Effect of O2 partial pressure on post annealed Ba2YCu3O7-δ thin films

This paper reports on epitaxial films of Ba2YCu3O7-δ (BYCO) as thin as 250 Angstrom and with Jc's approaching those of the best in situ grown films which can be formed by co-evaporating BaF2, Y, and Cu followed by a two-stage anneal. High quality films of these thicknesses become possible if low oxygen partial pressure [p(o2) = 4.3 Torr] is used during the high temperature portion of the anneal (Ta). The BYCO melt lie is the upper limit for Ta. The use of low P(o2) shifts the window for stable BYCO film growth to lower temperature, which allows the formation of smooth films with greater microstructural disorder than is found in films grown in p(O2) = 740 Torr at higher Ta. The best films annealed in p(O2)=4.3 Torr have Jc values a factor of four higher than do comparable films annealed in p(O2)=740 Torr. The relationship between the Ta required to grow films with the strongest pinning force and p(O2) is log [p(O2)] (Proportional to) Ta-1, independent of growth method (in situ or ex situ) over a range of five orders of magnitude of p(O2)