Unusual consequences of donor and acceptor doping on the thermoelectric properties of the MgAg0.97Sb0.99 alloy

Abstract

MgAgSb alloys have been demonstrated to be one of the two best classes of low-temperature thermoelectric materials. In this study, a series of dopants to the slightly Ag- and Sb-deficient MgAg_0.97Sb_0.99 alloy are studied to explore their consequences on the power factor (PF) and thermoelectric figure-of-merit (ZT) of the alloy. The systematic study reveals that starting from the MgAg_0.97Sb_0.99 alloy, the donor dopant degrades both the PF and ZT, whereas the acceptor dopant enhances the PF without affecting the ZT. Both the donor and acceptor make the total thermal conductivity higher. A full-scale thermoelectric computation based on first-principles calculations and the Boltzmann transport theory is carried out to validate the experimental results. The calculated results for the donors and acceptors are semi-quantitatively consistent with our experimental results. The present study suggests that carrier doping alone may not be sufficient to significantly improve the overall thermoelectric performance of the MgAg_0.97Sb_0.99 alloy.