Thermal expansion of skutterudites

Abstract

The current paper gives an overview of the newly obtained thermal expansion coefficients of skutterudites as well as those so far available in literature. Thermal expansion was determined for CoSb 3 , Pt 4 Sn 4.4 Sb 7.6 , for As-and Ge-based skutterudites as well as for various high-ZT skutterudites ͑microand nanostructured͒ with didymium ͑DD͒ and mischmetal ͑Mm͒ as filler atoms in frameworks of ͑Fe 1−x Co x ͒ 4 Sb 12 and ͑Fe 1−x Ni x ͒ 4 Sb 12 , and for double and triple-filled skutterudites such as Ca 0.07 Ba 0.23 Co 3.95 Ni 0.05 Sb 12 and Sr 0.025 Ba 0.075 Yb 0.1 Co 4 Sb 12 . For low temperatures, a capacitance dilatometer was used ͑4-300 K͒, whereas for temperatures 300Ͻ T Ͻ 750 K, a dynamic mechanical analyzer was employed. For a set of Ge-, P-, and Sb-based skutterudites, lattice parameters of single crystals, measured at three different temperatures, were used to derive the thermal expansion coefficient. The semiclassical model of Mukherjee ͓Phys. Rev. Lett. 76, 1876 ͑1996͔͒ has been successfully used to quantitatively describe the thermal expansion coefficient in terms of Einstein and Debye temperatures, which compare well with the corresponding results from specific heat, electrical resistivity, or temperature dependent x-ray measurements.

Multifilled nanocrystalline p-type didymium – Skutterudites with ZT>1.2

“…20a and b) with a ¼ 11.85 Â 10 À6 K À1 and a ¼ 11.86 Â 10 À6 K À1 respectively can be considered equal; this is not surprising since a previous investigation demonstrated that skutterudites with similar compositions and filling levels have thermal expansion coefficients in the same range (see Table 2). The values compare well with those of DD 0.44 Fe 2.1 Co 1.9 Sb 12 or Mm 0.70 Fe 3 CoSb 12 [50].…”

“…Thermal expansion was measured at low (4.2e300 K) and high temperature (300e800 K) as described in Ref. [50]. Young's modulus E Y and Poisson's ratio n were measured via resonant ultrasound spectroscopy, bulk modulus B and shear modulus G were calculated with the data of E Y and n. For DD 0.65 Fe 3 CoSb 12 Young's modulus was also measured in the temperature range of 300e700 K in steps of DT ¼ 100K.…”

“…Vicker's hardness was obtained from a MHT microhardness tester. The Debye temperature, q D , was obtained from a fit to the thermal expansion curve at low temperature [50,51] and from the mean sound velocity [52] using B, G and d (for details of measurements and calculation of mechanical properties see Ref. [53]).…”

“…Thermal expansion for DD 0.65 Fe 3 CoSb 12 was measured at high temperature only; for the temperature range of 400e600 K, a ¼ 10.05 Â 10 À6 K À1 was calculated, a value fitting well in the range of Fe/Co substituted skutterudites [50]. The thermal expansion coefficients for Sr 0.12 Ba 0.18 DD 0.39 Fe 3 CoSb 12 and for Ca 0.20 Sr 0.12 DD 0.39-Fe 3 CoSb 12 ( Fig.…”

Modeling correlated motion in filled skutterudites

“…The improved performance of some multiply filled skutterudites 8,[36][37][38][39][40][41][42][43][44][45][46] may be explained in part from nanodomains with avoided crossings at different qvectors. However, in many cases the concentrations of some filler atom are low and in that case defect scattering should also play an important role.…”