KONDO EFFECT AND SUPERCONDUCTIVITY IN ND2-XCEXCUO4-DELTA COMPOUNDS

Samples of Nd2-xCexCuO4- (0 x 0.2) were prepared by annealing both in air and under vacuum (10-5 Torr). Powder x-ray-diffraction patterns indicated that all samples consisted of a single-phase Nd2CuO4-type tetragonal structure with crystal symmetry I4/mmm. Electrical resistivity measurements showed that all Ce-doped Nd2CuO4- samples annealed in air and those annealed in vacuum with x<0.17 demonstrate a resistivity minimum (Kondo effect) resulting from the combination of magnetic and phonon scattering. Magnetic susceptibility and electrical resistivity measurements reflect the influence of crystal-field effects below 55 K. The linear temperature-dependent term of the resistivity typical of metallic behavior in the high-Tc oxides exists across the whole range of Ce concentration, with the exception of the host compound Nd2CuO4- , which is an insulator. This indicates that a model of metal-insulator transition is not appropriate in describing the occurrence of superconductivity in Nd2-xCexCuO4- . © 1990 The American Physical Society.