Thermoelectric Properties of the As/P-Based Zintl Compounds EuIn2As2−xPx (X = 0 to 2) and SrSn2As2

Zintl compounds containing Sb have been studied extensively because of their promising thermoelectric properties. In this study, we prepared As/P-based Zintl compounds, EuIn2As2-xPx (x = 0 to 2) and SrSn2As2, and examined their potential for use as thermoelectric materials. These compounds show hole carrier concentrations of ~10^19 /cm3 for EuIn2As2-xPx and ~10^21 /cm3 for SrSn2As2 at 300 K. The high carrier concentration of SrSn2As2 is likely owing to self-doping by hole-donating Sn vacancies. The electrical power factor reaches ~1 mW/mK2 at ~600 K for EuIn2As2-xPx with x = 0.1 and 0.2. The lattice thermal conductivity is determined to be 1.6–2.0 W/mK for EuIn2As2 and SrSn2As2, and 2.8 W/mK for EuIn2P2 at 673 K. The dimensionless figure of merit reaches ZT = 0.29 at 773 K for EuIn2As2-xPx with x = 0.2. First-principles calculations show that EuIn2As2 and SrSn2As2 are topologically nontrivial materials with band inversion, while EuIn2P2 is a conventional semiconductor with a bandgap. The present study demonstrates that As/P-based Zintl compounds can also show promising thermoelectric properties, thus expanding the frontier for efficient thermoelectric materials.