IN-SITU OBSERVATION OF THE DOMAIN CONFIGURATIONS DURING THE PHASE-TRANSITIONS IN BARIUM-TITANATE

Using a polarizing optical microscope in conjunction with a charged-co upled device camera system, the domain microstructural evolution with respect to temperature in all three phases of BaTiO3 was studied. Alon g a (001) oriented section the domains in the tetragonal phase form 90 degrees domain patterns in an 'a-a' configuration. The transition on heating and cooling between the cubic and tetragonal phases occurred n ear the same temperature, 125 degrees C. On cooling, the domain struct ures in the orthorhombic phase appeared as a long continuous lamellar structure, while on heating the domains formed a 'patchwork' structure . This transition temperature showed a large thermal hysteresis. The f inal transition temperature from orthorhombic to rhombohedral was diff icult to determine using this technique. The transition on cooling occ urred at -134 degrees C based on a colour change and the disappearance of all the domains. During heating, the domains reappeared at -110 de grees C and remained in a patchwork structure throughout the orthorhom bic phase.