Using vacancies to tune mechanical and elastic properties in La3−xTe4, Nd3−xTe4, and Pr3−xTe4 rare earth telluride thermoelectric materials

Abstract

Elastic and mechanical properties in advanced RE3−xTe4 (RE = La, Pr, Nd) thermoelectric materials are found to depend considerably on cation vacancy concentration x. Increasing x, which simultaneously reduces charge carrier concentration from metal-like to semiconductor-like, leads to significant stiffening of elastic constants due to charge carrier effects. The coefficient of thermal expansion in La3−xTe4 determined by high temperature X-ray diffraction correspondingly decreases with x, indicating that thermal expansion may be tuned by x in RE3−xTe4 materials systems. Vickers indentation hardness and fracture toughness tests show similarly significant effects of x on hardness and mode I fracture toughness, both of which decrease with increasing x. The mechanical property trends are counter-intuitive and merit further investigation, but demonstrate overall that higher x in RE3−xTe4 leads to more brittle behavior. The combined results show the importance of intrinsic defects in RE3−xTe4 and the potential to tune the mechanical performance of RE3−xTe4 for practical implementation in next-generation thermoelectric devices.