High-Temperature thermoelectric properties in the La_2-xR _xCuO₄ (R: Pr, Y, Nb) ceramics

La_2-xR_xCuO₄ (R: Pr, Y, Nb) polycrystalline ceramics have been prepared by a spark plasma sintering process. Analysis of the microstructure and phase composition shows that pure La ₂CuO₄ ceramics with a high density can be obtained, and no impurity phases appear. All the samples exhibit a metal-semiconductor transition behavior at ∼750 K, which could be ascribed to the decreasing charge density as a result of loss of oxygen atoms and various conduction mechanisms in these La₂CuO₄-based ceramics. Our results indicate that the La_1.98Y_0.02CuO₄ ceramics show large thermoelectric power ∼1.0 × 10^-3 μW·(m·K²)^-1, and the evaluated ZT can reach 0.17 at 330 K, which potentially make them useful for thermoelectric applications.