Structure of molten nitrates. V. Effect of cation change and anion symmetry on melt structure

Abstract

A previous study of the effect of univalent cations on the intensity of symmetrical stretching frequency in nitrate melts has been extended. The use of divalent cations Mg²⁺, Ca²⁺, Pb^2-, and Cd²⁺ has confirmed that for systems in which covalent bonding is not important the intensity of the symmetrical stretching frequency decreases linearly with the strength of the cationic field. In systems for which covalent interactions are important the change in intensity is probably related to the electronic structure of the cation. The low frequency vibrational modes for the melts studied also showed great variation in intensity. This has been correlated with the variation in the anisotropy of the anionic polarizability and substitution in the pseudo lattice of the melt. The effect of the anisotropy of the polarizability was further studied by replacing the nitrate ion by perchlorate, chlorate, and nitrite. The measurements showed that the greater the anisotropy the higher the intensity of the lattice modes.