Effect of oxygen over-doping on T/sub c/ and R/sub s/ of YBCO films

Data on bulk YBa/sub 2/Cu/sub 3/O/sub 7-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, T/sub c/'s were degraded to as low as 85 K and R/sub s/'s to >10 m/spl Omega/ (at 77 K and 10 GHz). Re-annealing at 450/spl deg/C at experimentally optimized oxygen pressures raised T/sub c/'s significantly in all cases but had only a marginal effect on R/sub s/ values. Large improvements in R/sub s/ 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 T/sub c/'s of >90 K and R/sub s/'s of /spl les/0.5 m/spl Omega/ (at 77 K and 10 GHz) were prepared.<
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