The walls of ferroelastic domains in B-Ln2O3

An investigation is made of the ferroelastic transition hexagonal-monoclinic of rare earth oxides. The walls separating the ferroelastic domains are defects in the monoclinic structure. For a defective crystal in the state of quasiplastic deformation, the tensor density description or theory of 'quasi-dislocations' is applied for the case of samarium oxide. This theory is extended to the formal description of an isolated wall separating two domains by a distribution of dislocations, so that the lattice of the one part and the other of the interface corresponds to a simple rotation. The walls are defined in this sense as flexible joints and their existence does not create deformation in the adjacent lattice. Additionally the mechanism is used to analyze certain interactions occurring in simple cases of junctions between walls. (author)