First principles study of segregation to the Σ5(310) grain boundary of cubic zirconia

While yttrium and impurity segregation at interfaces of yttria-stabilized zirconia (YSZ) has been intensively studied experimentally, the mechanisms governing the propensity for segregation are still not fully understood. The segregation energetics of yttrium and aluminum, another common segregant at interfaces of YSZ, were studied by means of first principles calculations based on density functional theory. Site-dependent formation energies were calculated following the substitutional incorporation of yttrium and aluminum in the near-interface region of the Σ5(310) grain boundary in cubic zirconia, for which recent experimental data revealed strong yttrium enrichment. Aluminum segregation was found to be strongly favored, accompanied by extensive changes in its local environment and coordination. Yttrium displayed a segregation propensity dependent on the site of substitution that correlated with the ability of its surrounding environment to accommodate the misfit strain by a breathing-type relaxation and increase of the nearest-neighbor yttrium-oxygen distances. Formation energies of oxygen vacancies were also determined near the interface, both as isolated defects and also by considering cosegregation with yttrium; the ensuing defect association led to stable yttrium-vacancy complexes and increased the energy gain from yttrium incorporation at the core of the grain boundary.