ICT2014 Abstracts

Bismuth telluride is a widely used thermoelectric material for waste heat recovery or power generation applications at temperatures below 200°C.   Single crystalline BiTe materials exhibit higher figure of merit zT parallel to the c-axis, however the crystalline planes are also weakly bonded in this direction and they tend to crack easily when subjected to thermal cycle stresses.  For this reason, polycrystalline BiTe materials with higher mechanical strength are preferred in these applications.  To improve the zT of polycrystalline BiTe materials, different processing methods such as hot rolling are deployed to obtain preferred grain orientation and thus obtain higher zT in that direction.  Understanding the mechanical behavior of the materials is important to improve the reliability of the components.  In this work we present mechanical strength properties of p and n type polycrystalline bismuth telluride rods tested in two different grain orientations.   Micro indentation tests and three point bend tests were performed on these rods.   Results show a clear dependence of mechanical strength on the grain orientation for both p and n type bismuth telluride samples.  Corroborating microstructure observations of the fracture surfaces are presented which show the relationship of strength dependence on grain orientation.