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--O2- radial distribution function showed that oxygen ions were displaced about 0.37 Angstrom towards O2- 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 y(3+)-Y3+ neighbour clusters trapped more O2- 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.