Spontaneous polarization and/or magnetization in non-ferroelastic domain walls: symmetry predictions

On example of domain walls in α quartz we demonstrate a deduction of wall symmetry and its use in examining the existence of spontaneous polarization in domain walls. We compare these predictions with results of phenomenological theory. Then we present brief summary of a systematic analysis of possible appearance of spontaneous polarization and/or magnetization in non-ferroelastic domain walls.