Twinning behaviour in YBCO and PBCO thin films and in PBCO-YBCO superlattices

Abstract It is well established that YBa 2 Cu 3 O 7− x bulk crystals twin when crossing the tetragonal to orthorhombic transition. Much fewer investigations have been performed on thin films, but one expects a strong influence of the strain induced by the underlying substrate. An analysis of this influence has been undertaken by X-ray diffraction and transmission electron microscopy, from a set of specific samples grown by metal-organic chemical vapor deposition: YBa 2 Cu 3 O 7 − x PrBa 2 Cu 3 O 7 − x and YBa 2 Cu 3 O 7− x -PrBa 2 Cu 3 O 7− x thin films and superlattices. Results indicate that thick (> 100 nm) YBCO films on cubic SrTiO 3 (001) substrates exhibit the same twinning behaviour as bulk crystals. For YBCO films grown on orthorhombic YAIO 3 , substrates only one twinning direction is observed. YBCO-PBCO superlattices on SrTiO 3 exhibit an orthorhombic symmetry down to superperiods of 25 A. The superlattices twinning behaviour is also highly dependent on the total thickness of the stacking.