Misorientation of grains and critical current of high-Jcepitaxial YBCO films

Factors which control J c values and spread in thin epitaxial YBCO/SrTiO 3 films are studied systematically by precision analysis of X-ray diffraction, voltage-current, VCC, and J c (B) characteristics (B=0/30 mT). It is shown that there is no direct correlation between the J c values of (0.3/5).10 6 A/cm 2 and the creep activation energy U: c U(78 K) approximately=0.35 eV approximately=const (J c ) in contrast to the creep model. The direct correlation is obtained between the angular misorientation ( Delta ) of the c-axis oriented grains and J c value of films. A new model of nonuniform critical current distribution is suggested, which describes absolute values of J c and J c (B) dependences completely as a function J c (B,U, Delta ).