Critical thickness and effective thermal expansion coefficient of YBCO crystalline film

Critical thickness for crack formation has been determined for the YBCO crystalline film deposited on the SrTiO3 (STO) substrate by the liquid phase epitaxial (LPE) method. As-prepared films, even more than 4 mu m in thickness, have no visible cracks, while oxygen-annealed films show apparent crack propagation depending on the film thickness, leading to the estimation of critical thickness of about 1.35 mu m. Films formed on MgO buffered STO substrates have almost the same critical thickness. The effective thermal expansion coefficient of YBCO crystalline film has been deduced to be 13.4 x 10(-6)/K by considering thermal expansion of the substrate and the YBCO film, which causes internal tensile stress and crack formation in the film. (C) 1998 Elsevier Science B.V. All rights reserved.