Electronic properties, stability and thermoelectric response of CoFeZrZ (Z= Ge, Sb) quaternary Heuslers

Abstract

A set of ab-initio calculations have been performed to investigate the structural, electronic and thermoelectric properties, in addition to mechanical stability of CoFeZrZ (Z = Ge, Sb) quaternary alloys. Both Co based systems were found to be true half-metals with indirect band gaps. These last ones sustain a wide range of lattice compression, which enables the minimization of defects during the formation of multilayers. Moreover, the elastic properties have shown that CoFeZrZ systems are mechanically stable and ductile in nature. They also possess small anisotropy values, thus lowering the probability of developing micro-cracks during their growth. When measuring the melting temperature, both alloys were found to exhibit a high Tmelt, which confirms their atomic bonding strength. From the calculated phonon dispersion curves, CoFeZrGe have proven to be dynamically stable. However, for CoFeZrSb, the phonon band structure has shown a dynamical instability of this alloy. Finally, we have estimated the thermal transport properties dependence on chemical potential and temperature. The calculated figure of merit (ZT) was 0.29 for CoFeZrGe at 500 K and 0.31 for CoFeZrSb at 700 k. We have also measured the power factor, where the maximum values have reached as high as 11.68*1011 (10.18*1011) W·K−2m−1s−1 for CoFeZrGe (CoFeZrSb) alloy, which favors a further study of these potential thermoelectric materials.