Origin of preferential orthorhombic twinning in SrRuO₃ epitaxial thin films

In order to elucidate the driving forces which promote oriented in-plane crystallographic texture in SrRuO₃ thin films deposited on stepped SrTiO₃ substrates, a high-temperature x-ray analysis of both SrRuO₃ thin films and powders was conducted. Structural phase transitions were found at temperatures near 350°C and slightly above 600°C. The transitions are tentatively indexed as orthorhombic to tetragonal and tetragonal to cubic, respectively. These results suggest that SrRuO₃ thin films grow with cubic symmetry. As such, film-substrate interfacial characteristics, rather than a preferred growth direction, are believed to determine the orientation of orthorhombic twins.