The absence of twinning in a-orientated YBa2Cu3O7on (001) SrTiO3

Abstract
The authors report X-ray diffraction measurements of epitaxial crystallites in thin films of YBa2Cu3O7 on (001) SrTiO3. They are found to be orientated with either the a or c axis normal to the substrate surface, but no reflections from b-orientated crystals are observed. This means that not only are b-orientated crystals not present, but also that the a-orientated crystals are free from a-b twins. It is proposed that this is due to substrate-induced strain.