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 the Zintl arsenide Eu5In2As6. The electrical resistivity at 300 K with n-type polarity was decreased to 7.6 x 10^-1 ohmcm 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 x 10^-3 ohmcm with a carrier concentration of 2.8 x 10^20 /cm3 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/mK 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 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.