Young's modulus as a function of composition for an n-type lead–antimony–silver–telluride (LAST) thermoelectric material

Abstract

For 17 cast lead–antimony–silver–telluride (LAST) thermoelectric specimens (representing 14 different chemical compositions), a combination of Vickers and Knoop microindentation techniques were used to determine the composition-dependent Young's modulus, E, which ranged from 24 to 68 GPa. Following microindentation, independent nanoindentation measurements were also performed on 10 of the 17 specimens. In the literature, for pseudobinary joins in ternary or quaternary compounds (with the compositions A _x B_{1– x} C or A _x B_{1– x} CD, respectively), changes in the Young's modulus have been expressed as quadratic functions of the compositional parameter x. In this study, we extend the quadratic functional form to a paraboloid in four composition variables to describe composition-dependent changes in E for the LAST compounds. Also, the composition-dependent changes in LAST are compared to the trends observed in the literature for E and bulk modulus for systems described by a single compositional variable.

Acknowledgements

The authors acknowledge the financial assistance of the US Department of Energy Grant DE-FC26-04NT42281 and Office of Naval Research MURI Grant number N000140310789. The authors also thank the Advanced Microscopy Center at Michigan State University for the use of the SEM facility and Mingfei Li (Center for Statistical Training and Consulting, MSU) for her assistance in statistical analysis. The authors also acknowledge helpful conversations with Professor S. D. Mahanti and Professor D. T. Morelli of Michigan State University and Professor M. G. Kanatzidis of Northwestern University.