Logarithmic temperature dependence of the resistivity of Nd_2-xCe_xCuO_4-y

Abstract

Single phase compounds of Nd_2-xCe_xCuO_4-y(0.14 ≤ x ≤ 0.18) were made by the standard solid state reaction. The as-prepared nonsuperconducting samples were further annealed in various reducing atmospheres to induce superconductivity. All of the samples, except that with a concentration x=0.18, exhibited superconductivity after an annealing treatment at 850°C for 6 h in a vacuum of 10⁻⁵ Torr. Magnetisation measurments confirmed the Meissner fraction to be around 20% for these compounds. Resistivity measurements were performed on samples which were annealed under different conditions. The resistivity showed a ln T dependence, which was prominent in those samples in which superconductivity was not observed. In the samples showing zero resistivity, the ln T term is absent or present with a much smaller coefficient than in the nonsuperconducting samples.