The effect of stress on thermoelectric properties of flexible Mg3Bi2 thin films

Abstract

Mechanically flexible thermoelectric materials are of importance for energy harvesting and powering portable and wearable devices. Stress is often disregarded in investigations of thermoelectric properties, despite the fact that it is increasingly important for flexible devices, given the known but often overlooked correlations between stress and physical properties. To investigate the effects of stress on the thermoelectric properties of Mg3Bi2, we synthesized thin films between ambient temperature and 190 °C using magnetron sputtering. Polymeric and ceramic substrates with a wide range of thermal expansion coefficients were used to grow thin films with varied thermal stress. The crystal structure, morphology, and transport properties of the films were explored. The results indicate that low to moderate stress is beneficial for the power factor, ranging from 0.2 to 152 μW m−1 K−2 at zero thermal stress and 46 MPa, respectively. This highlights the importance of stating stress with the thermoelectric results and could help explain the extensive scatter of literature values reported for the same thermoelectric systems.