New family of phases, Li2MXO4: X = Zr, Hf; M = Mg, Mn, Fe, Co, Ni, Cu, Zn with α-LiFeO2 and related structures

Abstract Thirteen new phases, Li 2 MXO 4 , have been synthesised. Nine of these, labelled α , with: M = Mg, Mn, Fe, Co, Zn, have the tetragonal α -LiFeO 2 , rock salt-related structure and are isostructural with previously reported Li 2 MgZrO 4 . In their structures, M and X ions are disordered over the octahedral Fe sites of α -LiFeO 2 . Three phases, labelled β , with: MX = NiHf, CuZr, CuHf, have closely related structures but with a lower symmetry space group and significantly different c / a ratios for their tetragonal unit cells. A structural model involving ordering of M and X ions is proposed in which the driving force for ordering is a Jahn-Teller distortion associated with Ni and Cu. Two phases: X = NiHf, NiZr, form other high temperature polymorphs which are also related structurally to rock salt but with varying degrees of cation disorder.