Enhancing electrical properties in CaMnO3-based ceramics: The impact of single doping with different elements

Abstract

This study explores the effect of single doping with different rare earth elements (Y, La, and Yb) on the structural, morphological and electrical properties of CaMnO₃ bulk ceramics, aiming to improve their thermoelectric performance. Ca_(1-x)R_xMnO₃ (R = Y, La, Yb; x = 0, 0.05, 0.10) samples were synthesized via a solid-state reaction. XRD analysis confirmed the thermoelectric CaMnO₃ phase as the major one, with orthorhombic perovskite structure. Small amounts of secondary phases (CaMn₂O₄ and Mn₂O₃) were also detected in some doped samples. The addition of dopants influenced the unit cell parameters, producing a shift to lower 2θ angles, confirming their incorporation into the ceramic structure. SEM micrographs revealed a significant reduction in grain size upon doping. Electrical resistivity measurements showed a metallic behavior for all doped samples. The Y-doped samples exhibited the highest resistivity values while the Yb-doped samples showed the lowest values (6.8 mΩ cm for the 0.10 doped one), which are among the lowest found in literature for this compound. The Seebeck coefficient values show minor changes for 0.05 doped samples when they decreased with increasing concentration of dopant. Consequently, the highest values were observed for 0.05-doped sample (−215 µV/K), independently of the dopant. This value is much higher than the ones typically reported in the literature. The highest value of the power factor was calculated for the 0.05 Yb doped sample, reaching approximately 0.56 mW/K²·m at 800°C. This value is higher than the best presented in the literature for this compound, to the best of our knowledge, and suggests that Yb³⁺ doping greatly enhances the high-temperature thermoelectric performance of bulk CaMnO₃ ceramics, making it a promising dopant for high-efficiency thermoelectric materials.