We report the first observation in direct space of a manifestation of the memory effect specific to incommensurate (INC) materials. It is found, using transmission electron microscopy, that barium sodium niobate samples cooled rapidly after annealing in the INC phase exhibit at room temperature two distinct regions with different configurations and spacings of discommensurations. These results are correlated to x-ray diffraction data.

• Received 10 February 1987

DOI:https://doi.org/10.1103/PhysRevB.35.8884