Interlayer for matching crystal lattices in the domain walls of ferroelastic lead orthophosphate

The possible existence of an interlayer with the symmetry of the paraphase in the W and W′ domain walls of lead orthophosphate has been checked from the condition of matching the crystal lattices of adjacent domains. It is shown that two types of interlayers are possible, which possess different symmetries, strain tensors, matrices of the rotation of the coordinate system, thicknesses, and elastic energies. It is shown that the domain-wall energy is proportional to the squared spontaneous deformation.