Oxide Ion Mobility in V- and P‑doped Bi₂O₃‑Based Solid Electrolytes: Combining Quasielastic Neutron Scattering with Ab Initio Molecular Dynamics

We report the direct observation of oxide ion dynamics on both nano- and picosecond timescales in the isostructural Bi2O3-derived solid electrolytes Bi0.852V0.148O1.648 and Bi0.852P0.148O1.648 using quasielastic neutron scattering. Comprehensive ab initio molecular dynamics simulations allowed us to reproduce the experimental picosecond timescale data by directly simulating the scattering function at various temperatures. Our analysis of the experimental data in conjunction with the simulations revealed the origin of the picosecond dynamics to be localized motions within the V–O and P–O sublattices, while nanosecond dynamics correspond to the diffusion of the oxide ions in the Bi–O sublattice via vacancy-hopping. This combined approach provides insight into the different oxide ion migration pathways and mechanisms in Bi0.852V0.148O1.648 and Bi0.852P0.148O1.648, with the flexibility of the V coordination environment playing an important role, consistent with the superior conductivity of the vanadate