Computer Simulation of Rare-Earth Molybdate Crystals of the R5Mo3O16 Family: I. Diffusion and Microscopy of Ion Transport in Nd5Mo3O16+δ (0 ≤ δ ≤ 0.7)

The ion transport in Nd5Mo3O16+δ (0 ≤ δ ≤ 0.7) crystals was studied using the molecular dynamics method. It was shown that ion transport is possible in the molybdates at elevated temperatures (T > 800 K), caused by the transport of different types of oxygen ions located in different crystallographic positions. Noticeable diffusion is observed in samples with deviations from the stoichiometric composition: at 1500 K, the highest values of the diffusion coefficients for crystals with δ = 0.7 are DO ~ 1.4×10–6 cm2/s. Ion transport involves both oxygen anions in the main positions of types O1 (to a smaller extent) and O2, as well as additional (superstoichiometric) oxygen anions of the O3 type. The hopping mechanism is described by “jumps” over distances from ~1.5 to ~2.5 Å. O2-type ions can move by ~4–5 Å for a simulation time of 400–600 ps, while O3-type ions undergo translational movement with jumps through several intermediate positions with a total displacement of ~6 Å.