Compositional dependence of the thermoelectric properties of (Sr_xBa_xYb_{1 − 2x})_yCo₄Sb₁₂skutterudites

Abstract

High temperature thermoelectric (TE) properties for triple-filled skutterudites (Sr(x)Ba(x)Yb₁₋₂x)(y)Co₄Sb₁₂ were investigated for alloy compositions in two sections of the system: (a) for x = 0.25 with a filling fraction y ranging from 0.1 to 0.25 and (b) for 0 < x < 0.5 and y = 0.11 + 0.259x. The representation of the figure of merit, ZT, as a function of skutterudite composition, defined the compositional range (0.25 < x < 0.4; 0.18 < y < 0.24) with ZT over 1.4 at 800 K. It was shown that an enhanced TE performance for these triple-filled skutterudites is caused by low electrical resistivities and low lattice thermal conductivities, as well as by a fine tuning of the chemical composition. Low temperature measurements for the samples with the highest ZT values showed that even a small change of the filler ratios changes the contribution of scattering effects, the carrier concentration and the mobility.

Nanostructuring of p- and n-type skutterudites reaching figures of merit of approximately 1.3 and 1.6, respectively

“…Previous calculations to determine the number of charge carrier densities from Eq. (3) compared well with data extracted from measured Hall coefficients [48,53,116]. Due to practically identical gradients of all six Seebecktemperature curves, the charge carrier density for DD y (Fe 1Àx Co x ) 4 Sb 12 skutterudites was estimated to be $4.5 ± 0.4 Â 10 20 cm À3 (300-500 K).…”

In-doped multifilled n-type skutterudites with ZT= 1.8

“…3a shows the dependence of the filling level on the lattice parameter of (Sr, Ba, Yb) y Co 4 Sb 12 skutterudites with a linear fit taken from previous works of the authors [70,71,78]. Data of the indium quadruple-filled skutterudites (red filled circles) fit well to those of the triple filled alloys.…”

“…Ad a) The (Sr 0.33 Ba 0.33 Yb 0.33 ) 0.35 Co 4 Sb 12.3 samples were prepared from Sr, Ba (99 + mass%, Sigma-Aldrich, Germany), Yb (99.9 mass%, Rhône-Poulenc, Shelton, CT, USA) and Sb ingots (99.8 mass% metals basis, Alfa Aesar, Germany), Co-powder (99.9 mass%, particle size < 150 lm, Sigma-Aldrich, Germany) and Co pieces (99.9 mass%, Alfa Aesar, Germany) as described in detail earlier [70,71]. The bulk was (i) ball milled in tungsten carbide vessels (volume = 80 ml, Ar filled) in a Fritsch planetary mill (Pulverisette 4) with 25 balls of a diameter of 10 mm for 2 h at 200 rpm (main disk) and À500 rpm (vessels) followed by (ii) hot pressing (HP) under argon in a FCT uniaxial hot-press system HP W 200/250 2200-200-KS with the following press conditions: 700°C and 56 MPa (2 h).…”

“…The structural and physical properties of these In-filled skutterudites were compared with each other and with a reference sample without In, prepared under the same conditions in a previous investigation [70]. Particular attention is paid to the dependence of the total filling level as well as the In-content on the added wt.% of In 0.4 Co 4 Sb 12 and the grain and crystallite size.…”

Novel K rattling: A new route to thermoelectric materials?

“…16 Even further reductions have been reported in multi-filled compounds where two or more elements are used as rattler atoms. 7,[17][18][19][20][21][22][23][24] The larger reductions in the thermal conductivity in the thermal conductivity of multi-compared to single-filled materials is attributed to the scattering of a broader range of host lattice phonon frequencies due to the rattlers of the different elements vibrating at different frequencies. In a recent contribution 25 on the study of rattling in the Al-doped β-pyrochlores, AAl0.33W1.67O6 (A = K, Rb, Cs), we reported the discovery of novel rattling of K atoms in KAl0.33W1.67O6 involving both vibrations at a broad range of frequencies as well as local diffusion.…”