Thermal Cycling Behavior of Zinc Antimonide Thin Films for High Temperature Thermoelectric Power Generation Applications.

The zinc antimonide compound ZnxSby is one of the most efficient thermoelectric materials known at high temperatures due to its exceptional low thermal conductivity. For this reason, it continues to be the focus of active research, especially regarding its glass-like atomic structure. However, before practical use in actual surroundings, such as near a vehicle manifold, it is imperative to analyze the thermal reliability of these materials. Herein, we present the thermal cycling behavior of ZnxSby thin films in nitrogen (N2) purged or ambient atmosphere. ZnxSby thin films were prepared by cosputtering and reached a power factor of 1.39 mW m(-1) K(-2) at 321 °C. We found maximum power factor values gradually decreased in N2 atmosphere due to increasing resistivity with repeated cycling, whereas the specimen in air kept its performance. X-ray diffraction and electron microscopy observations revealed that fluidity of Zn atoms leads to nanoprecipitates, porous morphologies, and even growth of a coating layer or fiber structures on the surface of ZnxSby after repetitive heating and cooling cycles. With this in mind, our results indicate that proper encapsulation of the ZnxSby surface would reduce these unwanted side reactions and the resulting degradation of thermoelectric performance.