Antiphase boundaries and their interactions with domain walls in ferroelastic-ferroelectric Gd2(MoO4)3

Antiphase boundaries (APB's) in ferroelastic-ferroelectric Gd2(MoO4)3 have been observed by etching single- and multiple-domain crystals. These boundaries form closed loops, or terminate on dislocations, external surfaces, or on domain walls. They can be generated and annihilated by moving domain walls. Space-group symmetry arguments show that APB's can exist in Gd2(MoO4)3. The crystals structure of ferroelastic-ferroelectric Gd2(MoO4)3 is discussed to describe the atomic distortions within domain walls and APB's. This qualitative analysis suggests that the free energy of an APB is of the order of the free energy of the domain wall.