Molecular dynamics simulations of point/line defect structures and oxygen diffusion mechanism in yttrium-doped barium zirconate

Abstract

Yttrium-doped barium zirconate is one of the most attractive electrolyte candidates for solid oxide fuel cells due to its excellent chemical stability and ionic conductivity. For the first time, this paper studies the barium zirconate systems coexisting point defects and line defects by classical molecular dynamics simulations in combination with the Coulomb-Buckingham potential, and the influences of yttrium dopants and oxygen vacancies concentrations and the edge dislocations on the structures and oxygen transport properties. The calculated results have shown that the diffusion coefficient is related to concentration of dopant, and it is not conducive to oxygen conduction when the dopant concentration is too high or too low. And it is concluded that 30% Y-doped barium zirconates have the highest diffusion coefficients regardless of the presence of edge dislocation defects. In addition, at the temperature of 1073.15 K, the diffusion of oxygen ion has been accelerated by edge dislocations when the dopant concentration is less than 30%, which could be explained by the gathering-jogging transport mechanism among edge dislocation, oxygen vacancy and oxygen ion. Therefore, the dopant concentration of barium zirconate should not be too high in practical applications of solid electrolytes, and it is feasible to introduce line defects to enhance ion conductivity.