THERMOPOWER OF SINGLE-CRYSTAL ND-1-X(SR,PB)(X)MNO3-DELTA

We report measurements of the thermopower of the single-crystal mangan ite perovskite Nd-1-x(Sr,Pb)MnO3-delta from 4.2 to 350 K at zero and f inite magnetic field. The sign and magnitude of the thermopower above the magnetic transition are doping dependent. The magnitude of the the rmopower drops sharply below the transition to the magnetically ordere d state. At lower temperatures the thermopower changes sign from negat ive to positive with decreasing temperature in the range 100-150 K. Im plications for the temperature-dependent electronic structure and scat tering processes in this temperature range are discussed. The high-tem perature behavior is interpreted within a lattice polaron model. Furth er analysis suggests a form of variable-range hopping conduction at hi gh temperatures.