Guanidine aluminum sulfate hexahydrate — A new ferroelectric material

Guanidine aluminum sulfate hexahydrate is ferroelectric over a large range of temperatures including room temperature. It is the parent of a family of materials in which the aluminum cation and the sulfate anion can be replaced by the anions and trivalent cations which form alums, for example Ga³⁺, Cr³⁺, and SeO₄^-. Replacement of guanidine has so far proved impossible, The material is trigonal, with perfect cleavage in the basal plane; the trigonal axis is the ferroelectric direction. The space group is C_3v(2) - P3lm, and the unit cell contains three molecules. It can be readily grown from water solution by standard techniques.