Molecular dynamics investigations of grain boundary phenomena in cubic zirconia

Yttria stabilized zirconia (YSZ) is a fast oxide ion conducting ceramic with the cubic fluorite structure that is used in a number of applications, including solid oxide fuel cells (SOFCs). A molecular dynamics (MD) study has been performed on symmetrical tilt grain boundaries with the Σ5 (3 1 0)/[0 0 1] 0 = 36.9° misorientation to investigate the structure and dynamics of interfaces in this technologically important material. Simulations were performed on systems of 1920 atoms at constant temperatures up to 2673 K. Atomic interactions were described by a simple pair potential model of the Buckingham form. Structural relaxation produced an open structure corresponding to the introduction of a row of Schottky defects adjacent and parallel to the interface. Oxygen diffusion along the boundary was observed at high temperature, even without vacancies in the bulk being introduced explicitly by aliovalent doping. However, the diffusion rate was lower than that in single crystals of 8 mol% Y₂O₃ stabilized zirconia. Further simulations demonstrated that interfaces between perfect zirconia crystals are sources of resistance in these ionically conducting systems.