X-ray absorption spectroscopy studies of Ca_2.9Ln_0.1Co₄O_9+未 (Ln = Ca, Dy, Ho, Er and Lu)

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• 作者：J.L. Chen^a ; Y.S. Liu^a ; Chia-Jyi Liu^b ; N.V. Nong^b ; Y.C. Kao^a ; C.C. Chen^a ; W.C. Wang^a ; S.S. Chen^a ; C.L. Chen^c ; C.L. Dong^d ; C.L. Chang^a ; ^{clchang@mail.tku.edu.tw}
• 关键词：Thermoelectric materials ; X-ray absorption spectroscopy ; Thermoelectric power ; Cobaltite
• 刊名：Journal of Alloys and Compounds
• 出版年：2012
• 期刊代码：45_09258388
• 类别：ms
• 出版时间：15 July, 2012
• 卷：529
• 期：Complete
• 页码：8-11
• 文件大小：676 K

摘要

X-ray absorption near edge structure (XANES) study of Co K-, Co L_2,3-, O K-, and Ca L_2,3-edges on a series of polycrystalline Ca_2.9Ln_0.1Co₄O_9+未 (Ln = Ca, Dy, Ho, Er and Lu) are presented. The high similarity of Co K-edge spectra of the doped and the undoped samples indicate that the average valence of Co is slightly higher than 3+ and it is not varied for different dopants. The variation of the intensity of the Co L_2,3-edge indicates that the number of Co 3d unoccupied states and thermoelectric power shows an opposite trend. According to the O K-edge spectra, the electrical resistivity and Co⁴⁺ 3d-O 2p hybridized unoccupied states also show an opposite trend, which is consistent with our results that a lesser amount of Co⁴⁺ leads to a larger thermoelectric power. There is a monotonic decrease of Ca L_2,3-edge intensity with decreasing ionic radius of the Ln element, which partially substituted for Ca. This could be attributed to a decrease of Ca 3d-O 2p hybridization with decreasing ionic radius of Ln.