T.E.M. study of 3-q modulated phase of quartz-type under electric field

Since the 3-q modulated phase of quartz-type (existing in quartz and berlinite) can be predicted to be polar (ferroelectric or pyroelectric) we have performed T.E.M. experiments under an applied external field along z. We observe that ferroelectric switching does occur, the mechanism being a sidewise motion of the ferroelectric walls, the block boundaries. Under the field, there occurs also a slight distortion of the sample inconsistent with symmetries of alpha or beta phases but in agreement with the predicted symmetry 6' of the 3-q modulated phase.