Ionic conductivity of molten alkali-metal carbonates ACO (A = Li, Na, K, Rb, and Cs) and binary mixtures (LiCs)CO and (LiK)CO: A molecular dynamics simulation.

Based on experimental data, we optimized the potential parameters for the classical molecular dynamics simulation to reproduce the volume and ionic conductivity of the molten alkali-metal carbonates ACO where A = Li, Na, K, Rb, and Cs at T/K = 1223 and ambient pressure. The force field was then applied to the binary mixtures (LiCs)CO and (LiK)CO. In (LiCs)CO, the diffusion coefficient D exceeds D at x > 0.6, testifying to the Chemla effect. The net ionic conductivity was broken down into the contributions from the velocity auto- and cross-correlations of each ionic species. The significant negative deviation of the real conductivity of (LiCs)CO from the one estimated by the Nernst-Einstein (NE) relation is clearly explained by the contribution from the cross correlations; specifically, the cross term between Liand CO , which is negative at x = 0, significantly shifts to the positive side when x increases, which is dominantly responsible for dampening the conductivity from the NE conductivity. A similar behavior was observed in (LiK)CO with a less pronounced manner than in (LiCs)CO. These observations corroborate the precedent studies pointing to the trapping of Li by the anion when a lithium salt is mixed with another salt of which the cation size is greater than that of Li.