Order-disorder transition in the complex lithium spinel Li2CoTi3O8

Li2CoTi3O8 has an ordered Li2BB'O-3(8) spinel structure, space group P4(3)32, at room temperature with 3:1 ordering of Ti and Li on the octahedral sites, and Li, Co disordered over the tetrahedral site. Rietveld refinement of variable temperature neutron powder diffraction data has shown an order-disorder phase transition in Li2CoTi3O8 which commences at similar to 500 degrees C with Li and Co mixing on the tetrahedral and 4-fold octahedral sites and is complete at a first order structural discontinuity at similar to 915 degrees C. The fraction of Ti on the 12-fold octahedral site exhibits a small decrease with increasing temperature, which may suggest that the disordering involves all three cations. Above 930 degrees C, the structure, space group Fd (3) over barm, has Li, Co and Ti sharing a single-octahedral site and Li, Co sharing a tetrahedral site, although Co still exhibits a preference for tetrahedral coordination. A labelling scheme for ordered and partially ordered 3:1 spinels is devised which focuses on the occupancy of the Li,B cations. (c) 2007 Elsevier Inc. All rights reserved.