Enhancement in the electrical transport properties of CaMnO La/Dy co-doping for improved thermoelectric performance

The untiring endeavour towards green energy is a trending research among the research community. Thermoelectric materials are of vital importance here owing to their emission-free operation. As a righteous candidate, calcium manganate materials are being explored to increase its figure of merit. In this study, the structural, microstructural, electrical transport, and high-temperature thermoelectric measurements of La x Dy x Ca 1−2 x MnO 3 { x = 0.025 (L25D25), 0.05 (L50D50), 0.075 (L75D75), and 0.1 (L100D100)} were systematically performed. The structural confirmation of the synthesised sample was validated using X-ray diffraction, which also revealed the orthorhombic (space group: Pnma ) crystallisation of co-doped samples with no traces of secondary peaks. A significant increase in the unit cell volume was observed with rare earth substitutions. The morphological studies revealed that the prepared samples were highly dense and the grain size was reduced with rare earth concentration. The substitution of La and Dy enhanced the conductivity values of pristine CMO by two orders of magnitude due to the high concentration of charge carriers and the presence of Mn 3+ ions due to rare earth doping. The conductivity increased with rare earth concentrations but diminished for x = 0.1 due to the localization of charges. The Seebeck coefficient values were negative for all the prepared samples, indicating electrons as the predominant carriers over the entire operating range. A minimum κ of 1.8 W m −1 K −1 was achieved for La 0.1 Dy 0.1 Ca 0.8 MnO 3 and the maximum value zT obtained was 0.122 at 1070 K for La 0.075 Dy 0.075 Ca 0.85 MnO 3 . The solid state synthesized La 0.075 Dy 0.075 Ca 0.85 MnO 3 sample shows the highest zT max of 0.122 due to large value of electrical conductivity and large number of grain boundaries in the matrix.