Optical Observation of the First-Order Transition of Barium Titanate Single Crystal at the Curie Point

This first-order transition of Barium Titanate single crystal was observed optically at the Curie point of about 120°C by polarizing microscope, and the domain boundary movement was recorded by 16 mm motion picture. The crystal was so called c-plate, and the area and the thickness were about 0.1 mm 2 and 0.03 mm respectively. With increasing temperature, no change was observed up to the Curie point, but at about 120°C the domains begin to move rapidly and discontinuously and the heterogeneous transformation of c-plate to a-plate occurs. Then discontinuous and rapid changes of a-plate to cubic phase occur, and the transition is finished. During this transition, we observed some interesting domain patterns, caused by the penetration of two perpendicular domains.