Rational composition engineering toward high thermoelectric performance in p-type EuMg2Sb2-based materials

Mg-based compounds are emerging materials for efficient thermoelectric conversion, as exemplified by n-type Mg 3 Sb 2 -based materials, while a high performing p-type Mg 3 Sb 2 material is lacking. EuMg 2 Sb 2 , a derivative of Mg 3 Sb 2 , has revealed potential as a high-performance alternative to p-type Mg 3 Sb 2 -based materials, while pristine EuMg 2 Sb 2 suffers from low carrier concentration. Herein, we reveal that both Zn substitution for Mg and Yb substitution for Eu not only boost the carrier concentration and mobility of p-type EuMg 2 Sb 2 -based materials, but also sharply diminish the lattice thermal conductivity via enhancing phonon scattering. Band structure calculation shows that Zn substitution minimizes the energy difference between different bands at the valence band maximum and reduces the band effective mass, leading to optimized band structure. Combined with the role of Ag doping in increasing the carrier concentration and power factor, p-type Eu 0.5 Yb 0.5 Mg 1.0975 Zn 0.9975 Ag 0.005 Sb 2 sample obtains a maximal dimensionless figure of merit ( zT ) value of 1.18 at 823 K, which compares favorably to those of EuMg 2 Sb 2 and other p-type Mg–Sb-based Zintl materials. This study demonstrates the efficacy and importance of delicate composition engineering in boosting the thermoelectric performance of p-type EuMg 2 Sb 2 .