On the correlation between the X-ray absorption chemical shift and the formal valence state in mixed-valence manganites

Joaquı´n Garcı´a,a * Gloria Subı´as,a Vera Cuarteroa and Javier Herrero-Martinb


a Instituto de Ciencia de Materiales de Arago´n, CSIC-Universidad de Zaragoza, Facultad de Ciencias, Pza S. Francisco s/n, 50009 Zaragoza, Spain,

and

b European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble Cedex 9, France. E-mail: jgr@unizar.es


Abstract:

Here the correlation between the chemical shift in X-ray absorption spectroscopy, the geometrical structure and the formal valence state of the Mn atom in mixed-valence manganites are discussed. It is shown that this empirical correlation can be reliably used to determine the formal valence of Mn, using either X-ray absorption spectroscopy or resonant X-ray scattering techniques. The difficulties in obtaining a reliable comparison between experimental XANES spectra and theoretical simulations on an absolute energy scale are revealed. It is concluded that the contributions from the electronic occupation and the local structure to the XANES spectra cannot be separated either experimentally or theoretically. In this way the geometrical and electronic structure of the Mn atom in mixed-valence manganites cannot be described as a bimodal distribution of the formal integer Mn3+ and Mn4+ valence states corresponding to the undoped references.


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