Thermoelectric properties of Rb(Cd,Zn)₄As₃

Zintl phase compound is one of the most promising thermoelectric materials. In particular, various high-performance thermoelectric materials were found in 122-Zintl phase compounds AM₂X₂ (A: alkali metal, alkaline-earth metal, M: transition metal, X: pnictogen). Recently, we found that 143-Zintl phase compounds of RbZn₄As₃, whose crystal structure is close to 122-Zintl phase compounds, exhibits relatively high thermoelectric performance with the value of the dimensionless figure-of-merit (ZT) to be 0.53 (T=797K) [1]. We proposed that 143-Zintl phase compound can be a new class of high-performance thermoelectric materials.

In this study, we extended the study to Rb(Cd,Zn)₄As₃, where Zn was replaced by Cd to reduce the lattice thermal conductivity. We synthesized those samples by solid-state reactions. The total thermal conductivity of RbCd₄As was extremely low to be 0.83 W/mK (T=470 K) that is advantageous for achieving high ZT value. Crystal structure analysis was conducted by powder neutron diffraction measurement. The results show that Rb atoms vibrate relatively large, which can be the origin of its low lattice thermal conductivity.