The nanoscale structure and unoccupied valence electronic states in FeSe1−xTex chalcogenides probed by X-ray absorption measurements

Abstract

We have studied the nanoscale structure and unoccupied electronic states in FeSe_1−xTe_x by a combined analysis of Se K, Te L₁ and Fe K-edges X-ray absorption measurements. Extended X-ray absorption fine structure (EXAFS) results show that iron–chalcogen (Fe–Se and Fe–Te) distances in ternary FeSe_1−xTe_x are similar to those measured for binary FeSe and FeTe. The local Fe–Se/Te distances determined by different absorption edges fit well in the characteristic Z-plot of random alloys, providing unambiguous support to the inhomogeneous nanoscale structure of the ternary FeSe_1−xTe_x system. X-ray absorption near-edge structure (XANES) spectra reveal a gradual evolution of the unoccupied valence electronic states as a function of Te-substitution in FeSe_1−xTe_x. The Fe 3d–Se 4p/Te 5p hybridization is found to decrease with Te-substitution, accompanied by an increase in unoccupied Se 4p states and a decrease in unoccupied Te 5p states. The results are discussed in the frame of local inhomogeneity in the FeSe_1−xTe_x system driven by random alloying of Se/Te atoms.