Crystallography Journals Online : IUCR Backfile Archive 1948-2001
YBa2Cu3O7 (YBCO) thin films with c-axis orientation on (001) SrTiO3, (001) MgO and (110) NdGaO3 substrates were examined by four-circle diffractometry with Co Kα and synchrotron radiation (λ = 0.1540 nm) using the q-scan technique. Small local film rotations about  have been introduced by two different mechanisms: (1) the orthorhombic/tetragonal phase transition driven by iron substitution or changes of the oxygen content; (2) heavy-ion irradiation (1.4 GeV 238U UNILAC, GSI Darmstadt). In the original orthorhombic state, the (110) axes of film and substrate are parallel so that the (100)film axes form an angle of 0.45° to those of the substrate. With decreasing orthorhombicity, this angle decreases to zero for tetragonal symmetry. Irradiation of the orthorhombic film by heavy ions produces detwinning and leads to a macroscopic preferential parallel alignment of the 〈100〉 axes of film and substrate. This reorientation is completed for a dose between 1011 and 1012 particles cm−2. High-resolution transmission electron microscopy investigations reveal a rotation of crystallites in the ab plane of irradiated samples of up to 3°. For irradiation with 200 (456) MeV 40Ca, no detwinning is observed.
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