Thermoelectric properties of Yb-filled CoSb3 skutterudites

Abstract

Yb-filled skutterudites YbzCo4Sb12 (z = 0, 0.1, 0.2, 0.3, 0.4) were prepared by encapsulated melting and hot pressing. The filling effects of Yb on the transport and the thermoelectric properties of the skutterudites were examined. In the case of z ≥ 0.3, a secondary phase (YbSb2) was formed, indicating that the filling fraction limit of Yb was z = 0.2 -0.3. The intrinsic CoSb3 had a high positive Seebeck coefficient, but Yb-filled CoSb3 exhibited a negative Seebeck coefficient. In the case of z ≤ 0.1, the maximum absolute value of the Seebeck coefficient was | −231| μVK −1 , and in the case of z ≥ 0.2, the absolute value of the Seebeck coefficient increased with increasing temperature. The electrical conductivity increased and the Seebeck coefficient decreased with increasing Yb filling content due to the increased carrier concentration. The thermal conductivity was reduced significantly by Yb filling, mainly due to a decrease in the lattice thermal conductivity. Also, the lattice thermal conductivity decreased with increasing Yb filling content, indicating that the phonon scattering was caused by the rattling of Yb fillers in the voids of the skutterudite structure. Yb0.2Co4Sb12 showed the highest figure of merit of 1.0 at 823 K.

Structure, Phase Composition, and Thermoelectric Properties of YbxCo4Sb12 and Their Dependence on Synthesis Method

“…This maximum is typical for samples with only small Yb content indicating the onset of intrinsic conduction. 21,30,53,56 Hall effect data yield a direct relation between charge carrier densities n and the filling fraction x 2a . The results of these measurements are shown in Figure 7.…”

“…Park et al later synthesized skutterudite samples via encapsulated melting followed by an annealing process and deduced a FFL of 0.3 from the appearance of secondary phases in XRD patterns for samples with nominal Yb contents ≥ 0.3. 30 Only recently, Tang et al reported the possibility of synthesizing Yb 0.49 Co 4 Sb 12 with a yet higher filling fraction of x = 0.49 determined by EPMA, using a similar synthesis routine but increasing the annealing temperature to 1073 K. 31 These findings, however, were contested by Wang et al, who employed again a similar routine albeit with lower annealing temperature of 1023 K and who reported a FFL of only ∼0.29 based on energy-dispersive X-ray spectroscopy (EDX). 32 Meanwhile, Yang et al reported on a non-equilibrium synthesis method for Yb x Co 4 Sb 12 that allows to increase the filling fraction even further.…”

Thermoelectric properties of YbxCo4Sb12prepared under high pressure

“…[7][8][9][10][11][12][13] However, this method is not suitable for the smaller (and heavier) rare earths filled skutterudite compounds. 14) It has been demonstrated that the compounds (smaller or heavier rare earths filled skutterudites), which can not be synthesized under ambient pressure, might be synthesized with the aid of high pressure.…”

Enhancement of Thermoelectric Properties of Yb0.25Co4Sb12 Skutterudites through Ni Substitution

“…The result found that, the main phase of skutterudite CoSb 3 (PDF 03-065-1791) structure (space group Im-3) was observed, with minor amount of secondary phases such as; CoSb 2 (PDF 03-065-4102) and Ni (PDF 00-001-1258) have been detected in all doped samples. However, Yb 0.25 Co 4 Sb 12 bulk sample shows only a single phase of skutterudite structure mainly due to the limited of Yb-filler in the void (0.2 ≤ x ≤ 0.3) according to Park et al (2014). Moreover, the Rietveld refinement analysis of XRD pattern implemented for all bulk samples, the structure showed in Figure 2.…”