The temperature dependence of thermal expansion for p-type Ce_0.9Fe_3.5Co_0.5Sb₁₂ and n-type Co_0.95Pd_0.05Te_0.05Sb₃ skutterudite thermoelectric materials

Abstract

During waste heat recovery applications, thermoelectric (TE) materials experience thermal gradients and thermal transients, which produce stresses that scale with the TE material's coefficient of thermal expansion (CTE). Thus, the temperature-dependent CTE is an important parameter for the design of mechanically robust TE generators. For three skutterudite thermoelectric compositions, n-type Co_0.95Pd_0.05Te_0.05Sb₃ (with and without 0.1 at. % cerium doping) and p-type Ce_0.9Fe_3.5Co_0.5Sb₁₂, the CTE was measured using two methods, i.e. X-ray diffraction on powder and bulk specimens and dilatometry on bulk specimens. Each bulk specimen was hot pressed using powders milled from cast ingots. Between 300 K and 600 K, the mean CTE values were 9.8–10.3 × 10⁻⁶ K⁻¹ for the non-cerium-doped n-type, 11.6 × 10⁻⁶ K⁻¹ for the 0.1 at. % cerium-doped n-type and from 12.7 to 13.3 × 10⁻⁶ K⁻¹ for the p-type. In the literature, similar CTE values are reported for other Sb-based skutterudites. For temperatures >600 K, an unrecovered dilatational strain (perhaps due to bloating) was observed, which may impact applications. Also, the submicron particle sizes generated by wet milling were pyrophoric; thus, during both processing and characterization, exposure of the powders to oxygen should be limited.

Keywords:

• thermal expansion
• X-ray diffraction
• inclusion
• thermoelectric
• skutterudite

Acknowledgements

Work performed after September 2010, a part of the “Revolutionary Materials for Solid State Energy Conversion Center,” an Energy Frontiers Research Center, was funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences under award number DE-SC0001054. Research prior to August 2010 was supported by via US Department of Energy Grant DE-FC26-04NT42281. CTE and XRD measurements were conducted through the Oak Ridge National Laboratory's High Temperature Materials Laboratory User Program, sponsored by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program.