Molecular Dynamics Simulation of the Fast Ion Conductor δ-Bi₂o₃

Abstract

Molecular Dynamics simulations of the superionic δ-phase of Bi₂O₃ are reported. Initial configurations were based on 100,000 time-step (Δt = 5 × 10⁻¹⁵s) equilibrations. Making use of recently determined thermal expansivity data on δ-Bi₂O₃, a series of simulations were performed at increasing temperatures, with appropriate lattice constants, until oxygen sub-lattice melting was observed. Calculations were restricted to the rigid-ion approximation and accordingly short-range potentials, adjusted to reproduce the static dielectric constant were employed, in addition to modified electron-gas potentials. The dielectrically adjusted potentials proved superior in most respects although they sometimes prompted phase changes. In agreement with static-lattice calculation predictions the primary charge migration mechanism is a cube-edge or <<100>> vacancy migration. Cube-edge interstitials, half way along a cube-edge, predicted in static-lattice simulations and observed in neutron studies on yttria stabilized fluorite Bi₂O₃, are also found.

Key Words:

• Bismuth oxide
• bismuth sesquioxide
• fluorite
• molecular dynamics
• fast ion conduction