Numerical analysis of solute segregation at Σ5 (310) [001] symmetric tilt grain boundaries in Y2O3-doped ZrO2

Atomistic mechanisms that determine atomic coordination and local concentration of dopants at Σ5 (310) [001] symmetric tilt grain boundaries in Y2O3-doped ZrO2 are analyzed using atomistic simulation techniques. Segregation mechanisms are found to be different from those in metals or metalloids, with local strain relief controlled by short-range interactions, which act as the driving force for segregation, while long-range Coulombic interactions between the grain boundary region and the dopants resist segregation. It is found that Y3+ ions segregate to a region within around 0.6 nm either side of the grain boundary plane. The equilibrium local concentration of dopants in the vicinity of the grain boundary, which is determined by the balance between repulsive forces between dopants and the grain boundary and attractive forces associated with local strain relief, is calculated to be 16.7 mol% for 10.3 mol% Y2O3-doped ZrO2. Cosegregation of an O2- vacancy is necessary to accommodate a Y3+ ion at the Σ5 grain boundary; O2- vacancies play important roles in reducing repulsion between dopants and the grain boundary and relieving local strain further. These conclusions are supported by Monte Carlo simulations using an unrestricted model. Segregation-induced modifications to the grain boundary structure observed in the simulations are used to interpret experimental HREM and Z-contrast images.