MOLECULAR-DYNAMICS SIMULATIONS OF YTTRIUM-STABILIZED ZIRCONIA

The electric conductivity of yttrium-stabilized zirconia exhibits a ma ximum 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 tr ansport mechanisms at the molecular level. This was investigated by th e molecular dynamics simulations method in the present study. The comp osition dependency of the electric conductivity was found to agree qua litatively with experimental data. The conductivity was found to depen d on the dopant Y3+ distribution. The O2--O2- radial distribution func tion showed that oxygen ions were displaced about 0.37 Angstrom toward s O2- vacancies. The radial distribution functions of cations showed t hat the local structural environment of Y3+ ions was more disordered t han that of the Zr4+ ions. Oxygen vacancies were found to be nearest n eighbours of Y3+ ions. The y(3+)-Y3+ neighbour clusters trapped more O 2- vacancies than did isolated Y3+ ions, and this tendency increased w ith 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.