Porosity dependence of elastic moduli in LAST (Lead-antimony-silver-tellurium) thermoelectric materials

Porosity in thermoelectric materials affects the thermal, electrical and mechanical properties of the materials. In this study, the resonant ultrasound spectroscopy technique was used to determine the Young's modulus, E, shear modulus, G, and Poisson's ratio, v, of 12 hot pressed and five cast polycrystalline specimens of the thermoelectric material LAST (lead-antimony-silver-tellurium) as a function of volume fraction porosity, P, for P ranging from 0.01 to 0.14. A least-squares fit of the Young's and shear moduli data to the relationships E = E-D(1 - b(PE)P) and G = G(D)(1 - b(PG)P), respectively yielded E-D = 58.4 +/- 0.6 GPa and G(D) = 23.0 +/- 0.2 GPa, where E-D and G(D) are the estimated Young's modulus and shear modulus at room temperature for theoretically dense specimens, respectively. The unitless, material-dependent constants b(PE) and b(PG) were b(PE) = 3.5 +/- 0.2 and b(PG) = 3.5 +/- 0.2. (C) 2009 Elsevier B.V. All rights reserved.