MISORIENTATION OF GRAINS AND CRITICAL CURRENT OF HIGH-JC EPITAXIAL YBCO FILMS

Factors which control j(c) values and spread in thin epitaxial YBCO/SrTiO3 films are studied systematically by precision analysis of X-ray diffraction, voltage-current, VCC, and j(c) (B) characteristics (B = 0 divided-by 30 mT). It is shown that there is no direct correlation between the j(c) values of (0,3 divided-by 5).10(6) A/cm2 and the creep activation energy U(c): U(78K) almost-equal-to 0,35eV almost-equal-to 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).