Preparation of the ordered perovskite-like compounds Ba 4M 3LiO 12 (M = Ta,Nb): A powder neutron diffraction determination of the structure of Ba 4Ta 3LiO 12

The hexagonal ordered perovskite-like compounds Ba ₄Ta ₃LiO ₁₂ and Ba ₄Nb ₃LiO ₁₂ have been prepared. The structure of Ba ₄Ta ₃LiO ₁₂ has been determined by profile analysis of a powder neutron diffraction pattern. The structure is based on an eight layer ( ccch) stacking sequence of the BaO ₃ layers (space group {P6 ₃}/{mmc}) with the lithium atoms confined to the face-shared octahedral sites. The relationship of this structure to that of Ba ₅Ta ₄O ₁₅ is discussed.