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

Abstract

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.

First-Principles Thermoelectric Study of SrMgSi and CaMgGe Zintl-Phase Compounds

“…This suggests a weaker interaction of the anionic network with cations sitting in large channels for CaMgGe compared to SrMgSi, which is consistent with the bond environment analysis of the crystal structures in Figure . A small k min / k max ratio intuitively implies weak bonding in the structure, which would reduce the average stiffness of the lattice, lower the sound velocity, and thus decrease the lattice thermal conductivity. , …”

“…A small k min /k max ratio intuitively implies weak bonding in the structure, which would reduce the average stiffness of the lattice, lower the sound velocity, and thus decrease the lattice thermal conductivity. 53,55 We further investigate the phonon transport properties in SrMgSi and CaMgGe compounds. Figure 5a−c shows the calculated phonon group velocity, lifetime, and Gruneisen parameter (γ) for the two compounds at room temperature.…”

Improved Thermoelectric Performance of NbCoSb with Intrinsic Nb Vacancies and Ni-Doping-Induced Band Degeneracy

“…The latter can be achieved by defect engineering to strengthen the phonon scattering . Band degeneracy ( N v ), consisting of both symmetry and orbital degeneracies, is based on the effective total number of independent carrier pockets or valleys in the Brillouin zone (BZ) . So far, multiple-band degeneracy has been widely acknowledged to be beneficial for high TE performance.…”