Surface structures and defect properties of pure and doped La2NiO4

Computer modelling techniques are used to investigate the surface propertie s and defect chemistry of the La2NiO4 material. Relaxed surface structures and energies are calculated for the low index planes which are used to pred ict the equilibrium crystal morphology. The {111} surface is calculated to dominate in the absence of impurities, water or surface irregularities, wit h significant contributions from the {100} and {001} surfaces. Isovalent do ping of the Ni site by Fe and Cu is found to affect the crystal morphology by increasing the expression of the {001} surface, although Fe doping is pr edicted to create the {011} face which is not present in the undoped crysta l. The Sr dopant at the La site is calculated to be the most soluble of the alkaline earth metals, in accord with observation. Charge compensation is predicted to occur via the formation of Ni( III), which is consistent with bulk calculations and catalytic models in which Ni( III) species are correl ated to the observed catalytic activity.