<i>Anti</i>-Perovskite Li-Battery Cathode Materials

Through single-step solid-state reactions, a series of novel bichalcogenides with the general composition (Li₂Fe)<i>Ch</i>O (<i>Ch</i> = S, Se, Te) are successfully synthesized. (Li₂Fe)<i>Ch</i>O (<i>Ch</i> = S, Se) possess cubic <i>anti</i>-perovskite crystal structures, where Fe and Li are completely disordered on a common crystallographic site (3<i>c</i>). According to Goldschmidt calculations, Li⁺ and Fe²⁺ are too small for their common atomic position and exhibit large thermal displacements in the crystal structure models, implying high cation mobility. Both compounds (Li₂Fe)<i>Ch</i>O (<i>Ch</i> = S, Se) were tested as cathode materials against graphite anodes (single cells); They perform outstandingly at very high charge rates (270 mA g^–1, 80 cycles) and, at a charge rate of 30 mA g^–1, exhibit charge capacities of about 120 mA h g^–1. Compared to highly optimized Li_1–<i>x</i>CoO₂ cathode materials, these novel <i>anti</i>-perovskites are easily produced at cost reductions by up to 95% and, yet, possess a relative specific charge capacity of 75%. Moreover, these iron-based <i>anti</i>-perovskites are comparatively friendly to the environment and (Li₂Fe)<i>Ch</i>O (<i>Ch</i> = S, Se) melt congruently; the latter is advantageous for manufacturing pure materials in large amounts

Synthesis and Characterization of Cs_1–<i>x</i>Ti₂Te₂O (<i>x</i> ≈ 0.2): Electron Doping by Te Resulting in a Layered Metal

Reacting Cs₂O_1.3, TiTe, TiO₂, and Te under inert conditions gives powders of Cs_1–<i>x</i>Ti₂Te₂O (<i>x</i> ≈ 0.2). Small single crystals of the same phase were obtained from a CsCl salt melt in closed ampoules. This cesium dititanium ditelluride oxide (<i>P</i>4/<i>mmm</i>, <i>a</i> = 4.0934(3) Å, <i>c</i> = 8.9504(9) Å) is isostructural to CeCr₂Si₂C and contains layers of face-sharing <i>trans</i>-TiTe₄O₂ octahedra that are separated by Cs. As Ti occupies only one crystallographic site, its average oxidation state is +2.6, for the Cs deficit <i>x</i> = 0.2. The formally intermediate Ti valence state agrees well with the metallic conductivity and temperature-independent paramagnetic behavior. No superconductivity is observed down to 0.1 K in Cs_0.8Ti₂Te₂O, but the fact that this structure type can accommodate Te^2– suggests that electron doping of structurally closely related pnictide oxide superconductors, for example, BaTi₂Bi₂O, might be possible

Crystal Chemistry and Physics of UCd₁₁

In the phase diagram U-Cd, only one compound has been identified so farUCd11 (space group Pm3̅m). Since the discovery of this material, the physical properties of UCd11 have attracted a considerable amount of attention. In particular, its complex magnetic phase diagramas a result of tuning with magnetic field or pressureis not well-understood. From a chemical perspective, a range of lattice parameter values have been reported, suggesting a possibility of a considerable homogeneity range, i.e., UCd11–x. In this work, we perform a simultaneous study of crystallographic features coupled with measurements of physical properties. This work sheds light on the delicate relationship between the intrinsic crystal chemistry and magnetic properties of UCd11

BaGe₆ and BaGe_6‑x: Incommensurately Ordered Vacancies as Electron Traps

We report the high-pressure high-temperature synthesis of the germanium-based framework compounds BaGe₆ (<i>P</i> = 15 GPa, <i>T</i> = 1073 K) and BaGe_6–<i>x</i> (<i>P</i> = 10 GPa, <i>T</i> = 1073 K) which are metastable at ambient conditions. In BaGe_6‑<i>x</i>, partial fragmentation of the BaGe₆ network involves incommensurate modulations of both atomic positions and site occupancy. Bonding analysis in direct space reveals that the defect formation in BaGe_6–<i>x</i> is associated with the establishment of free electron pairs around the defects. In accordance with the electron precise composition of BaGe_6‑<i>x</i> for <i>x</i> = 0.5, physical measurements evidence semiconducting electron transport properties which are combined with low thermal conductivity

Successive Phase Transitions in Fe²⁺ Ladder Compounds Sr₂Fe₃Ch₂O₃ (Ch = S, Se)

Small single crystals of Sr₂Fe₃Ch₂O₃ (Ch = S, Se) have been synthesized by flux methods, and bulk materials have been obtained by solid state reactions. Both compounds are isostructural to the compound Sr₂Co₃S₂O₃ (space group <i>Pbam</i>), which contains a novel hybrid spin ladder: a combination of a 2-leg rectangular ladder and a necklace ladder. The 2-leg ladder acts as a well-defined magnetic entity, while intimate magnetic coupling to the necklace ladder induces three successive phase transitions in the range of 40–120 K in each composition (Ch = S or Se), as revealed by Mössbauer spectroscopy, thermodynamics, and magnetometry. The complex magnetic behaviors can be explained by the unique spin–lattice topology

Anionic Ordering in Ba₁₅V₁₂S₃₄O₃, Affording Three Oxidation States of Vanadium and a Quasi-One-Dimensional Magnetic Lattice

Anionic Ordering in Ba₁₅V₁₂S₃₄O₃, Affording Three Oxidation States of Vanadium and a Quasi-One-Dimensional Magnetic Lattic

BaGe₆ and BaGe_6‑x: Incommensurately Ordered Vacancies as Electron Traps

We report the high-pressure high-temperature synthesis of the germanium-based framework compounds BaGe₆ (<i>P</i> = 15 GPa, <i>T</i> = 1073 K) and BaGe_6–<i>x</i> (<i>P</i> = 10 GPa, <i>T</i> = 1073 K) which are metastable at ambient conditions. In BaGe_6‑<i>x</i>, partial fragmentation of the BaGe₆ network involves incommensurate modulations of both atomic positions and site occupancy. Bonding analysis in direct space reveals that the defect formation in BaGe_6–<i>x</i> is associated with the establishment of free electron pairs around the defects. In accordance with the electron precise composition of BaGe_6‑<i>x</i> for <i>x</i> = 0.5, physical measurements evidence semiconducting electron transport properties which are combined with low thermal conductivity

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

Cluster Formation in the Superconducting Complex Intermetallic Compound Be₂₁Pt₅

ConspectusMaterials with the crystal structure of γ-brass type (Cu₅Zn₈ type) are typical representatives of intermetallic compounds. From the electronic point of view, they are often interpreted using the valence electron concentration approach of Hume–Rothery, developed previously for transition metals. The γ-brass-type phases of the main-group elements are rather rare. The intermetallic compound Be₂₁Pt₅, a new member of this family, was synthesized, and its crystal structure, chemical bonding, and physical properties were characterized.Be₂₁Pt₅ crystallizes in the cubic space group <i>F</i>4̅3<i>m</i> with lattice parameter <i>a</i> = 15.90417(3) Å and 416 atoms per unit cell. From the crystallographic point of view, the binary substance represents a special family of intermetallic compounds called complex metallic alloys (CMA). The crystal structure was solved by a combination of synchrotron and neutron powder diffraction data. Besides the large difference in the scattering power of the components, the structure solution was hampered by the systematic presence of very weak reflections mimicking wrong symmetry. The structural motif of Be₂₁Pt₅ is described as a 2 × 2 × 2 superstructure of the γ-brass structure (Cu₅Zn₈ type) or 6 × 6 × 6 superstructure of the simple bcc structural pattern with distinct distribution of defects. The main building elements of the crystal structure are four types of nested polyhedral units (clusters) with the compositions Be₂₂Pt₄ and Be₂₀Pt₆. Each cluster contains four shells (4 + 4 + 6 + 12 atoms). Clusters with different compositions reveal various occupation of the shells by platinum and beryllium. Polyhedral nested units with the same composition differ by the distance of the shell atoms to the cluster center.Analysis of chemical bonding was made applying the electron localizability approach, a quantum chemical technique operating in real space that is proven to be especially efficient for intermetallic compounds. Evaluations of the calculated electron density and electron localizability indicator (ELI-D) revealed multicenter bonding, being in accordance with the low valence electron count per atom in Be₂₁Pt₅. A new type of atomic interactions in intermetallic compounds, cluster bonds involving 8 or even 14 atoms, is found in the clusters with shorter distances between the shell atoms and the cluster centers. In the remaining clusters, four- and five-center bonds characterize the atomic interactions. Multicluster interactions within the polyhedral nested units and three-center polar intercluster bonds result in a three-dimensional framework resembling the structural pattern of NaCl. Be₂₁Pt₅ is a diamagnetic metal and one of rather rare CMA compounds revealing superconductivity (<i>T</i>_c = 2.06 K)