The Difference Between Thermo- and Pyroelectric Co-Based Rare-Earth (Nd, Y, Gd, Ce) Oxide Composites Measured Using a High Temperature Gradient
The Seebeck voltage US of cobalt-based oxide composites containing rare-earth elements such as Nd, Y, Gd, and Ce was measured under high temperature gradients of up to ΔT = 700 K, as well as its time dependence US(t). The closed-circuit electric current as a function of Seebeck voltage IS(US) or time IS(t) was used for further characterization. While Nd2O3 + CoO and Y2O3 + CoO showed linear n-type US(t) behavior, as it is usual for thermoelectrics, Gd2O3 + CoO exhibited large hysteresis. For both Gd2O3 + CoO and Ce2O3 + CoO, a significant time dependence of the electric current I(t) was measured, indicating pyroelectric material behavior with large capacitance. Both anomalies became smaller when Fe2O3 was added, but became more apparent in Nd2O3 + CoO and Y2O3 + CoO when Al2O3 was added. This behavior can be explained by electron pull-out into the interfacial space-charge region, which is considered as a material phenomenon with great potential for further development.