Neutron diffraction investigation of the cationic distribution in the structure of the spinel-type solid solutions Li2−2xM1+xCl4 (M = Mg, V): Correlation with the ionic conductivity and NMR data

The structure of the spinel-type solid solutions Li2−2xMin1+xCl4 M = Mg, V has been studied by neutron diffraction. The cationic distribution in the stoichiometric phases Li2MgC14 and Li2 VCl4 is inverse at room temperature, but some vacancies tend to appear in the tetrahedral 8(a) sites. With increasing temperature a gradual migration of the Li+ ions from the 8(a) positions into the octahedral 16(c) ones has been established for Li2MgCl4. The extra vacancies in the highly deficient spinels LiMgCl3 and LiVCl3 (x = 13) have been found to be located in the tetrahedral 8(a) sites only. The correlation between the thermal evolutiomn of the cationic dustribution and the corresponding conductivity and NMR data gives a satisfying interpretation of the jump mechanisms responsible for the high ionic mobility in these materials.