Microstructural relationships between 45 degrees [001] tilt bicrystal substrates and epitaxial superconducting films

Microstructures of superconducting thin films epitaxially grown on both sym metric and asymmetric 45 degrees cubic ceramic bicrystal substrates have be en investigated by transmission electron microscopy. The grain boundary (GB ) of the asymmetrically tilted SrTiO3 (STO) substrate is straight with a si ngle (110)/(100) facet, while that of the symmetric 45 degrees bicrystal su bstrate is wavy and contains many asymmetric step-like (110)/(100) nanoface ts. GBs of the superconducting films grown on such symmetric 45 degrees bic rystal STO substrates are composed of only (110)/(100) facets, hence meande r. All the results indicate that the interfacial energy of asymmetrical (11 0/100) is lower than the symmetric configuration (250)/(520) in the STO. A combination using asymmetric 45 degrees bicrystal MgO substrates (another k ind of cubic ceramic that has the same crystal geometric microstructure wit h that of STO and larger thermal expansion coefficient than that of YBa2Cu3 O7-delta (YBCO)) and enhanced lateral growth method, such as liquid phase e pitaxy, enables us to obtain long single facets (about 10 mum long) in YBCO films. (C) 2001 Elsevier Science B.V. All rights reserved.