First-principles study of thermoelectric properties of Mg₂Si-Mg₂Pb semiconductor materials

Mg₂X^IV (X^IV = Si, Ge, Sn) compounds are semiconductors and their solid solutions are believed to be promising mid-temperature thermoelectric materials. By contrast, Mg₂Pb is a metal and few studies have been conducted to investigate the thermoelectric properties of Mg₂Si-Mg₂Pb solid solutions. Here, we present a theoretical study exploring whether Mg₂Pb-Mg₂Si solid solutions can be used as thermoelectric materials or not. We firstly constructed several Mg₂Si_1-xPb_x (0 ≤ x ≤ 1) structures and calculated their electronic structures. It is suggested that Mg₂Si_1-xPb_x are potential thermoelectric semiconductors in the range of 0 ≤ x ≤ 0.25. We then explicitly computed the electron relaxation time and both the electronic and lattice thermal conductivities of Mg₂Si_1-xPb_x (0 ≤ x ≤ 0.25) and studied the effect of Pb concentration on the Seebeck coefficient, electrical conductivity, thermal conductivity, and thermoelectric figure of merit (ZT). At low Pb concentration (x = 1/16), the ZT of the Mg₂Si_1-xPb_x solid solutions (up to 0.67 at 900 K) reaches a maximum and is much higher than that of Mg₂Si.