Oxygen nonstoichiometry in Li-Mn-O spinel oxides: A powder neutron diffraction study

Neutron powder diffraction has been carried out on two series of Li-Mn-O samples with spinel structure, which have been shown to lose oxygen with respect to initial stoichiometric spinels: (i) Li1.05Mn2O4 quenched from 800 or 925 degrees C, (ii) ((Li1.33Mn1.67O4)) (nominal) treated with ammonia gas at 200 degrees C, The structural refinements unambiguously show that both 925 degrees C quenching and low-temperature ammonia treatment induce oxygen vacancies in the spinel lattice, However, the mechanism of oxygen loss is markedly different between quenchings at 800 and 925 degrees C, While the latter actually corresponds to the introduction of anionic vacancies at constant cation composition, the former is due to a rearrangement of the Li/Mn ratio in the spinel phase and the formation of an additional lithium-rich phase Li2MnO3. The presence of vacancies induce a significant increase in atomic displacement parameters of oxygen. (C) 1998 Academic Press.