The defect structure of a non-stoichiometric spinel which had been prepared under controlled O partial pressures was studied by means of density measurements. Two possible defect models were considered. One was an O-deficient model of the form, (Li)8a[Mn2]16d[O4-δ]32e, and the other was a metal excess model of the form, (Li)8a[Liδ/(4-δ)Mn2δ/(4-δ)]16c[O4]32e. It was expected that the density in the former case would decrease with increasing δ-value, while that in the latter case would increase with increasing δ-value. As the observed density of the non-stoichiometric spinel increased, the metal-excess model was concluded to explain the non-stoichiometry.

M.Hosoya, H.Ikuta, T.Uchida, M.Wakihara: Journal of the Electrochemical Society, 1997, 144[4], L52-4