Effect of local atomic phase separation in the x-ray absorption near edge structure spectroscopy of FeSexTe1-x

Ab initio X-ray absorption near edge structure (XANES) calculations for FeSexTe1-x, using a structural model that combines FeSe and FeTe phases at the nanoscale, are compared with Fe K-edge XANES measurements in the "pre-edge" region. The important aspects of this model are (i) magnetic order in the FeTe phase; (ii) Se and Te atoms placed randomly in both FeSe and FeTe crystallographic positions and; (iii) the two distinct distances for Fe-Se and Fe-Te of the bulk phases. The calculated spectra reproduce the observed increase of spectral weight in the experiments on FeSexTe1-x with Se concentration. This is consistent with an inhomogeneous local electronic structure of FeSexTe1-x. Additionally, we have calculated projected electronic density of d-states for the Fe atom, revealing increased spectral weight in the "pre-edge" region of the XANES spectra, which correlates with the increase in Se concentration. The decrease of calculated Fe d-density of states for the Fermi level, N(epsilon(F)), for high Te content is consistent with the suppression of superconductivity in the title system. (C) 2014 Elsevier Ltd. All rights reserved.