Defect chemistry and surface properties of LaCoO3

Atomistic computer simulation techniques are used to investigate the surfac e properties and defect chemistry of the LaCoO3 perovskite. The theoretical techniques are based upon efficient energy minimisation routines, a 'two-r egion' strategy and the Mott-Littleton methodology for the accurate modelli ng 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. Char ge compensation is predicted to occur via oxygen ion vacancies which are be lieved to be key sites with regard to catalytic activity. Relaxed surface e nergies are calculated for the low index surfaces and the order of stabilit y is found to be {110} > {100} > {111}. The equilibrium morphology of LaCoO 3 is predicted from the surface energies, in which the {110} surface is cal culated to dominate in the absence of impurities or surface irregularities, with a lesser contribution from the {100} surface. The surface defect ener gies 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.