Molecular dynamics simulations of yttrium-stabilized zirconia

The electric conductivity of yttrium-stabilized zirconia exhibits a maximum as a function of dopant (Y³⁺) cation concentration in isothermal and isobaric conditions. In order to improve the conductivity of this important solid electrolyte, it is essential to understand the ion transport mechanisms at the molecular level. This was investigated by the molecular dynamics simulations method in the present study. The composition dependency of the electric conductivity was found to agree qualitatively with experimental data. The conductivity was found to depend on the dopant Y³⁺ distribution. The O²-O^2- radial distribution function showed that oxygen ions were displaced about 0.37 AA towards O^2- vacancies. The radial distribution functions of cations showed that the local structural environment of Y³⁺ ions was more disordered than that of the Zr⁴⁺ ions. Oxygen vacancies were found to be nearest neighbours of Y³⁺ ions. The Y³⁺-Y³⁺ neighbour clusters trapped more O^2- vacancies than did isolated Y³⁺ ions, and this tendency increased with increasing Y₂O₃ concentration in ZrO₂ because more and larger Y³⁺-Y³⁺ clusters were formed. We suggest that this is responsible for the observed isothermal conductivity decrease at high Y₂O₃ contents in the yttrium-stabilized zirconia.