Nd_1·86Ce_0·14CuO_4−y is superconducting below about 20 K and electrons are considered to be responsible for superconductivity in these materials as in the case of Ln_2−xCe_xCuO_4−y and Ln_2−xTh_xCuO_4−y. Structurally these materials are not very different from thep-type superconductors La_2−xSr_xCuO_4−y. In both these types of superconductors, the parent compounds are antiferromagnetically-ordered insulators. The induction of holes or electrons by substitution destroys magnetic interactions and brings about superconductivity. Peng and coworkers have studied the resistivity variation of both superconducting and nonsuperconducting Nd_1·85Ce_0·15CuO_4−y and have found a decrease in resistivity with temperature, obeying a lnT dependence in the superconducting samples. Such a variation was not seen by them in the nonsuperconducting samples. They ascribe the lnT variation seen in their superconducting samples to arise from magnetic scattering of electrons. To study whether such an effect exists, Nd_1·86Ce_0·14CuO_4−y was subjected to various annealing conditions and the resistivity behaviour is presented here. Our results differ from those of Penget al.

Single-phase 2122 samples of thallium and bismuth superconductors were made by the precursor matrix method. The thermopower of these samples was measured in the temperature range 250 K-T_c. The thermopower was positive and decreased linearly with increasing temperature aboveT_c (onset). The exponential enhancement of thermopower seen in the undoped and doped YBCO was not observed in these samples. The linear variation of thermopower can be explained on the basis of either a two-band model or a narrow band model.

The thermopower of single-phase samples of Nd_1·85Ce_0·15CuO_4−y was measured from 250 K down to 10 K. The as-prepared sample was not superconducting. It had a negative thermopower at 250 K, whose magnitude increased as temperature was decreased to 95 K. A further reduction in temperature caused a decrease in magnitude of thermopower. The sign of the thermopower changes to positive at 12 K. The superconducting sample also showed the same behaviour but the change of sign now occurred at 40 K. Below 40 K, the thermopower showed a positive peak and reduced to zero at the superconducting transition. These results were compared with previous studies.