Thermoelectric power studies on Nd1.82-xSrxCe0.18CuOy:x<=0.18 superconductors

Thermoelectric power (S) studies on a Nd1.82-xSrxCe0.18CuOy:x less than or equal to 0.18 superconducting system in the temperature range 35-250 K are reported here. In the x=0.09 sample, synthesized in the reduced environment, the small magnitude of S is highly metalliclike and its sign is negative, a characteristic of electron conduction. The sign of S for the x=0.18 sample shows a crossover below 75 K from negative to positive, in apparent conflict with electronic conduction. Interestingly, after oxygenation this sample exhibits a broadened but positive phonon draglike peak. This oxygenated sample shows overcompensation of the carrier (electron) concentration. Critical analysis of the data suggests that Sr doping seemingly causes a competition between electron- and holelike conduction. The slope dS/dT is, in general, negative suggesting that the main contribution is coming from the diffusive part. The observed thermopower features seem to fall in line with the theoretical curves of Durczewski and Ausloos [Z. Phys. B 85, 59 (1991); Phys. Rev. B 53, 1762 (1996)] based on the inelastic scattering of quasifree electrons by phonons. (C) 1996