Synchrotron topography of phase transitions in perovskite-like crystals

Abstract

In situ observations have been made of the first-order phase transition occurring at approximately 145 degrees C in a large LaGaO3 single crystal, and the second-order phase transition occurring at approximately 435 degrees C in a large LaAlO3 single crystal, using synchrotron white beam X-ray diffraction topography. In the case of LaGaO3, the high-temperature rhombohedral phase reflections gradually replace the low-temperature orthorhombic reflections as the transition temperature is approached. In the case of LaAlO3, the magnitude of this image shift continuously decreased in magnitude as the temperature approaches the transition point, which along with the gradual distortion of the diffraction pattern, confirms the second-order nature of this transition. As the transition is surpassed, twinning completely disappears in the crystal, as expected, since the twin planes in the rhombohedral phase become mirror planes in the cubic phase.