Far infrared transmission spectra of ferroelectric guanidine aluminium sulfate hexahydrate

Far IR transmission spectra of ferroelectric GASH are obtained at 300 K-80 K and 4 K for crystal plates cut perpendicular to C₃ with increasing thicknesses.Beer's law is well observed from t=20 m to t=55 m, which shows that such samples are homogeneous. For t=700 m the computed absorption is higher than observed, and a surface layer model is proposed where the bulk is more transparent than the surface.Similar effects have been observed in TGS where even for t=8 mm thick samples, the transmission of the lowest frequency band does not go to zero. A similar experiment is planned for GASH before making any definite conclusion on the evidence of surface layers in GASH.