J. R. Gavaler, J. Talvacchio, and R. W. Weinert
Abstrac t- Data on bulk YBa2Cu3O7-x (YBCO) have shown that optimum critical temperatures are obtained in material that has less than the maximum (stoichiometric) oxygen content, x=0. We have prepared films of YBCO that were over-doped with oxygen and have measured their properties. In some of these films, Tc's were degraded to as low as 85K and Rs's to 10 m (at 77K and 10 GHz). Re-annealing at 450C at experimentally optimized oxygen pressures raised Tc's significantly in all cases but had only a marginal effect on Rs values. Large improvements in Rs were obtained in the films which initially had very high surface resistances only by annealing them at higher temperatures. Growth and annealing conditions are described by which YBCO films with Tc's of >90K and Rs's of 0.5 m (at 77K and 10 GHz) were prepared.
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