The Mechanical Properties of Inorganic Thermoelectric Materials: A Review on Characterization Methods and Correlations

The conversion of thermal energy into electricity can be successfully applied by novel renewable energy known as thermoelectricity (TE). Such thermoelectric generators (TEGs) are currently at a technological readiness level (TRL) of 3–5 (out of a level of 10) approaching laboratory prototypes. One of the major setbacks to achieve higher TRLs is the fact that the focus of research is concentrated on improving the electronic/transport properties (mainly affecting the figure of merit – ZT) of the materials, while the research on the mechanical properties and the material‘s ability to adhere service conditions was left behind. Information about the mechanical properties of TE materials – elastic constants (e. g. Young's modulus and Poisson's ratio), strength, and fracture toughness – are paramount necessities (but not the only ones) for approaching practical TEGs. The elastic constants provide an understanding of the material‘s stiffness, while the strength and fracture toughness provide the loading conditions the material can endure. This work summarizes the various mechanical properties and measuring methods along with all up-to-date published data of these properties for inorganic TE materials. This work aims to expose the TE community to the under-looked and nearly untreated field of research. Also, for the first time, a statistical analysis of the collected data was employed to highlight cross relations between mechanical, and physical properties and those who had a high Pearson's correlation parameter are presented. These correlations in turn have the potential to expedite the development and screening of inorganic TE materials for the various applications needed.