Improved Thermoelectric Properties of N-Type MgSb through Cation-Site Doping with Gd or Ho.

The success of n-type doping has attracted strong research interest for exploring effective n-type dopants for MgSb thermoelectrics. Herein, we experimentally study Gd and Ho as n-type dopants for MgSb thermoelectrics. The synthesis, structural characterization, and thermoelectric properties of Gd-doped, Ho-doped, (Gd, Te)-codoped, and (Ho, Te)-codoped MgSb samples are reported. It is found that Gd and Ho are effective n-type cation-site dopants showing a higher doping efficiency as well as a superior carrier concentration in comparison with anion-site doping with Te, consistent with the previous theoretical prediction. For n-type MgSb samples doped with Gd or Ho, optimal thermoelectric figure of merit values of ∼1.26 and ∼0.94 at 725 K are obtained, respectively, in MgGdSb and MgHoSb, which are superior to many reported Te-doped MgSb without alloying with MgBi. By codoping with Gd (or Ho) and Te, reduced thermal conductivity and enhanced power factor values are achieved at high temperatures, which results in enhanced peak values well above unity at 725 K. This work reveals Gd and Ho as effective n-type dopants for MgSb thermoelectric materials.