Thermoelectric properties of p-type YbxLayFe2.7Co1.3Sb12 double-filled skutterudites

Filling two or multiple atoms into the cages of a skutterudite crystal is a successful way to enhance the thermoelectric figure of merit in n-type partially filled skutterudites. Here we use La–Yb double filling to improve the thermoelectric performance of p-type skutterudites YbxLayFe2.7Co1.3Sb12 (x + y = 0.85, x = 0, 0.09, 0.17, 0.25, 0.34, 0.42, 0.85). The samples are synthesized by directly melting the raw materials followed by a long time annealing process. X-ray diffraction measurement confirms the skutterudite structure of the samples. By increasing the filling fraction of Yb, the lattice thermal conductivity is gradually depressed and reaches the lowest value of 0.9 W m−1 K−1 at high temperatures. At the same time, the Seebeck coefficient decreases while the electrical conductivity increases. The maximum power factor around 27 μW cm−1 K−2 for samples Yb0.17La0.68Fe2.7Co1.3Sb12 and Yb0.25La0.60Fe2.7Co1.3Sb12 is achieved at 600 K and 700 K, respectively. Sample Yb0.25La0.60Fe2.7Co1.3Sb12 has the maximum thermoelectric figure of merit 0.99 at 700 K, which is among the highest values among p-type filled skutterudites.