Enhancement of thermoelectric efficiency of CoSb(3)-based skutterudites by double filling with K and Tl

The high-temperature thermoelectric properties of thallium (Tl) and potassium (K) double-filled cobalt antimonide (CoSb(3))-based skutterudites with nominal compositions Tl(x)K(0.3)Co(4)Sb(12) (x = 0.1 − 0.3) were investigated. The filling fraction of Tl in CoSb(3) was enhanced by co-filling with K, which resulted in all of the samples showing the filled-skutterudite single phase. Owing to the high filling ratio, the carrier concentration in the sample with x = 0.3 was as high as 4.3 × 10(20) cm(−3) at room temperature. Furthermore, quite low lattice thermal conductivity (as low as 0.9 Wm(−1)K(−1)) was obtained for the sample with x = 0.3, probably because of strong phonon scattering by the Tl and K co-rattling effect, which resulted in a maximum zT of around one at 773 K.