Ferroelectric Moment in Guanidinium Aluminum Sulfate Hexahydrate, GASH

Examination of the details of the crystal structure of the isomorphous compounds GASH and GCrSH has lead to the recognition of a possible mechanism for the ferroelectric reversal of polarization direction. The suggested mechanism predicts the possibility of the occurrence of ``pseudodomains,'' i.e., contiguous regions in the crystal having the same direction of polarization, but separated by ``pseudodomain walls.'' Calculation, from the structure parameters, of the magnitude of the ferroelectric dipole for the two crystals gives satisfactory agreement with the experimental values. Preliminary measurements of x-ray diffraction intensities with CuKα radiation on poled crystals of GCrSH are in accord with the proposed model.