Elastic modulus, biaxial fracture strength, electrical and thermal transport properties of thermally fatigued hot pressed LAST and LASTT thermoelectric materials

Harvesting of waste heat may lead to macrocrack and/or microcrack damage accumulation in thermoelectrics. No studies in the open literature address the thermal fatigue of any thermoelectric material. This study characterizes the thermal fatigue behavior for two PbTe-based thermoelectric materials, n-type LAST (lead–antimony–silver–tellurium) and p-type LASTT (lead–antimony–silver–tellurium–tin). The mechanical properties (fracture strength, elastic moduli) were evaluated for up to 200 thermal fatigue cycles. In addition, the electrical and thermal transport properties were evaluated for n- and p-type specimens for thermal cycling. The elastic moduli were relatively insensitive to thermal fatigue treatment. The fracture strength, σf, of the thermally fatigued LASTT specimens was in a band of from 25 to 40 MPa while σf of the thermally fatigued LAST ranged from 15 to 38 MPa. The thermopower and electrical conductivity of LASTT samples showed small deviations from the low temperature trend near 600 K and the data repeated well after the first temperature cycle for all samples. For the n-type LAST samples, the electrical conductivity and thermopower showed larger deviations from the low temperature trend near 500 K with some samples requiring several temperature cycles before showing repeatability in the data, suggesting a possible secondary phase in the samples. - Highlights: ► Thermoelectric waste heat recovery applications involve thermal fatigue. ► No thermal fatigue data for thermoelectrics is available in the literature. ► This study includes thermal fatigue data two PbTe-based thermoelectrics. ► The fracture strength the thermally fatigued LASTT ranged from 25 to 40 MPa ► The fracture strength the thermally fatigued LAST ranged from 15 to 38 MPa.