Electric field-induced intersections of 90° domain walls in tetragonal ferroelectric crystals

Intersections of the permissible 90° domain walls in tetragonal crystals were analyzed and the fifteen combinations were classified into two major groups. Group A is characterized by a 90° intersecting angle and a 〈001〉 intersecting line while group B is characterized by a 60° intersecting angle and a 〈111〉 intersecting line. When viewed along the 〈001̄〉 direction of thin crystals, the projected images of these intersections appear in four configurations. Electrical charges due to the termination of domains and elastic distortion due to the tetragonality of the lattice structure are introduced at the intersections. Three out of the four configurations of intersections were experimentally identified. The one absent was interpreted as unfavorable under in-plane electric fields. The intersection was observed to lead to the formation of partial dislocations and microcracks. It is proposed that the atomic shifts during 90° domain switching initiate the dislocation formation and the stored elastic energy at intersections is responsible for the microcrack formation.