Dislocation-Pipe Diffusion of Protons in Hydrated Yttrium-Doped Barium Zirconate Simulated by Reactive Molecular Dynamics

Yttrium-doped barium zirconate (BZY) electrolyte is receiving more and more attention due to the dual migration ability of protons and oxygen ions. Herein, reactive molecular dynamics simulations are carried out to investigate the defect structures and ion transport mechanism of BZY coexisting protons, oxygen vacancies, and edge dislocations, and the effects of dopant concentration and temperature on structural and kinetic properties are also considered. It is shown that the slightly elongated O–O distance of the fully hydrated bulk system (Bulk HY) facilitates the dynamics of host oxygen sublattices, thereby promoting proton hopping. Besides, the lowest activation energy of protons diffusion for a fully hydrated dislocation system (Disl HY) is attributed to the weak association between dopants and protons, and similar pre-exponential factors of Disl HY and the partially hydrated dislocation system (Disl VHY) are related to the oxygen dynamics. It is concluded that the dopant concentration of 20% for Bulk HY is optimal for proton conduction, and the proton concentration is a key factor affecting overall conductivity by comparing Disl HY with Disl VHY. Ultimately, the long-range dislocation-pipe diffusion of protons in Disl HY is revealed from the motion trajectories and possibility distributions of protons, and the trapping-hopping mechanism is put forward to elaborate the role of oxygen vacancy on proton conduction.