Thermoelectric Properties of the As/P-Based Zintl Compounds EuIn <sub>2</sub> As <sub> 2– <i>x</i> </sub> P <sub> <i>x</i> </sub> ( <i>x</i> = 0–2) and SrSn <sub>2</sub> As <sub>2</sub>
Keisuke Shinozaki, Yosuke Goto, Kazuhisa Hoshi, Ryosuke Kiyama, Naoto Nakamura, Akira Miura, Chikako Moriyoshi, Yoshihiro Kuroiwa, Hidetomo Usui, Yoshikazu Mizuguchi
Abstract
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 = 0–2) and SrSn2As2, and examined their potential for use as thermoelectric materials. These compounds show p-type polarity with Hall carrier concentrations of ∼1019 cm–3 for EuIn2As2–xPx and ∼1021 cm–3 for SrSn2As2 at 300 K. The high carrier concentration of SrSn2As2 is likely due to self-doping by hole-donating Sn vacancies. The electrical power factor reaches ∼1 mW m–1 K–2 at ∼600 K for EuIn2As2–xPx with x = 0.1 and 0.2, which is almost twice that of the end-member compounds (x = 0 and 2). The lattice thermal conductivity κl is determined to be 1.6–2.0 W m–1 K–1 for EuIn2As2 and SrSn2As2 and 2.8 W m–1 K–1 for EuIn2P2 at 673 K. The dimensionless figure of merit reaches ZT = 0.29 at 773 K for EuIn2As2–xPx with x = 0.2, owing to the optimized carrier concentration and/or electronic structure, as well as reduced lattice thermal conductivity in the solid solution. First-principles calculations show that EuIn2As2 and SrSn2As2 are topologically nontrivial materials with band inversion, while EuIn2P2 is a conventional semiconductor with a band gap. The present study demonstrates that As/P-based Zintl compounds can also show promising thermoelectric properties, thus expanding the frontier for efficient thermoelectric materials.