Enhanced thermoelectric performance of P-type CaMg2Bi1.98 and optimized CaAl2Si2-type Zintl phase module with equal cross-section area

Abstract

Recently, Zintl phase Mg3Sb2 has displayed superior n-type thermoelectric properties. However, the corresponding p-type thermoelectric materials with high thermoelectric properties are still in urgent need. CaMg2Bi2-based Zintl compound attracts increasing enthusiasm in recent years due to its high carrier mobility and low lattice thermal conductivity. Here, Yb is used to replace Ca to further tune thermoelectric transport behavior of CaMg1.9Zn0.1Bi1.98, an optimized composition according to previous work. The synergistic effect of the enhanced carrier concentration caused by electronegativity difference in cation site and the suppressed lattice thermal conductivity induced by the stronger point defects scattering leads to the peak ZT of 1.0 in Ca0.65Yb0.35Mg1.9Zn0.1Bi1.98, which exceeds most of reported CaMg2Bi2-based materials. The maximum ZTeng of single p-type leg Ca0.65Yb0.35Mg1.9Zn0.1Bi1.98 is up to 0.54 between Tc = 300 K and Th = 773 K, catching up with the current highest level in 1-2-2 Bi-based materials. Moreover, the interrelationship between conversion efficiency and p-n pair cross-section area ratio (An/Ap) is considered. For n-type Mg3.1Co0.1Sb1.5Bi0.49Te0.01/p-type Ca0.65Yb0.35Mg1.9Zn0.1Bi1.98 pair, a maximum conversion efficiency of ~12% is obtained at the optimum An/Ap approaching to 1. This prominent conversion efficiency and equal cross-section area facilitate the module fabrication process and exhibit bright prospect of CaMg2Bi2-based thermoelectric materials.