Research of the impact of uniaxial tension on the thermoelectric properties of NbCoX (X=Ge, Sn, Pb) compounds

Half-Heusler materials have been confirmed as excellent thermoelectric materials. To simulate the stress conditions in engineering applications, we adopt uniaxial tensile strain to assess the impact of lattice changes on NbCoX (X=Ge, =Ge, Sn, Pb) compound's thermoelectric performance. The research reveals that when NbCoX compounds are stretched by 1.5 %, the material almost does not decrease the power factor but significantly reduces thermal conductivity, thereby enhancing the ZT value. At a carrier concentration of 1E22 cm(-3) and a temperature of 873 K, the predicted ZT values for p-type NbCoSn compound reach 0.359 and 0.354 after stretching by 1.5 % in the x-y and z directions, respectively. Compared to the previous original values, this improvement is approximately 1.5 times, highlighting the significant role of tensile strain in enhancing thermoelectric performance. This may be attributed to changes in compound lattice symmetry induced by strain, leading to increased defects and interfaces, which complicate phonon transport paths, resulting in a decrease in the average phonon mean free path and consequently lowering thermal conductivity. Additionally, with the increase in atomic number of Ge, Sn, and Pb, their thermoelectric figure of merit also increases continuously, with ZT values remaining higher under stretching than compression. Such research provides a new avenue for designing and optimizing high-performance thermoelectric materials and offers insights into strain engineering for future exploration of thermoelectric materials.