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X-ray absorption spectroscopy on layered cobaltates NaxCoO2

T. Kroll, M. Knupfer, J. Geck, C. Hess, T. Schwieger, G. Krabbes, C. Sekar, D. R. Batchelor, H. Berger, B. Buechner

cond-mat.str-elarXiv:cond-mat/0606518

Abstract

Measurements of polarization and temperature dependent soft x-ray absorption have been performed on NaxCoO2 single crystals with x=0.4 and x=0.6. They show a deviation of the local trigonal symmetry of the CoO6 octahedra, which is temperature independent in a temperature range between 25 K and 372 K. This deviation was found to be different for Co3+ and Co4+ sites. With the help of a cluster calculation we are able to interpret the Co L23-edge absorption spectrum and find a doping dependent energy splitting between the t2g and the eg levels (10Dq) in NaxCoO2.

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