EFFECT OF OXYGEN OVER-DOPING ON T-C AND R(S) OF YBCO FILMS

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, T-c's were degraded to as low as 85K and R(s)'s to >10 m Omega (at 77K and 10 GHz). Re-annealing at 450 degrees C at experimentally optimized oxygen pressures raised T-c's significantly in all cases but had only a marginal effect on R(s) values. Large improvements in R(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-c's of >90K and R(s)'s of less than or equal to 0.5 m Omega (at 77K and 10 GHz) were prepared.