Structure and superconductivity in ternary systems of compounds

Abstract

A survey of the known high Tc ternary systems of compounds is presented. Special emphasis has been placed on the part played by the crystal structure and bonding in the exhibition of high T~ superconductivity. The superconducting and other physical properties of the ternary borides have been discussed in relatively more detail. Finally, the available guidelines from crystal and solid state chemistry points of view, have been reiterated for a search for new high T, materials.

Hybrid Inorganic−Organic Host−Guest Compounds: Open-Framework Cadmium Oxalates Incorporating Novel Extended Structures of Alkali Halides

“…Accordingly, I could be considered as a super rock-salt arrangement of two types of clusters, [ClCd 6 (C 2 O 4 ) 3 ] 5+ and [Rb(H 2 O) 2 (C 2 O 4 ) 3 ] 5- . This type of arrangement is reminiscent of Chevrel phases 1 Figure showing a single [Cd 6 O 24 ] cluster with the Cl - ions at the center.

2 Structure of I in the ab plane.

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The Role of Valence Electron Concentration in Tuning the Structure, Stability, and Electronic Properties of Mo6S9–xIx Nanowires

“…The VEC/formula unit (fu) of this NW is 18. As the bridge S atoms are weakly bonded with the Mo atoms of the octahedron, we can treat the Mo 6 S 6 octahedron to be effectively isolated with 24 valence electrons [(6 × 6) – (2 × 6) = 24] or slightly less (assuming partial charge transfer to bridge S atoms), and this can explain the stability of the octahedral structure. ,− For the remaining Mo 6 S 12 unit, the VEC is about 12, which is favored by the two triangular structures (VEC = 6 for each) …”

“…Moreover, we correlate the structural stability and electronic properties of the NWs with VEC that has been used to understand the stability of bulk cluster compounds such as (NH 4 ) 2 Mo 3 S 13 nH 2 O and Chevrel phase compounds in which the isolated Mo 3 triangular and Mo 6 octahedral units are present, respectively. 22,23 In other cluster compounds, the clusters can be isolated or fused depending upon the value of VEC. 24−26 According to the Hume−Rothery rule, 27 the stability of complex structures of crystals can be understood using valence electron per atom concept.…”

“…However, here we show that the I atoms prefer the bridge sites up to x = 3 and, subsequently, face capping positions on Mo 6 octahedra for higher values of x . Moreover, we correlate the structural stability and electronic properties of the NWs with VEC that has been used to understand the stability of bulk cluster compounds such as (NH 4 ) 2 Mo 3 S 13 nH 2 O and Chevrel phase compounds in which the isolated Mo 3 triangular and Mo 6 octahedral units are present, respectively. , In other cluster compounds, the clusters can be isolated or fused depending upon the value of VEC. − …”

X-ray absorption spectroscopy insights on the structure anisotropy and charge transfer in Chevrel Phase chalcogenides

“…Since their first synthesis in 1971, 1 Chevrel Phases (CPs), M x Mo 6 T 8 (M = metal; T = S, Se, Te), have demonstrated remarkable properties. Most notably, these properties lend themselves toward the use of CPs as high-temperature superconductors, 2,3 thermoelectrics, 4 multivalent cathode materials, 5–8 and catalysts. 9–11 Indeed, its unique pseudo-molecular structure endows CPs with a high degree of tunability of its electronic structure, including its valence and conduction band positions, band gaps, and orbital interactions with participating species in surface reactions.…”