Asymmetric cation coordination in oxide materials:: Influence of lone-pair cations on the intra-octahedral distortion in d0 transition metals

The oxides that contain both a d(0) transition metal (Ti4+, Nb5+, W6+, etc.) and a lone-pair cation (Sn2+, Se4+, Te4+, etc.) are examined to investigate the influence of the lone-pair cation on the intra-octahedral distortion of the d(0) transition metal. The direction and magnitude of the out-of-center distortion are also examined. When an intra-octahedral distortion is observed, at least one of the d(0) transition metal-oxide bonds needs to either be terminal or should link to another d(0) transition metal. With respect to the direction of the out-of-center distortion, Ti4+, V5+, and Nb5+ usually displace toward an edge (local C-2 direction) or corner (local C-4 direction), whereas Mo6+ and W6+ are observed distorting toward an edge (C-2) or face (local C-3 direction). Finally, the magnitude of the distortion scales as Mo6+ > V5+ > W6+ > Nb5+ > Ta5+ > Ti4+.