DETAILED ANALYSIS OF THE ZERO CRITICAL-TEMPERATURE IMPROVEMENT IN MNYBA2CU3O7-DELTA COMPOSITES FROM ELECTRICAL AND STRUCTURAL STUDIES

The study was aimed al investigating in a continuous manner the influe nce of the solid and/or liquid phase sintering on xMn-(1-x)YBCO (where YBCO represents YBa2Cu7O7-delta) composites, with 0.02 less than or e qual to x less than or equal to 0.07. The main result is obtained from resistance vs. temperature measurements; in comparison with the pure YBCO. we show that an improvement in the zero resistance temperature i s obtained at an optimal sintering temperature. whatever the Mn concen tration x of the composite is. From the microstructural study, associa ted with energy-dispersive X-ray analysis, we detect that. in that cas e, particular inclusions are formed, with a constant Mn content probab ly responsible for the zero critical temperature improvement. The inte rpretation is based on the fact that the Mn substitution in the YBCO l attice cannot be fully responsible for this improvement and that the s econdary phases play a role in explaining such a phenomenon.