Spiral Patterns on Cleavage Surfaces of Ferroelectric Guanidinium Aluminum Sulfate Hexahydrate

Spiral patterns due to screw dislocation have been revealed by a charged-powder deposition technique on cleavage surfaces in {0001} growth region of ferroelectric guanidinium aluminum sulfate hexahydrate crystals grown from aqueous solution of high temperatures (60°C–95°C). The patterns are observed not as surface topography on the natural faces of crystal, but as charge distribution on the cleavage surfaces in the crystal. Dislocation etch pits found at the center of the spirals are direct evidence for the spiral growth of crystal along the trigonal axis. The rotational motion of the spiral patterns during crystal growth is discussed on the basis of the spiral growth theory.