Solubility study of Yb inn-type skutteruditesYbxCo4Sb12

Abstract

The solubility of Yb in Yb x Co 4 Sb 12 was reported to be 0.19 in bulk skutterudites made by melting and slow cooling method. Surprisingly we increased x close to 0.5 by a special sample preparation method: ball mill and hot press. We show that a higher Yb concentration not only increases the power factor due to a higher electron concentration but also reduces the thermal conductivity k because of stronger phonon scattering. In this way, we have achieved a dimensionless thermoelectric figure of merit ZT of about 1.2 at 550°C in Yb 0.35 Co 4 Sb 12 .

High-performance n-type YbxCo4Sb12: from partially filled skutterudites towards composite thermoelectrics

“…Even large deviations in the experimentally determined Yb FFL have been reported with values ranging from 0.2 to 0.7. 12,[15][16][17][18]21 These experimental results all seem to indicate a strong dependence on the synthetic conditions, which most likely relates to the temperature dependence of the FFL or thermodynamically controlled chemical reaction processes. 22 Dilley et al 18 experimentally derived a Yb FFL of 0.22 from the lattice parameters vs nominal composition, when the samples were synthesized via a combination of induction melting and annealing.…”

“…5,12,13,15 Here, ZT is defined as σα 2 T/κ, where α, σ, κ and T are the Seebeck coefficient, electrical conductivity, thermal conductivity and the absolute temperature, respectively. With increasing Yb content, ZT increases gradually, peaks at x = 0.3 and then decreases rapidly.…”

“…Later, Salvador et al 16 observed a filling fraction of 0.25 (electron probe microanalysis results) for the nominal composition Yb 0.4 Co 4 Sb 12 , which was prepared by an induction melting-long-term annealing-sintering technique, although no sample with nominal Yb content 40.4 was prepared. Recently, Ren's Group used high-energy ball milling to prepare a series of bulk Yb x Co 4 Sb 12 and concluded a very high Yb FFL of 0.5 based on X-ray diffraction (XRD) results, 12,15 and He et al 21 extracted an even higher Yb FFL of 0.68 in Yb x Co 4 Sb 12 thin films by the Rietveld refinements of XRD patterns. Special attention should be paid to the fact that the Yb FFLs determined from many of these previous studies lack sufficient evidence to unambiguously conclude that such high FFLs are true, and none of them show combined experimental results for lattice parameters and experimentally derived Yb compositions as assessed by electron probe microanalysis or energy-dispersive X-ray spectroscopy (EDS).…”

“…10 Among these elements, Yb is one of the most effective fillers to lower lattice thermal conductivity (κ L ) due to its heavy atomic mass and small ionic radius, which result in the lowest rattling frequency of~42 cm − 1 in CoSb 3 . 10,11 Despite being studied extensively because of its demonstrably good TE properties (ZT~1.2-1.4), [11][12][13][14][15][16][17] the filling fraction limit (FFL) of Yb has still not been conclusively determined. Various authors have reported substantially different transport properties for a wide range of Yb filling fractions.…”

“…Various authors have reported substantially different transport properties for a wide range of Yb filling fractions. [11][12][13][15][16][17][18] Shi et al 19 first determined the theoretical FFL of Yb in CoSb 3 to be 0.2 using ab initio calculations. This was done by considering the competing effects of secondary phases (mainly YbSb 2 ); later, Mei et al 20 calculated the Yb FFL of 0.3 using a similar density functional theory approach.…”