Thermodynamic description of the K, Be//F, Cl salt system with first-principles calculations

Abstract

Reciprocal molten halides are a distinctive class of high-temperature ionic liquids used as thermal and electrolytic media in the respective fields of MSR (molten salt nuclear reactor) and metallurgy. Strong Short-Range Ordering (SRO) from both the first-nearest (cation-anion) and second-nearest (cation-cation and anion-anion) neighbors defy accurate theoretical simulations of their physical and chemical properties and hence impede quantitative designs of optimum media applicable to industrial sectors. Based upon the Modified Quasichemical Model in the Quadruplet Approximation (MQMQA) coupled with the Multi-State Model (MSM), we developed a model (K+, BeIV2+, Be24+//F−, Cl−) to describe the thermodynamic behavior of the complex reciprocal K, Be//F, Cl liquid, where various types of SRO were evidenced by theoretical and experimental observations. This combinatorial method can quantitatively generate various sorts of quadruplets, thus providing structural entities to build other thermo-physical models. The thermodynamic properties of solid salts were also investigated to be able to calculate the entire reciprocal phase diagram. A vast amount of DFT (Density Functional Theory)-based first-principles predictions was performed based on various combinations of Pseudopotentials and Exchange-Correlation Functionals, SQS (special quasi-random structure) models of solid solutions and data-mining screened crystal structures of double salts. The calculations are in satisfactory agreement with the available experimental data, thus showing that the simulation capability could promote industrial advancements through a quantitative design of innovative materials.