Effects of Pr and Yb Dual Doping on the Thermoelectric Properties of CaMnO3

Abstract

There has been research on CaMnO₃ with natural abundance, low toxicity, and low cost as promising candidates for n-type thermoelectric (TE) materials. In this paper, Ca₁_-_2xPr_xYb_xMnO₃ with different Pr and Yb contents (x = 0, 0.01, 0.02, 0.03, 0.04 and 0.05) were synthesized by means of coprecipitation. With X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM), researchers characterized the phase structure and morphology of all the samples. The oxidation states of manganese were determined by X-ray photoemission spectroscopy (XPS). The role of Ca-site dual doping in the TE properties was also investigated. Increasing the Pr and Yb contents leads to decreases in the electrical resistivity and Seebeck coefficient, leading to a power factor of 3.48 × 10^-4 W·m^-1·K^-2 for x = 0.04 at 773 K, which is its maximum. Furthermore, the thermal conductivity (κ) decreases with increasing x, and κ = 1.26 W m^-1·K^-1 is obtained for x = 0.04 at 973 K. Ca_0.92Pr_0.04Yb_0.04MnO₃ exhibit a ZT (thermoelectric figure of merit) value of 0.24 at 973 K, approximately 3 times more than that of the pristine CaMnO₃. Thus, the reported method is a new strategy to enhance the TE performance of CaMnO₃.