THERMOELECTRIC-POWER STUDIES ON ND1.82-XSRXCE0.18CUOY-X-LESS-THAN-OR-EQUAL-TO-0.18 SUPERCONDUCTORS

Thermoelectric power (S) studies on a Nd1.82-xSrxCe0.18CuOy:x less tha n 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 redu ced environment, the small magnitude of S is highly metalliclike and i ts 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. Interes tingly, after oxygenation this sample exhibits a broadened but positiv e 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 electr on- and holelike conduction. The slope dS/dT is, in general, negative suggesting that the main contribution is coming from the diffusive par t. The observed thermopower features seem to fall in line with the the oretical curves of Durczewski and Ausloos [Z. Phys. B 85, 59 (1991); P hys. Rev. B 53, 1762 (1996)] based on the inelastic scattering of quas ifree electrons by phonons. (C) 1996 American Institute of Physics.