Order-disorder transition in the complex lithium spinel Li2CoTi3O8 |
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Authors: | Nik Reeves Denis Pasero Anthony R. West |
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Affiliation: | Department of Engineering Materials, The University of Sheffield, Mappin Street, Sheffield, S1 3JD, UK |
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Abstract: | Li2CoTi3O8 has an ordered Li2BB′3O8 spinel structure, space group P4332, 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 ∼500 °C with Li and Co mixing on the tetrahedral and 4-fold octahedral sites and is complete at a first order structural discontinuity at ∼915 °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 °C, the structure, space group Fd3¯m, 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. |
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Keywords: | Spinels Ordered spinels Cation ordering Crystal structures Neutron powder diffraction Order-disorder Phase transition |
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