Bipolar doping and thermoelectric properties of Zintl arsenide Eu5In2As6

Abstract

Zintl compounds exhibit promising thermoelectric properties because of the feasibility of the chemical tuning of their electrical and thermal transport. While most Zintl pnictides are known to show p-type polarity, recent developments in high-performance n-type Mg₃Sb₂-based thermoelectric materials have encouraged further identification of n-type Zintl pnictides. In this study, we demonstrate the bipolar dopability of Zintl arsenide Eu₅In₂As₆. The electrical resistivity at 300 K with n-type polarity was decreased to 7.6 × 10⁻¹ Ω cm using La as an electron dopant. In contrast to the relatively high resistivity of n-type Eu₅In₂As₆, the p-type resistivity at 300 K was decreased to 5.9 × 10⁻³ Ω cm with a carrier concentration of 2.8 × 10²⁰ cm⁻³ using Zn as a hole dopant. This doping asymmetry is discussed in terms of the weighted mobility of electrons and holes. Furthermore, a very low lattice thermal conductivity of 0.7 W m⁻¹ K⁻¹ was observed at 773 K, which is comparable to that of the Sb-containing analogue Eu₅In₂Sb₆. The dimensionless figure of merit ZT = 0.29 at 773 K was obtained for Zn-doped p-type Eu₅In₂As₆. This study shows that bipolar dopable Eu₅In₂As₆ can be a platform to facilitate a better understanding of the doping asymmetry in Zintl pnictides.