The relationships between phases and structures of lithium manganese spinels

Structures of the cubic lithium manganese spinels synthesized at 900 degree s C; and the tetragonal spinel synthesized by quenching from 920 degrees C into liquid N-2 were determined by rime-of-flight (TOF) neutron powder diff raction. The ionic distribution was determined for the tetragonal spinel to be [Li-1](tetra)(Mn-2)(octa)O-3.86(3). A small amount of oxygen vacancy wa s observed at the oxygen site. On the other hand, the structure of the cubi c spinel determined at 325 K showed oxygen vacancy at 32e site with interst itial oxygen at 8b sites. The occupation parameters at the interstitial 8b site decreased with decreasing synthesis temperature from 900 degrees to 75 0 degrees C. On the basis of these findings a new oxygen vacancy cluster mo del is proposed. (C) 1999 Elsevier Science S.A. All rights reserved.