PROPERTIES OF POLYCRYSTALLINE SAMPLES OF ND2-XCEXCUO4 FROM A SOL-GEL PRECURSOR

Polycrystalline samples of Nd2-xCexCuO4-y(0.0 less than or equal to x less than or equal to 0.17) obtained from a sol-gel precursor were sin tered below the eutectic temperature and reduced under different condi tions. From the results of x-ray powder diffraction, the tetragonal T' structure is preserved for Ce content up to x = 0.17. A decrease in t he lattice parameter c and a small increase in the lattice parameter a are observed with increasing Ce concentration. Electrical resistance R(T) measurements performed on reduced samples with x greater than or equal to 0.12 reveal superconducting behavior below T approximate to 2 5 K. We also found that all reduced samples display a striking double resistive superconducting transition and that the zero resistance stat e is achieved through two distinct drops in R(T) at upper and lower tr ansition temperatures T-ci and T-cj. The upper transition temperature T-ci has a maximum for Ce concentration x = 0.14, which is independent of the reduction process. The lower transition temperature T-cj is ob served in reduced samples with Ce content x greater than or equal to 0 .14 and decreases monotonically with increasing Ce concentration. Magn etic susceptibility measurements confirm bulk superconductivity in sev eral reduced samples, and a significant diamagnetic contribution is on ly observed for temperatures below T-cj. The results are discussed wit hin the framework of a granular superconductor model.