Y and La Doping in CaMnO₃ Compounds: Effects of Dopant Identity and Amount on Charge Transport Kinetics

Enhancing electronic transport properties of thermoelectric oxides is of great technological importance. Oxides are promising candidates for waste heat harvesting at elevated temperatures as well as for electricity generation in low-power applications. To this purpose, fundamental understanding of their electrical and thermal conduction mechanisms is essential. Herein, the conduction mechanism of CaMnO₃ materials is focused on and how dopant identity and amount alter the kinetic properties of charge transport is investigated. Ca_1−xR_xMnO₃ compounds with R = Y and La are synthesized, where 0 ≤ x ≤ 0.13, and the electrical conductivity and Seebeck coefficient for temperatures ranging from 300 to 1050 K, indicating that Y-doped compounds are usually more conductive than their La-doped counterparts, are measured. Analysis of both in terms of the small polaron hopping model reveals that Y doping reduces conduction activation energies, resulting in higher electrical conductivity and charge carrier mobility. Remarkably high values of thermoelectric power factor for the Ca_0.97La_0.03MnO₃ compound, for example, 300 μWm⁻¹ K⁻² at 1050 K are observed; furthermore, these values are preserved for a wide temperature range, rendering this compound a good candidate for heat-to-electrical power generation at elevated temperatures.