MICROWAVE ABSORPTION STUDIES ON HIGH-Tc SUPERCONDUCTORS AND RELATED MATERIALS VII — ESR OF DPPH COATED ON A THIN BiSrCaCuO FILM FABRICATED ON MgO(100) SUBSTRATE

ESR of DPPH coated on a Bi-Sr-Ca-Cu-O (BSCCO) film (350 Å thick) fabricated on MgO(100) substrate by MOCVD was studied. Temperature dependence of the ESR peak-to-peak linewidth, ΔH pp , and the effect of applied magnetic field on ΔH pp have been studied below about 100 K. The results were compared with those of ESR of DPPH coated on ceramic Y-Ba-Cu-O samples (powder and bulk) made by the MPMG method. The DPPH ESR for the BSCCO film revealed that ΔH pp was independent of applied magnetic field up to about 9 kG. In addition, no similarity between the temperature dependence of the excess ESR linewidth of the DPPH and that of critical current density was found for the BSCCO film. These results for the BSCCO film are different from those for the MPMG YBCO samples.

Reaction mechanism of Y-system superconductors in the MPMG method

The effect of the melt-quenching step on the refinement of Y2BaCuO5 (211) particles, and phase transformations during crystallization in the MPMG (Melt-Powder-Melt-Growth) process were investigated. The quenched powders, which mainly consisted of Y2O3 and BaCu2O2, were transformed into the 211 and liquid phases by way of the YBa2Cu3Oy (123) phase. The transformation was examined on samples quenched from various temperatures. Through crystallographic examination using several kinds of precursors, it has been demonstrated that the addition of platinum, which is a contaminant from the crucible during the first partial melting step in the MPMG method, can refine the 211 particles.