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 d0 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 d0 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 d0 transition metal−oxide bonds needs to either be terminal or should link to another d0 transition metal. With respect to the direction of the out-of-center distortion, Ti4+, V5+, and Nb5+ usually displace toward an edge (local C2 direction) or corner (local C4 direction), whereas Mo6+ and W6+ are observed distorting toward an edge (C2) or face (local C3 direction). Finally, the magnitude of the distortion scales as Mo6+ > V5+ > W6+ > Nb5+ > Ta5+ > Ti4+.