Cation ordering and order–disorder phase transitionin Co‐substituted Li4Ti5O12 spinels

In this paper we present the results of the synthesis, crystal structure investigations and in situ X-ray diffraction studies of the order-disorder phase transition in cobalt substituted lithium titanate oxide spinels, Li 1.33x Co 2-2x Ti 1+0.67x O 4 (0 ≤ x ≤ 1). Depending on the chemical composition the samples crystallize in two space groups (S.G.): Fd3m (0 ≤ x ≤ 0.40 and x = 1) and P4 3 32 (0.50 ≤ x ≤ 0.875). Samples crystallizing in the S.G. P4 3 32 are ordered spinels with a cation ordering of the 1:3 type at octahedral 4b and 12d sites. The cation ordering in octahedral sites is full in the sample with x = 0.75 (Li and Ti occupy 4b and 12d sites, respectively) and decreases for samples with higher/smaller x. Changes of the extinction conditions and nonlinearities in the concentration dependence of the lattice parameter in the regions 0.40 1173K. The mechanism of the phase transition is based on cation migration.