Effect of Mg2+ Cation on the Phase Behavior and Local Structure of the Li0.42K0.58NO3 Eutectic Melt: A Raman Spectroscopy and DSC Study

Abstract

A comprehensive investigation was carried out in his work of the structural, thermal, and dynamic properties of the (1 − x)(Li_0.42K_0.58NO₃)–xMg(NO₃)₂ (x = 0–0.5) multicomponent nitrate system using combined light scattering and differential scanning calorimetry. The symmetric mode ν₁(\({\text{A}}_{1}^{{{'}}}\)) of the nitrate ion \({\text{NO}}_{3}^{ - }\) was used as a structure-sensitive probe. It was found that the introduction of Mg(NO₃)₂ leads to a significant rearrangement of the phase behavior of the initial eutectic melt: at concentrations x ≥ 0.3, signs of glass formation and subsequent devitrification are observed, which are accompanied by exothermic effects during heating. Quantitative analysis of the parameters of the ν₁(\({\text{A}}_{1}^{{{'}}}\)) oscillational mode revealed an increase in the amplitude of frequency fluctuations and an acceleration of oscillatory dephasing with increasing magnesium nitrate content. In this case, the contribution of heterogeneous broadening becomes dominant for intermediate compositions, indicating an increase in the structural heterogeneity of the system. It is shown that the addition of Mg²⁺ induces a transition from a simple eutectic melt to a structurally complex system with pronounced local heterogeneity and slowed relaxation dynamics.