Partial dislocations at domain intersections in a tetragonal ferroelectric crystal

Domain behaviour under electric cycling was examined by transmission electron microscopy in a 〈001〉-oriented 0.65Pb(Mg_1/3Nb _2/3)O₃-0.35PbTiO₃ ferroelectric crystal. Prior to electric cycling, the crystal contained two nonparallel sets of 90° domain walls along the two {110} planes. For the most part, the domain walls remained planar, dividing the crystal into highly regular domain strips. As two nonparallel domain walls approached each other, the domain width tapered down to avoid full contact. Upon repeated electric cycling, the domains were forced into full contact, resulting in direct intersections of 90° domain walls and charged wall segments along the domain intersection. At the domain intersection, partial dislocations were observed along with a stacking fault on a {1̄01) plane. These dislocations had a Burgers vector of 1/2[101] and were of predominantly screw type. It is suggested that the partial dislocations resulted from a shear displacement along [101] in the crystal as the domain switched its polarization to form the intersection.