Cation ordering in the fluorite-like transparent conductors In4+xSn3−2xSbxO12 and In6TeO12

The cation ordering in the fluorite-like transparent conductors In4+xSn3−2xSbxO12 and In6TeO12, was investigated by Time of Flight Neutron Powder Diffraction and X-ray Powder Diffraction (tellurate). The structural results including atomic positions, cation distributions, metal–oxygen distances and metal–oxygen–metal angles point to a progressive cation ordering on both sites of the Tb7O12-type structure with a strong preference of the smaller 4d10 cations (Sn4+, Sb5+, Te6+) for the octahedral sites. The corresponding increase of the overall structure-bonding anisotropy is analyzed in terms of the crystal chemical properties of the OM4 tetrahedral network of the antistructure. The relationships between the M7O12 and the M2O3 bixbyite-type structures are explored. Within the whole series of compositions In4+xM3−xO12 (M=Sn, Sb, Te) there exists an increase of the symmetry gap between the more symmetrical bixbyite structure and the M7O12 type. This is tentatively correlated with the progressive weakening of thermal stability of these compositions from Sn to Te via Sb.