Processing and enhancement of thermoelectric performance of Nb doped ZnO (NZO) ceramics

Abstract

In this investigation, we extensively studied the effect of various parameters on the processing, microstructure, sintering and thermoelectric characteristics of ZnO ceramics. Different Nb-doped ZnO-based ceramics, ranging from 0 to 0.25 wt %, were fabricated and sintered at the temperature of 1450 °C for 2 h in an inert atmosphere of argon (Ar). Various characterizations were employed to discern the performance attributes of these ceramics, encompassing phase analysis, densification, and microstructure evaluations. Thermal conductivity properties were studied from room temperature up to the temperature of 800 °C. Thermoelectric properties and efficiency of the sintered ceramics were evaluated across the temperature range of 100–800 °C. Results indicated that the incorporation of Nb into ZnO ceramics resulted in a harmonious structure due to the attained homogeneous and complete solid solution diffusion reaction. It was found that the optimal values for thermal conductivity, electrical resistivity, and thermoelectric properties were achieved at 0.15 wt % Nb doping. ZnO doped ceramics exhibited typical behavior of n-type semiconductors, showcasing exceptional thermoelectric properties at elevated temperatures. Our findings indicate that native defects, such as oxygen vacancies (OV), contribute to decreased band gap energy values and increased carrier concentration, thereby enhancing electrical conductivity and power factor. Hence, this study underscores the viability and practicality of Nb-doping ZnO sintered in an argon atmosphere as an effective approach to enhance its thermoelectric performance.