Structural defects in compounds ZnXSb (X=Cr, Mn, Fe) : Origin of disorder and its relationship with electronic properties

Abstract

Crystallographic disorder is known to be crucial for the understanding of transport properties of intermetallic compounds. ZrSiS-type phases with the general formula ZnXSb, where X is a transition metal, are recognized for their extraordinarily large amount of structural defects. Here, we explain the origin of the disorder and investigate its influence on the electronic behavior of ZnCrSb, ZnMnSb, and ZnFeSb. Synchrotron diffraction data revealed substantial amounts of vacancies on the transition-metal sites for all three compounds. Based on bonding analysis and calculations of crystal orbital Hamilton population (COHP), we claim that the defects originate from antibonding interactions on a two-dimensional square sublattice formed by X atoms. To test our thesis, we compare the ZrSiS-type materials with the chemically similar phase, ZnNiSb, which crystallizes in the MgAgAs-type cell. In this structure, the closest X-X distance is almost doubled with respect to the ZrSiS-type counterparts. In concert with expectations, the COHP calculation for ZnNiSb does not show an X-X antibonding interaction, and virtually no defects are detectable via the experimental diffraction analysis. From the perspective of electron transport, ZrSiS-type compounds were characterized by a residual resistivity ratio (RRR) that was significantly lower than that of ZnNiSb, which indicates stronger point-defect scattering of electrons in our disordered compounds. At the lowest temperatures, we also observed, for ZrSiS-type compounds, signatures of another phenomenon known exclusively for disordered metallic conductors: the Altshuler-Aronov (AA) correction to Coulomb interaction. The effect is not present for the defect-free compound ZnNiSb. ZnFeSb shows the lowest RRR and the highest onset temperature of the AA effect. Furthermore, heat-capacity studies revealed order of magnitude enhancement of Sommerfeld coefficient for ZnFeSb with respect to the value obtained from ab initio density of states calculations. This finding might be correlated to the structural instability. The presented analysis can be useful for understanding materials in which structural disorder significantly affects the electronic properties.