Diffusion of Li atoms in LiMn2O4 - A structural point of view -
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- ISHIZAWA Nobuo
- Nagoya Institute of Technology
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- TATEISHI Kenji
- Gifu Prefectural Ceramics Research Institute
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The structure of LiMn2O4, its phase transition at around 290 K, and the diffusion mechanism of Li are discussed based on the recent synchrotron X-ray diffraction and molecular dynamics simulation studies. The high-temperature modification (cubic Fd 3m) is essentially of spinel-type containing various types of disorder; (1) the Li atoms are not located exactly at the tetrahedral 8a sites, but mainly distributed among four positions 0.14 Å apart from 8a, (2) some portion of Li atoms are further displaced toward the 16c octahedral interstices with a notable accumulation at the positions 0.35 Å apart from 16c, and (3) the O atoms also show a statistical distribution around their ideal 32e sites. The low-temperature modification adopts a 3 × 3 × 1 superstructure (orthorhombic Fddd) with respect to the high-temperature modification. The bond-length fluctuation has been observed along the pseudo-tetragonal Jahn-Teller distortion direction parallel to the a axis in the heterocubane Mn24O94 cluster. The four Mn2 atoms in the heterocubane presumably shares three electrons in the e-parentage low-energy-level orbitals by the double-exchange Zener mechanism. The time-averaged oxidation state for Mn2 is estimated to be +3.25. The heterocubane Zener polarons are isolated with each other and embedded in an ordered way in the charge-ordered matrix containing Mn1III, Mn3III, Mn4IV and Mn5IV. Two kinds of diffusion mechanisms for Li atoms are proposed for the high-temperature modification from the molecular dynamics simulation. One is a microscopic version of the classical picture for diffusion based on the concentration difference in diffusion species. This mechanism requires an activation energy of ca. 0.25 eV to jump over a saddle point at the bottleneck. The other mechanism is a diffusion accompanied by the local lattice distortion coupled with the 3d electron transfer between a pair of nearby Mn atoms. This requires no activation energy for Li to pass through the bottleneck. The valence exchange between +3 and +4 in the neighboring Mn pair prompts the displacement of coordinating O atoms along the pseudo-tetragonal Jahn-Teller distortion direction, which presumably plays a principal role in opening the bottleneck of oxygen triangle along the diffusion pathway.
収録刊行物
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- Journal of the Ceramic Society of Japan
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Journal of the Ceramic Society of Japan 117 (1361), 6-14, 2009
公益社団法人 日本セラミックス協会
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詳細情報 詳細情報について
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- CRID
- 1390001205283921664
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- NII論文ID
- 110007026730
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- NII書誌ID
- AA12229489
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- ISSN
- 13486535
- 18820743
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- NDL書誌ID
- 9751571
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- 本文言語コード
- en
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- データソース種別
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- JaLC
- NDL
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- 抄録ライセンスフラグ
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