(111)_p microtwinning in SrRuO₃ thin films on (001)_p LaAlO₃

SrRuO₃ (SRO) thin films grown on (001)p (p = pseudocubic) oriented LaAlO₃ (LAO) by pulsed laser deposition have been characterized using transmission electron microscopy. Observations along the 〈100〉_p directions suggests that although the SRO layer maintains a pseudocube-to-pseudocube orientation relationship with the underlying LAO substrate, it has a ferroelastic domain structure associated with a transformation on cooling to room temperature to an orthorhombic Pbnm phase (a ^- a ^- c ⁺ Glazer tilt system). In addition, extra diffraction spots located at ± 1/6(ooo)_p and ± 1/3(ooo)_p (where o indicates an index with an odd number) positions were obtained in 〈110〉_p zone-axis diffraction patterns. These were attributed to the existence of high-density twins on {111} _p pseudocubic planes within the SrRuO₃ films rather than to more conventional mechanisms for the generation of superstructure reflections.