Abstract
Thermoelectric properties have been investigated for polycrystalline samples of lightly electron-doped perovskite manganites (GdxCaySr1-x-y)MnO3 (0<x<0.1,0<y<1) above room temperature. A detailed studt of the manganites with fixed carrier doping level reveals a direct relationship between the electrical transport phenomenon and the average A-site ionic radius <rA> affecting one-electron bandwidth (W) of Mn 3d-eg band. F or fixed doping level, a maximum in electrocal conductivity is observed for the composition with maximum W, which produces optimal eg-electron transfer between Mn sites. Furthermore, we show that the thermoelectric power, which depends on x, is large (<-150uV/K) in the metallic region of carrier density ˜1021 cm-3. These results indicate that the thermoelectric power factor in lightly electron-doped manganites can be rigorously controlled by x and <rA>. Also, the observed dimensionless figure of merit ZT=0.17 at 1000K in air indicates that this material can be applied to n-type high temperature thermoelectrics.
