NATURE AND AMOUNT OF CARRIERS IN CE DOPED ND2CUO4 .1. HIGH-TEMPERATURE CHARACTERIZATION

DC conductivity, ionic transport number, and thermopower have been mea sured of Nd2-xCexCuO4+/-delta materials (x = 0, 0.05, 0.10, 0.15, 0.20 ) at different temperatures [300 less than or equal to T less than or equal to 900 degrees C] and under different oxygen partial pressures [ 1 atm less than or equal to P(O-2) less than or equal to 3 X 10(-6) at m]. For the most heavily doped samples, the current carriers are elect rons essentially produced by the substitutional defect Ce-Nd(.), while the crystal-gas equilibria involving O-i'' account for a smaller amou nt of carriers. The behavior of Nd1.95Ce0.05CuO4+/-delta is intermedia te between more doped and undoped materials. When coupled with oxygen non-stoichiometry data, the results indicate that the mobility of the electronic carriers exhibits a transition from small-polaron to large- polaron behavior with increasing doping level.