xP_{16–<i>x</i>}Te_8–<i>x</i>Br_<i>x</i> (<i>x</i> = 1–6.4) clathrates, the lattice parameter varies from 9.9720(8) to 10.0405(1) Å; at lower Si/P ratios (<i>x</i> = 1–3) the ordering of bromine atoms induces the splitting of the guest positions and causes the transformation from the space group <i>Pm</i>3̅<i>n</i> to <i>Pm</i>3̅. Irrespective of the structure peculiarities, the normal temperature motion of the guest atoms inside the oversized cages of the framework is observed. The title clathrates possess very low thermal expansion coefficients ranging from 6.6 × 10^–6 to 1.0 × 10^–5 K^–1 in the temperature range of 298–1100 K. The characteristic Debye temperature is about 490 K. Measurements of the electrical resistivity and thermopower showed typical behavior of <i>p</i>-type thermally activated semiconductors, whereas the temperature behavior of the thermal conductivity is glasslike and in general consistent with the PGEC concept. The highest value of the thermoelectric figure of merit (<i><i>ZT</i></i> = 0.1) was achieved for the Br-bearing clathrate Si_32.1(2)P_13.9(2)Te_6.6(2)Br_1.0(1) at 750 K