Theoretical study of thermoelectric properties of p-type Mg2 Si1−x Snx solid solutions doped with Ga

Abstract

Mg2 Si-Mg2 Sn solid solutions are a promising class of thermoelectric materials. The thermoelectric properties of p-type Mg2(Si0.3 Sn0.7)1−y Gay solid solutions with the doping levels as y = 0.05 and y = 0.07 are investigated in the temperature range of 300 K–800 K. By using the nearly-free hole approximation and the Fermi-Dirac statistics, the temperature dependences of Fermi level (Ef), Seebeck coefficient (S), and electrical conductivity (σ) are calculated theoretically and compared with related experimental measurements. The thermal conductivity contributions from carriers (namely acceptor holes in this present work, κc), electron-hole pairs (κbp), and phonons (κph) are included by employing Wiedemann-Franz law, Price's theory, and Srivastava's scheme, respectively. A maximum thermoelectric figure of merit (ZT) of 0.355 is theoretically achieved for the Mg2(Si0.3 Sn0.7)0.95 Ga0.05 sample arising from a high Seebeck coefficient of 175.71 μV/K and low total thermal conductivity of 1.82 W m−1 K−1 at 650 K where its experimental ZT value was reported as 0.356 at 620 K.