Li不足型LiMn_2O_4スピネルの合成と構造経時変化

概要

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Spinel-type lithium manganese oxides with lithium-deficient compositions in the atomic ratio range of Li/Mn=y=0.475-0.485 were obtained in a single phase by sintering a mixture of Li_2CO_3 and MnCO_3 at 750℃ in air, followed by quenching into liquid nitrogen. Initially, they were a cubic (Fd3m) compound like the stoichiometric LiMn_2O_4 spinel. However, it was found that the structure turned from cubic to orthorhombic (Fddd) just in storage at room temperature. The change was slow and it took several days or more depending on the sample's composition. The changes in the density, the manganese valence and the weight of the samples accompanied with their structural change were monitored. Those measurements revealed that, though Li-deficient spinels immediately after preparation took a Li (8a)-defective arrangement (Li_xMn_2O_4, x<1), they were gradually changed to a Mn-excess compound (Li_yMn_<2+δ>O_<4-δ> ; y/(2+δ)=x/2, y≤1). It is likely that Jahn-Teller Mn^<3+> ion increased by reduction of the compound generates the structural distortion.
社団法人日本セラミックス協会の論文
2001-06-01