Proton conducting oxide materials
The focus of this project is the simulation of proton conductive materials, in particular BaZrO3, acceptor-doped BaZrMxO3H, and Ba2In2O5(H2O) oxides. The general aim is to unveil the microscopic mechanistic aspects of the proton dynamics, and to correlate atomic-scale motions to lattice dynamics, in the moderate temperature regime. We will perform ab initio molecular dynamics calculation on a set of phases while varying mainly stoichiometries and temperatures. Most calculations, i.e. energy calculation, geometry optimisation of local structures, as well as molecular dynamics, will be performed in the DFT framework as implemented in the VASP package. Molecular dynamics instead of ‘standard’ phonon calculations will allow us to simulate complex and heavily doped system, showing few to none symmetry operators. Structural models are based on our own results from neutron diffraction experiments, as well as structures reported in literature, and are expected to contain from about 150 to 350 atoms. On top of results directly extracted from molecular dynamics trajectories, such as diffusion pathways and local structure configurations, we aim to calculate vibrational densities of states (vDOS) using the velocity auto-correlation function, as well as the scattering function S(q,w) at specific high-symmetry Q-values available through the choice of the supercell. Classical MD simulations using available force fields will also be performed on larger systems and for substantially longer times. Calculated scattering functions will be used to prepare and analyse data from spectroscopic experiments, in particular from inelastic neutron scattering experiments on time-of-flight (TOF) and three-axis (TAS) spectrometers. Such a joint study between inelastic neutron scattering and ab initio molecular dynamics have proven its efficiency in related perovskite-based oxide ion conductors, and should provide important insights on microscopic mechanisms of proton conductivity in the moderate temperature regime in perovskite-based oxides, which is both of fundamental and practical interest for the design and material engineering of future proton conductors.