GRAIN-MISORIENTATION CONTROL OF THE CRITICAL CURRENT IN HIGH-J(C) EPITAXIAL YBA2CU3O7/SRTIO3 FILMS

A systematic study is reported of physical factors that control the j(c) values of high-j(c) (greater-than-or-equal-to 10(6) A/cm2 at T = 78 K, B = 0) epitaxial YBa2Cu3O7/SrTiO3 films. By x-ray analyses and transport j(c) measurements of 15-20 microbridges produced on the same films, it is shown that the film microstructure is the most important factor controlling j(c). A direct correlation is found between j(c) values and the grain misorientation angle-DELTA, and an exponential dependence j(c)(DELTA) is obtained as j(c)(78 K) = 7 x 10(6) exp(- DELTA/2.4 deg) A/cm2 for DELTA in the range of 0.5-7.0 deg. A model of film critical current is developed in which the grain misorientation highly influences the quantity of weak links in a film.