The effects of the O partial pressure, during annealing, upon twin formation in (110)-oriented thin films - grown on (110) SrTiO3 substrates by pulsed laser deposition - were studied using high-resolution X-ray diffraction with diffraction-space mapping via a 4-circle diffractometer. The films were found to have a structure in which the a and b axes were tilted about 0.5º away from those of the substrate, while the (110) planes remained parallel to each other. A decrease in the in situ O pressure during annealing led to a reduction in twinning. It was finally suppressed in films which were annealed under an O partial pressure of 0.6Torr. The results suggested that twin formation during a tetragonal-to-orthorhombic transformation was controlled by a competition between the uniaxial force which was exerted at the interface by the vicinal substrate surface, and the thermodynamic force which originated from the difference in the lattice parameters for the a and b axes of orthorhombic Cu3Ba2YO7.

Influence of Annealing Oxygen Pressure on In-Plane Epitaxy and Twinning in (110) YBa2Cu3O7-δ Thin Films. X.G.Qiu, H.Koinuma, M.Iwasaki, M.Kawasaki, Y.Segawa: Physical Review B, 1999, 60[1], 707-12