Optical and interferometric studies on ferroelectric guanidinium aluminum sulphate hexahydrate cleavages and their etch patterns

GASH single crystals have been cleaved along (0001) planes and the cleavage faces have been studied by multiple-beam interferometry. The cleavage faces have also been chemically etched and the etch patterns studied optically. By etching a cleavage successively for three different periods it was found that the bottoms of the point-bottomed pits follow a linear etch path. Correspondence both in the etch patterns on matched pairs and in the etch patterns on the opposite sides of thin plates has been established. From the displacement in the etch patterns on the two sides of thin plates, the angle of inclination of dislocation lines has been determined to be about 10°. Intersecting rows of pits forming nodes at which three or four rows meet have been observed. The implications are discussed.