SPECTROSCOPIC STUDIES OF FERROELECTRIC METHYL AMMONIUM ALUMS (MASD, MASeD and MCrSD)

Abstract

The Ramon spectra of CH3NH3Al (SO4)2 12H20 (MASD), CH3NH3A1 (SeO4)2 12H20 (MASeD) and deuterated MASD and the iufraredspectra of MASD, MASeD, MCrSD [CH3NH3Cr(SO4)2-12H2O] and deuterated MASD at different temperatures have shown that the sulphate or the selenate ion does not undergo any uppreriable dislorti'on by the ferroelectric phaw transition.A comparison of the Raman spectra of MASD at 300°, 200' and 100°K has shown hot the v2(SO4)2 CH3 stretching and H2O stretching vibrations at 988, 2991 and 3380 cm-1 respectively appeur with enhanced intensity in the spectrum of the frrroelectric phase. The observation of new infrared bands in the region 2750- 000 cm'l and at about 500 cm-' respectively due to the stretching and iorsional vihrarions of the CH3NH3+ ion suggests that a rearrangement of the CH,NH, ion is probably the triggering mechanism as suggested by O'Reilly and Tsang from magnetic resonance studies of MASD.