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Home  >  Journal list  >  MATERIALS TRANSACTIONS  >  Vol.45  No.7 (2004)  >  pp.2048-2055

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Phase Transitions and Low-temperature Structure of Lithium Manganese Oxide Spinel

Masao Yonemura1)2), Takashi Kamiyama3), Yoji Kawamoto2) and Ryoji Kanno1)
1) Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology
2) Department of Chemistry, Faculty of Science, Kobe University
3) Neutron Science laboratory, Institute of Materials Structure Science, High Energy Accelerator Research Organization

Low-temperature structures of the lithium manganese spinels were determined using TOF neutron Rietveld analysis. The spinels LiMn2O4-δ with different δ values, (0.016, 0.040, and 0.132) showed the cubic-orthorhombic phase transitions, and the lattice distortion decreased with decreasing δ. Although no anomaly corresponding to the cubic-orthorhombic phase transition was observed in the DSC curve for the spinel with δ ∼ 0.016, the transition was observed by the structure analysis, which is consistent with the broad Cp anomaly at 250 K. The cubic-orthorhombic phase transition is closely correlated to the existence of the vacancy. The charge disproportionation into trivalent and tetravalent state proceeds gradually with decreasing temperature, and the extent of the disproportionation is dependent on the vacancy. Based on the structure analysis, the phase transitions in the spinel are discussed.

lithium manganese spinel, phase transition, charge-ordering

Received: February 04, 2004
Accepted: April 15, 2004 , Published online: June 24, 2005
Copyright (c) 2005 The Japan Institute of Metals



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