Abstract
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) Li1.05Mn2O4quenched from 800 or 925°C, (ii) “Li1.33Mn1.67O4” (nominal) treated with ammonia gas at 200°C. The structural refinements unambiguously show that both 925°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°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.
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