Thermoelectric and transport properties of sintered type-II clathrate Cs8Ba16Ga40Sn96

Abstract

Cs8Ba16Ga40Sn96 was expected to have good thermoelectric properties; we prepared almost single-phase sintered samples of the clathrate. They exhibited a maximum dimensionless figure-of-merit, 0.87, room-temperature (RT) mobility, ~50 cm2 V−1 s−1, and RT lattice thermal conductivity, 12 mW cm−1 K−1. However, these values were inferior to those, 1.19, 170 cm2 V−1 s−1, and 5 mW cm−1 K−1, of (K, Ba)24(Ga, Sn)136, respectively. Band structure calculation suggests that Cs8Ba16(Ga, Sn)136 would have high carrier mobility like (K, Ba)24(Ga, Sn)136. However, the former sintered samples strongly suffered from potential barrier scattering and impurity band conduction; the impurity band conduction may be associated with localized states due to Sn vacancies. Also, the clathrate had relatively large atomic displacement parameters (ADP) of ~0.1 A2, but the rattling effect to suppress thermal conduction was not so strong because the ADP were in on center mode.