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

• We model Fe K-edge XANES for FeSexTe1−x using a model of local phase separation.
• Our model includes magnetic order, compositional disorder and two FeSe(Te) lenghts.
• We reproduce the increase of spectral weight in the pre-edge with Se concentration.
• Calculated density of states correlates with the drop on Tc at high Te content.

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(εF), for high Te content is consistent with the suppression of superconductivity in the title system.