In-situ observation of the domain configurations during the phase transitions in barium titanate

Using a polarizing optical microscope in conjunction with a charged-coupled device camera system, the domain microstructural evolution with respect to temperature in all three phases of BaTiO3 was studied. Along 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 near the same temperature, 125 degrees C. On cooling, the domain structures 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 final transition temperature from orthorhombic to rhombohedral was difficult to determine using this technique. The transition on cooling occurred at -134 degrees C based on a colour change and the disappearance of all the domains. During heating, the domains reappeared at -110 degrees C and remained in a patchwork structure throughout the orthorhombic phase.