Defect chemistry and surface properties of LaCoO3

TLDR

Atomistic computer‑simulation methods, employing efficient energy minimisation, a two‑region strategy, and Mott–Littleton defect modelling, were used to study LaCoO3 surface properties and defect chemistry. Sr and Ca dopants are the most soluble alkaline‑earth elements, with charge compensation via oxygen vacancies; the calculated surface energies rank {110} > {100} > {111}, predicting a {110}-dominated equilibrium morphology, and lower surface defect energies drive dopant and vacancy segregation to the surface, boosting catalytic and electrochemical activity.

Abstract

Atomistic computer simulation techniques are used to investigate the surface properties and defect chemistry of the LaCoO3 perovskite. The theoretical techniques are based upon efficient energy minimisation routines, a ‘two-region’ strategy and the Mott–Littleton methodology for the accurate modelling of surface and bulk defects. Sr and Ca dopants are calculated to be the most soluble of the alkaline earth metals, in accord with observation. Charge compensation is predicted to occur via oxygen ion vacancies which are believed to be key sites with regard to catalytic activity. Relaxed surface energies are calculated for the low index surfaces and the order of stability is found to be {110} > {100} > {111}. The equilibrium morphology of LaCoO3 is predicted from the surface energies, in which the {110} surface is calculated to dominate in the absence of impurities or surface irregularities, with a lesser contribution from the {100} surface. The surface defect energies are generally lower than in the bulk crystal implying that the dopants and oxygen vacancies will segregate to the surfaces, thus enhancing their catalytic and electrochemical activity.