The Influence of Si Addition on Li Doped Mg₂(Ge, Sn) Thermoelectric Properties

Mg₂(Ge, Sn) solid solutions are one of eco-friendly thermoelectric materials applied on mid-temperature (500~800 K). Although dimensionless figure of merit ZT of n type Mg₂(Ge, Sn) has reached 1.4, the maxima ZT of p type Mg₂(Ge, Sn) is just 0.5 so far. In this paper, Si were added to p type Mg_1.92Li_0.08Ge_0.4Sn_0.6 samples. The addition of Si results in Si-rich phase, which can create interface barrier to block low-energy carrier and reduce thermal conductivity. The samples of Mg_1.92Li_0.08Ge_0.4Sn_0.6-xSi_x (x=0, 0.025, 0.05, 0.075, 0.1) were fabricated by two-steps solid recreation, ball milling and hot-pressing, and their thermoelectric transport parameters were investigated, with specially analyzing the influence of Si addition on thermal conductivity. The results demonstrate that the Si addition observably improve the power factor, with the simultaneously decreasing of both the lattice thermal conductivity and the electrical thermal conductivity. Finally, the maximum figure of merit ZT of Mg_1.92Li_0.08Ge_0.4Sn_0.525Si_0.075 reaches 0.75 at 723 K.