CHARACTERISTICS OF ND1+XBA2-XCU3O6.5+Y SUPERCONDUCTORS

Five superconductors of the Nd1+xBa2-xCu3O6.5+/-y type (x = 0.00, 0.05, 0.10, 0.15, and 0.20) are prepared. The orthorhombic crystal lattice observed at x = 0 gradually transforms into a tetragonal structure at increasing values of x. Resistivity measurements (dc) show a metal-semiconductor type transition at temperatures above T-c. T-c ranges from 92 to 72 K by increasing values of x from 0.00 to 0.20, respectively. The oxygen content (y) increases with increasing x. Comparison of calculated and experimental values of y suggests that Nd is present in the form of Nd2O3. In contrast to earlier reports, it appears that the behavior observed are due to a mixture of Nd2O3 and NdBa2Cu3O6.5+/-y instead of Nd1+xBa2-xCu3O6.5+/-y suggested earlier.