Molecular dynamics simulation of the Ba1−xGdxF2+x system in a wide temperature range

Internal energy, diffusion coefficients, ion–ion correlation functions, anion density and characteristics of ionic motion in barium gadolinium fluoride (Ba1−xGdxF2+x, 0<x≤0.25) were calculated using molecular dynamics simulation. The simulations were performed for a wide range of temperatures, including the temperature of the superionic transition. The simple model interaction potential (Born–Mayer–Huggins model) was used. The calculated thermodynamic and transport properties are in satisfactory agreement with experiment; the discrepancies can be explained by the fact that cluster formation, which occurs in the real crystal, is not taken into account in the simulations. It was found that at x>0.1, both 4b and 48i positions in the lattice were relatively favorable for interstitial F− ions. At low dopant concentrations, anion migration in the simulated system takes place mainly by the interstitialcy mechanism with noncollinear hops. The computer experiment confirmed that trigonal Gd3+–F− (interstitial) “dipole complexes” are preferable in comparison with tetragonal ones. Existence of the tendency to clustering of gadolinium ions in the simulated system was also confirmed using elements of Monte Carlo technique.