Microstructure of YBCO thin film and its effect on superheating

Previously, we have reported a superheating phenomenon of a YBa₂Cu₃O_x (YBCO) film and studied its mechanism. In this work, we investigated the influence of microstructure on the superheating of a YBCO thin film. Different melting behaviors were observed in situ from YBCO thin films with varied microstructures by using high-temperature optical microscopy (HTOM). These films with different degrees of crystallinity were also characterized by atomic force microscopy (AFM) and X-ray diffraction (XRD). It was found that the crystalline structure features of the seed film have a great influence on the degree of superheating and the melting behavior. A high-quality film with a low fraction of interface defects is believed to be responsible for the high superheating. On the basis of the experimental results from HTOM, AFM, and XRD, the melting and superheating behaviors associated with the film defect structure are well interpreted in terms of the semi-coherent interface-energy theory. PACS 68.35.Md; 68.47.Gh; 68.55.Ac