REACTIVE COEVAPORATION OF YBACUO SUPERCONDUCTING FILMS

Growth conditions for YBaCuO thin films are investigated. Films have been made by reactive e-beam coevaporation using three metal sources. In the best cases, as-made films are superconducting with T(c)'s (R = 0) up to 90 K and J(c)'S (at 4.2 K) above 10(7) A/cm2. Oxygen pressure, deposition temperature, as well as compostional dependencies of the films are presented. It is found that in conditions of lower oxygen, pressure films with average composition off the 1-2-3 stoichiometry have higher T(c)'S. For pressure < 10 mTorr, the highest T(c) obtained is for Ba/Y deposition ratio less-than-or-equal-to 1.4. The morphology and impurity phases of these films are examined. The Ba-deficient films have oriented CuYO2 and CuO as the dominant impurity phases. C-axis lattice parameters (c0) are also examined. It is found that for a given T(c), films made at lower pressure have C0'S which are expanded compared to the films made at higher pressures (> 100 mTorr). The expanded C0'S for these films cannot be reduced by a low temperature oxygen anneal. We suggest that metal-atom point-like defects are quenched into these films and we discuss a particular Ba-for-Y substitution model.