Temperature-dependent Young's modulus, shear modulus and Poisson's ratio of p-type Ce_0.9Fe_3.5Co_0.5Sb₁₂ and n-type Co_0.95Pd_0.05Te_0.05Sb₃ skutterudite thermoelectric materials

Abstract

Effective models of the mechanical behavior of thermoelectric materials under device conditions require knowledge of temperature-dependent elastic properties. Between room temperature and 600 K, resonant ultrasound spectroscopy measurements of three skutterudite thermoelectric materials, i.e. n-type Co_0.95Pd_0.05Te_0.05Sb₃ (both with and without 0.1 at.% cerium dopant) and p-type Ce_0.9Fe_3.5Co_0.5Sb₁₂, showed that the Young's and shear moduli decreased linearly with temperature at a rate of −0.021 GPa/K to −0.032 GPa/K, and −0.011 GPa/K to −0.013 GPa/K, respectively. In contrast, the Poisson's ratio was approximately 0.22 for the three materials and was relatively insensitive to temperature. For temperatures >600 K, the elastic moduli decreased more rapidly and resonance peaks broadened, indicating the onset of viscoelastic behavior. The viscoelastic relaxation of the moduli was least for Ce-doped n-type material, for which grain boundary precipitates may inhibit grain boundary sliding which in turn has important implications concerning creep resistance. In addition, powder processing of the n- and p-type materials should be done cautiously since submicron-sized powders of both the n- and p-type powders were pyrophoric.

Keywords:

• elasticity
• inclusion
• resonance ultrasonic spectroscopy
• thermoelectric material
• anelastic behavior

Acknowledgements

Since September 2010 this research has been supported by the Department of Energy, “Revolutionary Materials for Solid State Energy Conversion Center,” an Energy Frontiers Research Center funded by the US Department of Energy, Office of Science, Office of Basic energy Sciences under award number DE-SC0001054. Prior to August, 2010, the research was funded by US Department of Energy Grant DE-FC26-04NT42281. The authors acknowledge the use of the equipment for CTE, high-temperature RUS and XRD measurements through the Oak Ridge National Laboratory's High Temperature Materials Laboratory User Program, which is sponsored by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program. Ed Timm, Mechanical Engineering Department, Michigan State University, assisted the authors with hot pressing and cutting the specimens.