Enhanced Thermoelectric Performance in SmMg2Bi2 via Ca-Alloying and Ge-Doping

Abstract

Zintl phase compounds with a CaAl2Si2 structure are promising thermoelectric materials. In this paper, enhanced thermoelectric performance was achieved in SmMg2Bi2, a new member of AB2X2 compounds, via Ca-alloying and Ge-doping. The introduction of point defects by alloying Ca on the Sm site significantly reduces the lattice thermal conductivity, and the lowest value was achieved when the Sm/Ca molar ratio is 1:1. Doping Ge on the Bi site increases the hole concentration of the material, which successfully suppresses the bipolar effect and significantly improves the power factor (PF) in the whole temperature range. Due to the decrease of thermal conductivity and the increase of PF over 323–873 K, the peak zT value of Sm0.5Ca0.5Mg2.15Bi1.99Ge0.01 reached 0.71 at 873 K and the zTave approached 0.44, about 51 and 47% enhancement compared with the pristine sample, respectively. This work provides a thermoelectric performance optimization strategy that can be used for other AB2X2 compounds.