LAUSR

Abstract The maximum dimensionless figures of merit were 0.57 at 590 K and 0.82 at 640 K for the K 9 Ba 15 Al 38 Sn 98 and K 9 Ba 15 Al 31 Ga 8 Sn 97 sintered samples, respectively, which were lower than that 1.17 of K 6 Ba 18 Ga 40 Sn 96 . 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 cm 2  V −1  s −1 , which were lower than that ∼170 cm 2 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.