Superconducting Properties of Tetragonal Nd_1.5Ba_1.5Cu₃O_y: The Effects of Annealing under High Oxygen Pressure

Abstract

Superconductivity in tetragonal Nd 1.5 Ba 1.5 Cu 3 O y was observed by annealing at 450°C under high oxygen pressure. Slight changes in the crystal structure parameters were observed by Rietveld refinements of the X-ray powder diffraction data. The (Ba, Nd)-(Ba, Nd) distance became shorter, and the O(2) atom site shifted from the Cu(1)-O plane toward the Cu(2)-O plane, due to the increase of the oxygen atoms at the O(1) site. The occurrence of superconductivity is considered to be correlated with the increase in carriers which are introduced by the oxygen atoms at the O(1) site.