The structural chemistry of Li3Zn2MO6 (M=Sb, Bi) and related phases

Abstract The partial replacement of Li + ions in Li 7 MO 6 (M=Sb, Bi) by Zn 2+ ions has been investigated. New phases of composition Li 3 Zn 2 MO 6 have been synthesised and their structures shown by powder neutron diffraction to contain cubic close-packed oxygen ions with all the octahedral sites occupied in an ordered fashion by the cations. This is in marked contrast to the structure of the Li 7 MO 6 compounds, which has hexagonal close-packing with six of the seven Li + ions in tetrahedral coordination. The new compounds exhibit a degree of nonstoichiometry, since the Li:Zn ratio may be increased whilst retaining a total of six cations in the formula. Vacancies, which are introduced on the oxygen sublattice to maintain charge balance, result in a typical composition Li 3.5 Zn 1.5 MO 5.75 . The Li + conductivities are lower than those observed for the Li 7 MO 6 phases (1.1×10 −5 ohm −1 cm −1 at 300°C for Li 3.5 Zn 1.5 BiO 5.75 ), due to the absence of cation vacancies.