Abstract
Thermoelectric properties of the tetragonal perovskite-type oxide system Ca2.73-mLnmMnz-2O7-delta (Ln = Nd, La) (0 L.T. m L.T. m 0.l8) were investigated. The a-axis in the tetragonal phase increased with increasing m, while the c-axis decreased with increasing m. It was found that Ca2.73-mLnmMn2O7-delta system shows a n-type semiconductor in the range 0 L.T. m L.T. 0.18 from the measurements of Seebeck coefficient (S), the thermal conductivity (kappa) and the electrical conductivity (sigma) and that the lattice thermal conductivity (kappaL) increases with increasing m. The relationship between the change in the c-axis due to the Ln content (m) and kappaL was linear. From these results, it was speculated that the c-axis plays an important role in the thermal properties. Ca2.63Ln0.09Mn2O7-delta showed the maximum figure of merit of 0.07xl0-3 K-1 at 873 K among the Ca2.73-mLnmMn2O7-delta systems.
