Temperature-dependent Young's modulus, shear modulus and Poisson's ratio of p -type Ce _0.9Fe _3.5Co _0.5Sb ₁₂ and n -type Co _0.95Pd _0.05Te _0.05Sb ₃ skutterudite thermoelectric materials

Effective models of the mechanical behavior of thermoelectric materials under device conditions require knowledge of temperature-dependent elastic properties. Between room temperature and 600K, resonant ultrasound spectroscopy measurements of three skutterudite thermoelectric materials, i.e. n-type Co0. ₉₅Pd0. ₀₅Te0. ₀₅Sb ₃ (both with and without 0.1 at.% cerium dopant) and p-type Ce0. ₉Fe _3.5Co0. ₅Sb ₁₂, showed that the Young's and shear moduli decreased linearly with temperature at a rate of 0.021GPa/K to 0.032GPa/K, and 0.011GPa/K to 0.013GPa/K, respectively. In contrast, the Poisson's ratio was approximately 0.22 for the three materials and was relatively insensitive to temperature. For temperatures >600K, 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.