Isotropic and anisotropic Raman scattering from molten LiCl–CsCl mixtures: Composition and temperature effects

Abstract

Molten mixtures of lithium chloride and cesium chloride have been studied using Raman spectroscopy at temperatures up to 850 °C. Reduced isotropic and anisotropic Raman relative intensities have been measured at different compositions and temperatures. The spectra of the mixtures show two bands with ‘‘characteristic’’ frequencies ωCs and ωLi close to the frequencies of the bands of the pure components. Both ωCs and ωLi shift to higher energies with increasing mole fraction of CsCl and LiCl, respectively. The scattering intensity spectra of the mixtures are compared with the simulated additive spectra of the component salts. Increasing temperature increases drastically the isotropic intensity of the ωLi band but has minor effects on the anisotropic intensities. The data are discussed and interpreted in terms of interaction-induced polarizability fluctuations. Short range overlap interactions, mainly between Li+ and Cl−, and the ‘‘symmetry’’ of the local structure around the anion determine the breathing-like fluctuations which contribute to isotropic scattering and account for the drastic temperature and composition dependence of the Raman intensities. The main contribution to anisotropic scattering arises from near-neighbor dipole-induced-dipole interactions between the highly polarized Cs+ and Cl− ions.