Enhancement in the electrical transport properties of CaMnO3via La/Dy co-doping for improved thermoelectric performance

Abstract

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_xDy_xCa_1−2xMnO₃ {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 Mn³⁺ 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_0.1Dy_0.1Ca_0.8MnO₃ and the maximum value zT obtained was 0.122 at 1070 K for La_0.075Dy_0.075Ca_0.85MnO₃.