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

Abstract

We report the direct observation of oxide ion dynamics on both nano-and picosecond timescales in the isostructural Bi 2 O 3 -derived solid electrolytes Bi 0.852 V 0.148 O 1.648 and Bi 0.852 P 0.148 O 1.648 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 Bi 0.852 V 0.148 O 1.648 and Bi 0.852 P 0.148 O 1.648 , with the flexibility of the V coordination environment playing an important role, consistent with the superior conductivity of the vanadate.

Oxide Ion-Conducting Materials Containing Tetrahedral Moieties: Structures and Conduction Mechanisms

“…Meanwhile they employed variable-temperature quasielastic neutron scattering (VT-QENS) to understand the dynamics of oxide ion migration on the nanosecond time scale in Bi 0.913 V 0.087 O 1.587 composition, related to the highest oxide ion conductivity among the Bi 2 O 3 -based compositions. 221,222 The results demonstrated rapid motion dynamics between two nearest-neighbor oxygen sites with 2.83 Å distance during the heating progress and the nature of translational diffusion above 300 °C, which was ascribed to the rate-determining diffusion within the fluorite-like Bi−O substructures. Yet, the diffusion associated with VO n units is too fast to be detectable through the VT-QENS technique.…”

“…This accounts for the optimal oxide ion conductivity found in V-doped rather than P-doped materials, and more importantly highlights the significance of the variable coordination number of V to support the oxygen exchange. In addition, Peet et al and Schwaighofer et al performed long-scale AIMD simulations, which revealed that oxygen ion migration associated with M O n ( M = V and P) polyhedral substructures takes picoseconds, which is much faster than the nanosecond time scale for the Bi–O substructures (Figure ), meaning that oxygen migration in the Bi–O substructure is the rate-limiting step. Meanwhile they employed variable-temperature quasielastic neutron scattering (VT-QENS) to understand the dynamics of oxide ion migration on the nanosecond time scale in Bi 0.913 V 0.087 O 1.587 composition, related to the highest oxide ion conductivity among the Bi 2 O 3 -based compositions. , The results demonstrated rapid motion dynamics between two nearest-neighbor oxygen sites with 2.83 Å distance during the heating progress and the nature of translational diffusion above 300 °C, which was ascribed to the rate-determining diffusion within the fluorite-like Bi–O substructures.…”

“…(b) MSD curves for oxygen atoms initially in the O–V and O–P substructures in Bi 0.852 V 0.148 O 1.648 and Bi 0.852 P 0.148 O 1.648 . Reproduced with permission from ref . Copyright 2023 American Chemical Society.…”

“…This accounts for the optimal oxide ion conductivity found in Vdoped rather than P-doped materials, and more importantly highlights the significance of the variable coordination number of V to support the oxygen exchange. In addition, Peet et al 221 and Schwaighofer et al 222 performed long-scale AIMD simulations, which revealed that oxygen ion migration associated with MO n (M = V and P) polyhedral substructures takes picoseconds, which is much faster than the nanosecond time scale for the Bi−O substructures (Figure 29), meaning that oxygen migration in the Bi−O substructure is the rate-limiting step. Meanwhile they employed variable-temperature quasielastic neutron scattering (VT-QENS) to understand the dynamics of oxide ion migration on the nanosecond time scale in Bi 0.913 V 0.087 O 1.587 composition, related to the highest oxide ion conductivity among the Bi 2 O 3 -based compositions.…”

Computational Insights into Dion–Jacobson Type Oxide Ion Conductors

“…The challenge in this approach has traditionally been the computational cost related to the size of the simulation box, which can realistically be probed. Nevertheless, AIMD simulations have successfully been used to elucidate ionic conduction pathways and mechanisms in oxide ion conductors belonging to a number of different structural families, including fluorites, − apatites, , LAMOX, and perovskite-related − materials.…”