Half-metallic behavior, thermodynamic stability and thermoelectric performance of new CoXMnSi (X=Rh, Tc) quaternary Heuslers

Half-metallic, thermoelectric, and also thermodynamic stability of CoXMnSi (X = Rh, Tc) quaternary Heusler compounds were performed by density functional theory calculations. These compounds have an equilibrium volume with the lattice constants of 5.81 and 5.77 Aᵒ for CoRhMnSi and CoTcMnSi, respectively, which is consistent with the other functions. Moreover, the bulk moduli of these compounds have been calculated to be 225.8GPa and 242.5GPa, respectively, which indicates their very high crystalline hardness. Thermodynamic phase diagrams confirmed the thermodynamic stability of these compounds. Electronic calculations show half-metallic behavior with 100% spin polarization at the Fermi level for both compounds. The CoRhMnSi has 0.65eV and 0.72eV, and CoTcMnSi has 0.22eV and 0.51eV spin gap in minority spin when applying the GGA and GGA+U approximations, respectively. Also, the study of thermoelectric properties shows that these compounds with a figure of merit index of 0.99 at room temperature are suitable candidates for thermoelectric purposes, which is in agreement with other works.