Xinjie Ma

Mg₃Bi_2−vSb_v (0 ≤ v ≤ 2) is a class of promising thermoelectric materials that have a high thermoelectric performance around room temperatures, whereas their thermoelectric properties under pressures and temperatures are still illusive. In this study, we examined the influence of pressure, temperature, and carrier concentration on the thermoelectric properties of Mg₃Bi_2−vSb_v using first-principle calculations accompanied with Boltzmann transport equations method. There is a decrease in the lattice thermal conductivity of Mg₃Sb₂ (i.e., v = 2) with increasing pressure. For a general Mg₃Bi_2−vSb_v system, power factors are more effectively improved by n-type doping where electrons are the primary carriers over holes in n-type doping, and can be further enhanced by applied pressure. The figure of merit (zT) exhibits a positive correlation with temperature. A high zT value of 1.53 can be achieved by synergistically tuning the temperature, pressure, and carrier concentration in Mg₃Sb₂. This study offers valuable insights into the tailoring and optimization of the thermoelectric properties of Mg₃Bi_2−vSb_v.

As a promising room-temperature thermoelectric material, the elastic properties of Mg₃Bi_2−xSb_x (0 ≤ x ≤ 2), in which the role of van der Waals interactions is still elusive, were herein investigated. We assessed the effects of two typical van der Waals corrections on the elasticity of Mg₃Bi_2−xSb_x nanocomposites using first-principles calculations within the frame of density functional theory. The two van der Waals correction methods, PBE-D3 and vdW-DFq, were examined and compared to PBE functionals without van der Waals correction. Interestingly, our findings reveal that the lattice constant of the system shrinks by approximately 1% when the PBE-D3 interaction is included. This leads to significant changes in certain mechanical properties. We conducted a comprehensive assessment of the elastic performance of Mg₃Bi_2−xSb_x, including Young’s modulus, Poisson’s ratio, bulk modulus, etc., for different concentration of Sb in a 40-atom simulation box. The presence or absence of van der Waals corrections does not change the trend of elasticity with respect to the concentration of Sb; instead, it affects the absolute values. Our investigation not only clarifies the influence of van der Waals correction methods on the elasticity of Mg₃Bi_2−xSb_x, but could also help inform the material design of room-temperature thermoelectric devices, as well as the development of vdW corrections in DFT calculations.