Thermoelectric properties of hot-pressed Ruddlesden-Popper phases CaO(CaMnO3)m

Abstract

We investigated the Ruddlesden-Popper series CaO(CaMnO3)m with m = 1, 2, 3, ∞, to study the impact of the varying amounts of CaO layers on their thermoelectric properties. Previous studies showed that highly dense samples are difficult to obtain due to the refractory nature of these materials. In this study, we managed to obtain dense pellets during a classical hot-pressing step, if and only if the samples were subjected to extended ball-milling prior to pressing, resulting in crystallite sizes of 30–35 nm after hot-pressing. The sample with the largest amount of CaO layers (m = 1) had the lowest electrical and thermal conductivity, and the highest Seebeck coefficient, as predicted. Ultimately the perovskite CaMnO3 (m = ∞, no CaO layers) exhibited the best thermoelectric properties.