Theoretical investigation of structural, electronic and thermoelectric properties of $$p{-}n$$ type $$\hbox {Mg}_{2}\hbox {Si}_{1-x}\hbox {Sn}_{x}$$ system

Abstract

Based on the density functional theory and the Boltzmann transport theory, the thermoelectric properties of $$\hbox {Mg}_{2}\hbox {Si}_{1-x}\hbox {Sn}_{x}$$ solid solution with $$x= 0.25, 0.5 \hbox { and } 075$$ were investigated. The calculated structural parameters were in good agreement with the previous work and the mechanical and dynamical stabilities were confirmed. The electronic band structure computed using the Tran-Blaha-modified Becke and Johnson (TB-mBJ) exchange potential indicated that the band gap can be tuned by the alloy effect. We combined first-principles calculations and the semiclassical Boltzmann transport theory by considering the electronic transport in the $$\hbox {Mg}_{2}\hbox {Si}_{1-x}\hbox {Sn}_{x}$$ solid solution to determine the effect of varying the Sn composition on the thermoelectric performance. Our results have shown exceptionally high electrical conductivity for $${\hbox {Mg}}_{2}\hbox {Sn}$$ and higher Seebeck coefficient for $$\hbox {Mg}_{2}\hbox {Si}$$ . The highest figure of merit (ZT) was predicted for $$\hbox {Mg}_{2}\hbox {Si}_{1-x}\hbox {Sn}_{x}$$ solid solution with $$x = 0.5$$ where ZT has reached 0.55 with carrier concentration charge $$n = 10^{20}\hbox { cm}^{-3}$$ (p-type doping) at intermediate temperatures. Consequently, the alloying system with p-type doping may improve the thermoelectric properties compared to the $$\hbox {Mg}_{2}\hbox {Si}$$ and $$\hbox {Mg}_{2}\hbox {Sn}$$ pristine compounds.