Thermoelectric performance of Li doped, p-type Mg2(Ge,Sn) and comparison with Mg2(Si,Sn)

摘要

Solid solutions with chemical formula Mg2(Si,Ge,Sn) are promising thermoelectric materials with very\udgood properties for the n-type material but significantly worse for the p-type. For power generation\udapplications good n- and p-type materials are required and it has been shown recently that Li doping can\udenhance the carrier concentration and improve the thermoelectric properties for p-type Mg2Si1-xSnx. We\udhave investigated the potential of p-type Mg2(Ge,Sn) by optimizing Mg2Ge0.4Sn0.6 using Li as dopant. We\udwere able to achieve high carrier concentrations (1.4 x 10^20 cm-³) and relatively high hole mobilities\udresulting in high power factors of 1.7 x 10^(-3) Wm^(-1) K^(-2) at 700 K, the highest value reported so far for\udthis class of material. Exchanging Ge by Si allows for a systematic comparison of Mg2(Ge,Sn) with\udMg2(Si,Sn) and shows that Si containing samples exhibit a lower power factor but also a lower thermal\udconductivity resulting in comparable thermoelectric figure-of-merit. The data is furthermore analyzed in\udthe framework of a single parabolic band model to gain insight on the effect of composition on band\udstructure.