The relationships between phases and structures of lithium manganese spinels

Structures of the cubic lithium manganese spinels synthesized at 900°C, and the tetragonal spinel synthesized by quenching from 920°C into liquid N2 were determined by time-of-flight (TOF) neutron powder diffraction. The ionic distribution was determined for the tetragonal spinel to be [Li1]tetra(Mn2)octaO3.86(3). A small amount of oxygen vacancy was observed at the oxygen site. On the other hand, the structure of the cubic spinel determined at 325 K showed oxygen vacancy at 32e site with interstitial oxygen at 8b sites. The occupation parameters at the interstitial 8b site decreased with decreasing synthesis temperature from 900° to 750°C. On the basis of these findings a new oxygen vacancy cluster model is proposed.