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Computer modelling techniques are used to investigate the surface properties and defect chemistry of the La 2 NiO 4 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.

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Solid‐state optical materials are a continuing field of study that has many important applications including lasers. YLiF4 is one material has been studied in detail however, no studies into the surface properties or crystal morphology have been carried out. This paper summaries the key findings of a bulk study into the material and extends it to consider the morphology of pure YLiF4 before looking at the segregation of rare earth dopants to the low index surfaces. The presence of these dopants at the surfaces is shown to have a stabilising effect on some of the indices resulting in a lowering of the surface energy. By considering the optimum dopant coverage at all surfaces, a prediction for the doped La:YLiF4 crystal is made. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)