A Theoretical Study on the Thermal Conductivity and Thermoelectric Properties of CoNbSi and CoNbSn

We utilized density functional theory to systematically investigate the thermoelectric performance of two low-cost, environmentally friendly half-Heusler materials: CoNbSi and CoNbSn. It is interesting that relatively light CoNbSi exhibits a lower lattice thermal conductivity (4.89 W/(m K) @1000 K) than CoNbSn by solving the phonon Boltzmann transport equation, which is mainly due to strong anharmonicity and a large phonon scattering rate. From the calculated electronic structure, we find that band degeneracy near the valence band maximum can reach 12. Such large valence band degeneracy will lead to good electrical transport properties of p-type materials. Owing to the relatively low lattice thermal conductivity and the good electrical transport properties, the highest ZT value can reach 2.1 and 1.6 at 1000 K for p-type and n-type CoNbSi, respectively, which implies that CoNbSi is a promising low-cost half-Heusler thermoelectric material. Our work not only provides a promising candidate for future experimental investigation but also provides a useful guide to seek and design new thermoelectric materials with strong anharmonicity and high band degeneracy.