A RAMAN SPECTROSCOPIC INVESTIGATION OF COPPER-CHLORINE BORACITE
Cu-Cl boracite occurs in an anhydrous and a hydrated form. The possible differences between them and the dynamics of the phase transition are of interest. The spectra of anhydrous and hydrated Cu-Cl boracite are studied using laser Raman spectroscopy at different temperatures in the vicinity of the phase transition temperature. The number and symmetry of Raman active modes is calculated for the orthorhombic and cubic phase of boracite using factor group analysis. The spectra of the anhydrous and hydrated CuCl boracite are shown to be different proving that there are physical differences between the two crystals more fundamental than the difference in color. A mathematical model of the data based on fluctuation dissipation theory is utilized for analyzing the spectra. Two soft modes are discovered and the analysis gives the variation of their frequency with temperature. The frequency variation of the modes is related to the temperature variation of the low frequency dielectric constant by means of the Lyddane-Sachs-Teller relation. The frequencies of the modes are shown to be indirectly coupled to the phase transition mechanisms which is predicted for an improper ferroelectric such as boracite. It is shown that the variation in intensity of the low frequency scattering is inconsistent with both a soft mode model and an overdamped soft mode model. The data is consistent with an anharmonic phonon interaction theory.
FLAHERTY, FRANCIS A, "A RAMAN SPECTROSCOPIC INVESTIGATION OF COPPER-CHLORINE BORACITE" (1983). ETD Collection for Fordham University. AAI8323523.