Thermal line broadening of totally symmetric vibrations in the Raman scattering spectra of LiNO3–LiClO4, Na2CO3–Na2SO4, and KNO3–KNO2 binary systems

Abstract

The molecular relaxation processes in the solid binary systems of LiNO3–LiClO4, Na2CO3–Na2SO4, and KNO3–KNO2 were studied by Raman spectroscopy. It was found that the relaxation times of the ν1(A) vibrations of the NO3− and CO32− anions in the LiNO3–LiClO4, Na2CO3–Na2SO4, and KNO3–KNO2 systems are less than those in LiNO3, Na2CO3, and KNO3, respectively. It is shown that the increase in the relaxation rate is explained by the presence of an additional relaxation mechanism of vibrationally excited states in the system. This mechanism is associated with the excitation of a vibration of another anion (ClO4−, SO42−, NO2−) and the creation of a lattice phonon. It is established that the conditions for the realization of such a relaxation mechanism are that the frequency difference of these vibrations must correspond to a region with a sufficiently high density of states in the phonon spectrum.