Thermoelectric Properties of Perovskite-Type Oxide Ca-Mn-O System in Relation to A-Site Vacancies

The orthorhombic perovskite-type oxide systems, Ca1-xNdxMnO3 and Ca1-xNd2x/3 square x/3MnO3 (square indicates A-site vacancy) were synthesized by a standard ceramic technique. Thermoelectric properties such as Seebeck coefficient (S), electrical conductivity (sigma) and thermal conductivity (k) were evaluated as functions of temperature (T) and composition (x). The electrical conductivity increased and the absolute Seebeck coefficient decreased with increased composition, in both the systems. Jonker plots revealed that the insertion of A-site vacancies improved the carrier mobility of Perovskite-type oxides without resulting in a change in their carrier concentration. This insertion induced low thermal conductivity owing to the atomic unbalance of the crystal structure. A-site vacancies are key factors in obtaining higher electrical conductivity and lower thermal conductivity.