Surface structures and defect properties of pure and doped La2NiO4

Computer modelling techniques are used to investigate the surface properties and defect chemistry of the La2NiO4 material. Relaxed surface structures and energies are calculated for the low index planes which are used to predict the equilibrium crystal morphology. The {111} surface is calculated to dominate in the absence of impurities, water or surface irregularities, with significant contributions from the {100} and {001} surfaces. Isovalent doping 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 predicted to create the {011} face which is not present in the undoped crystal. 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 correlated to the observed catalytic activity.