Ab initio investigation of Co–Ta–Sn Heusler alloys for thermoelectric applications

Abstract

Heusler alloys have shown to be promising materials for thermoelectric applications. This work presents a theoretical study of Heusler alloys within the GGA-PBE and hybrid (HSE06) approaches. The cubic (C1b) CoTaSn half-heusler compound exhibits semiconductor characteristics and a bandgap of 1.18 eV, when Co occupies the Wyckoff 4c site. On the other hand, the cubic (L21) Co2TaSn full-heusler is a half-metal with a bandgap of 1.36 eV in the spin up channel, when Co in the Wyckoff 4c/8c sites. For both systems, the total magnetic moment agrees with the prediction given by Slater-Pauling rule. The analysis from the Bader charge and ELF functions indicates a formation of covalent-polar bonds in the studied alloys. Also, effective masses were obtained, highlighting this as an important feature for high performance thermoelectrics. From Wannier functions, the thermoelectric parameters were calculated for the CoTaSn alloy and the results compared with the experimental data available in literature.