The relationship between the electronic structure and thermoelectric properties of Zintl compounds M2Zn5As4 (M = K, Rb)

Abstract

The electronic structure and the thermoelectric properties of M₂Zn₅As₄ (M = K, Rb) are studied by the first principles and the semiclassical BoltzTraP theory. It is determined that they are semiconductors with an indirect band gap of about 1 eV, which is much larger than that of Ca₅Al₂Sb₆ (0.50 eV). The calculated electronic localization function indicates that they are typical Zintl bonding compounds. The combination of heavy and light bands near the valence band maximum may improve their thermoelectric performance. Rb₂Zn₅As₄ exhibits relatively large Seebeck coefficients, high electrical conductivities, and the large “maximum” thermoelectric figures of merit (Z_eT). Compared with Ca₅Al₂Sb₆, the highest Z_eT of Rb₂Zn₅As₄ appears at relatively low carrier concentration. For Rb₂Zn₄As₅, the p-type doping may achieve a higher thermoelectric performance than n-type doping. The thermoelectric properties of Rb₂Zn₅As₄ are possibly superior to those of Ca₅Al₂Sb₆.