X-RAY-DIFFRACTION STUDIES OF DY1.1BA1.9CU3O7-DELTA(001) AND DY1.3BA1.7CU3OY(001) HIGH-TEMPERATURE-SUPERCONDUCTOR THIN-FILMS

Single-phase Dy1+xBa2-xCu3Oy(001) thin films on LaAlO3(100) substrates were prepared by molecular-beam deposition and post annealing and they were studied by x-ray-diffraction (XRD) and resistivity measurements. The values of lattice constant c0 were determined after correcting for sample displacement errors in the XRD measurements. For an epitaxial Dy1+xBa2-xCu3Oy(001) film, which showed the onset of superconductivity at 53 K, the lattice constant c0 was determined as 11.592 +/- 0.018 angstrom. Similar superconducting behavior and same lattice parameter c0 have been observed for bulk Eu1.3Ba1.7Cu3Oy by Iwata et al. [Jpn. J. Appl. Phys. 26, L2049 (1987)]. Bulk Dy1Ba2Cu3O7-delta and Eu1Ba2Cu3O7-delta have almost the same lattice parameters. Hence the value of x in the Dy1+xBa2-xCu3Oy(001) thin film was derived as 0.3 (uncertainty = -0.03, + 0.05). The Dy1.1Ba1.9Cu3O7-delta(001) thin film showed complete superconductivity at 89.5 +/- 0.5 K (critical transition temperature, T(c,0)). Its lattice constant c0 was measured as 11.644 +/- 0.006 angstrom. Again, the composition was determined by comparison with lattice parameter (c0) and T(c,0) of bulk Eu1.1Ba1.9Cu3Oy as reported by Iwata et al. Since this film is a 90-K superconductor, it is labeled as Dy1.1Ba1.9Cu3O7-delta instead of Dy1.1Ba1.9Cu3Oy (uncertainty in the value of x = 0.03, + 0.05).