Investigation of the phase transitions of ferroelectric KIO3 and KNbO3 crystals by optical diffraction

Optical diffraction is reviewed as a technique for investigation of the phase transitions in crystals with a multidomain structure. It has been used to study the phase transitions in KIO₃ and KNbO₃ single crystals. Strong optical diffraction bands resulted from electric domains in KNbO₃ crystals and their change with temperature were observed when a laser beam passed through the crystals. The diffraction patterns observed changed abruptly at 427°C, 223°C, and -50°C respectively, at which KNbO₃ crystals undergo structural phase transitions. It is considered that the change of the diffraction patterns with temperature is due to change of the electric domains in the crystals.