Thermoelectric properties of sintered type-II clathrates (K, Ba)24(Ga, Sn)136 with various carrier concentrations

We reported the thermoelectric properties of the sintered typc-II clathratc K8Ba16Ga40Sn96 in a previous paper [S. Koda et al., J. Appl. Phys. 116, 023710 (2014)1. The clathrate had a high dimensionless figure of merit ZT, namely, 0.93. In this study, we optimized the carrier concentration n by modifying the chemical compositions of (K, Ba)(24)(Ga, Sn)(136) samples, and heat treated the sintered samples. The carrier mobilities mu were improved because of the reduction in potential barrier scattering at grain boundaries. The room-temperature (RT) n values varied from 7.7 x 10(17) to 3.7 x 10(19) cm(-3); the maximum RT mu value was 170 cm(2)V(-1)s(-1), Consequently, we obtained a high ZT value of 1.19 at 630K for a 2.5 x 1019cm(-1);. This material therefore has good thermoelectric properties. (C) 2015 AIP Publishing LLC.