Thermoelectric properties of RbZn₄As₃

Zintl phase compounds are one of the most famous systems of thermoelectric materials. In particular, Sb-based 122-Zintl compounds have been intensively explored, resulting in finding many new thermoelectric materials that the dimensionless figure-of-merit (ZT) exceeds the value of 1. On the other hand, we have found high performance thermoelectric materials in As-based Zintl compounds ^[1-3]. Although lighter atomic mass of As than Sb is a disadvantage in terms of the lattice thermal conductivity, those exhibit low thermal conductivity. Recently, we have found that As-based 143-Zintl compounds of NaZn₄As₃ exhibit extremely low lattice thermal conductivity ^[4]. Because it consists of double conduction layers, higher carrier mobility than 122 compounds could be expected.

In this study, we synthesized RbZn_4-xCu_xAs₃ by solid-state reaction. We found that it exhibits extremely low lattice thermal conductivity of 0.77 W/mK at T = 797 K resulting in high ZT value of 0.53 for x = 0.02 sample. Neutron powder diffraction measurements were conducted to determine atomic parameters of crystal structure including the atomic displacement parameters. The origin of low thermal conductivity will be discussed based on the results.