Crystal Structures of Double Vanadates LiCoVO 4 and Li 0.5 Co 1.25 VO 4

Abstract

The crystal structures of vanadates Li1-2xCo1+xVO4 with x = 0 and 0.25 have been studied by a full pattern analysis. It has been shown that in cubic spinel LiCoVO4 (space group Fd3m), the 8a tetrahedral sites contain a majority of vanadium and a small amount of lithium; all cobalt, lithium, and a small amount of vanadium occupy the 16d octahedral sites. Li0.5Co1.25VO4 crystals belong to the rhombic system (Imma space group) with unit cell parameters a = 5.939(1)A, b = 5.810(1)A, and c = 8.303(1)A. On substitution of lithium by cobalt according to the scheme 2Li+ → Co2+ + □, half of the lithium and 70% of the vacancies formed are in the 4a octahedral sites, and one‐third of lithium and most of cobalt occupy the 4d octahedral sites. The 4e tetrahedral sites are completely occupied by vanadium and lithium in a ratio of 0.92/0.08. The interatomic distances in LiCoVO4 and Li0.5Co1.25VO4 are calculated, and the sizes of lithium ion transport channels are evaluated.