Orthorhombic-tetragonal transition in twin-free (110)YBa2Cu3O7films

Abstract

Twin-free (110) ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ films have been grown by pulsed laser deposition on vicinal (110) STO substrates making use of a double ${\mathrm{PrBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ template layer. Such samples offer a unique opportunity to analyze the physics of the tetragonal-orthorhombic transition and of strain relaxation, and to investigate the fine details of the film-substrate alignment. Mapping of relevant regions of reciprocal space has been performed by x-ray diffraction, and a clear interpretation of the complex experimental data has been obtained after attentive analysis. The presence of a strained layer characterized by an angle $\ensuremath{\gamma}>90\ifmmode^\circ\else\textdegree\fi{}$ between the $a$ and $b$ axes has been observed. The details of the tetragonal-orthorhombic transition have been investigated by repeating reciprocal-space mapping $(a)$ after oxygen depletion of a measured sample, and $(b)$ after restoring the former oxygen content. The mechanisms of detwinning, strain relaxation, and epitaxial alignment taking place during the tetragonal-orthorhombic transition are discussed in detail.