Design of half-heusler thermoelectric compound TiFe0.5Ni0.5Sb with special quasi-random structure using 18-electron rule

Abstract The double half-Heusler compound TiFe0.5Ni0.5Sb with special quasi-random structure (SQS) has been modeled by using 18-electron rule, which can simulate the inevitable atomic occupation disorder between two sublattices. We studied the electronic structure and thermoelectric (TE) properties of this compound based on first-principle calculations and semi-classical Boltzmann transport theory. The calculated band structure indicates that this compound belongs to a nonmagnetic indirect band gap semiconductor with a band gap of 0.45 eV. The lattice thermal conductivity κ l at room temperature is 11.24 WK−1m−1, which was lower than 18.7 WK−1m−1 for the 18-electron TiCoSb, and decreases as the temperature increased. The reason is that the lattice vibration is enhanced while thermal conductivity is suppressed when the temperature rises. The dimensionless figure of merit ZT of p-type TiFe0.5Ni0.5Sb at 1390 K is evaluated to be 0.35, which is higher than 0.1 for its parent compound 17-electron TiFeSb. The theoretical prediction for TiFe0.5Ni0.5Sb can simulate corresponding experimental results because of the use of SQS and will increase the experimental research of other disordered alloys using 18-electron rule toward designing and improving TE performance.