First-Principles Descriptors of Heteroanion Effects on Early-Stage Ni Segregation in SrTiO3

Exsolution of Ni nanoparticles from SrTiO3-based perovskites is a promising route to thermally stable solid oxide fuel cell anodes. A-site deficiency and B-site cation substitution are widely used to promote exsolution, but the effect of heteroanionic substitution in the oxygen sublattice remains less well understood. Here, we use first-principles density functional theory to examine how N, S, F, and Cl substitution modifies descriptors associated with early-stage Ni surface segregation energetics in a SrTiO3-derived model. The calculations show that heteroanion substitution alters Ni segregation by changing local lattice distortion, defect electrostatics, Ni–anion bonding, oxygen-vacancy formation, migration barriers, and electronic structure. However, each calculation is restricted by its probing intentions and the models used. Within the model set, F gives the most favorable O-site substitution formation energy in the bulk model and Ni segregation energy at the surface site. N gives the most favorable Ni segregation energy in the bulk site and oxygen-vacancy formation energy at the selected site. Cl gives the lowest barrier along the sampled Ni-migration pathway, and S gives the smallest computed Kohn–Sham gap, which does not reflect enhanced conductivity. Rather than identifying a single optimal dopant, these results reveal how different heteroanions tune distinct descriptors relevant to early-stage Ni segregation. The descriptor set provides a comparative theoretical basis for using oxygen-sublattice chemistry to guide the design of heteroanionic SrTiO3-based anodes.