Lateral orientation relationship between YBa2Cu3O7−x thin films and MgO(100) and LaAlO3(102) substrates

Thin films YBa2Cu3O7−x (YBCO) were grown epitaxially on MgO(100) and LaAlO3(102), respectively, by pulsed KrF excimer laser ablation. The c-axis of YBCO films was found to be perfectly perpendicular to the plane of substrates used. Combined measurements of X-ray pole-figures and Laue diffraction patterns show that two sets of orientation relationships exist between the a−b plane of YBCO films and both substrates. For the MgO(100) substrate, the a-axis of YBCO films is parallel to either the [001] or [011] directions of the substrate. The latter is more preferential, possibly due to less mismatch between YBCO(300) and MgO(220). In the case of the LaAlO3(102) substrate, the a-axis of the YBCO films is aligned either in the [010] or in the [2̄21] direction of the substrate. A small lattice mismatch of 0.3% favors the latter case.