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Abstract: 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 Yb x La y Fe2.7Co1.3Sb12 (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. [Copyright &y& Elsevier]

Abstract: Ab-initio calculations of the resonant modes and frequencies for a number of possible fillers in p-type RFe3CoSb12 and RFe4Sb12 were carried out. The results indicate that, although the exact values of fillers’ resonant frequencies in p-type skutterudites are somewhat different from those in n-type Co-based skutterudites, the Einstein-like resonant modes of the fillers are similar to those in n-type materials. Experimentally, several pairs of the fillers were selected and double-filled p-type skutterudite compounds RxMy Fe3CoSb12 (R, M = Ba, Ce, Nd, and Yb) were successfully synthesized. The reduction in the lattice thermal conductivity was realized by extending the range of resonant frequencies. As a result, enhanced ZT values above unity were achieved in these double-filled p-type skutterudites. [Copyright &y& Elsevier]