Preparation and thermoelectric properties of sintered type-II clathrates (K,Ba)24(Al,Sn)136

The maximum dimensionless figures of merit were 0.57 at 590 K and 0.82 at 640 K for the K9Ba15Al38Sn98 and K9Ba15Al31Ga8Sn97 sintered samples, respectively, which were lower than that 1.17 of K6Ba18Ga40Sn96. The substituting atom for Sn in the framework of this clathrate affected its electronic and electrical properties significantly. Compared to Ga substitution, Al substitution damaged dispersive bands at the conduction-band edge, resulting in a larger inertial mass. This substitution also caused larger defect densities in the sintered samples. As a result, the Al-substituted sintered samples had room-temperature carrier mobilities of only 30–40 cm2 V−1 s−1, which were lower than that ∼170 cm2 V−1 s−1 of the Ga-substituted ones. On the other hand, the substituting atom did not influence the thermal properties very much. The Al-substituted sintered samples had as low lattice thermal conductivities as 5 mW cm−1 K−1 due to a strong rattling effect like the Ga-substituted ones. •Sn-based type-II clathrates are a good thermoelectric material.•Substituting atoms affect electronic and thermoelectric properties strongly.•Lattice thermal conductivities were as low as 4–5 mW/(cm K).