A simple tight-binding model of vacancies in SnO2 crystalline grains

The properties of defective SnO2 crystalline grains have been evaluated quantum-mechanically using a tight-binding total-energy formulation with a rigid-lattice model. The shape of the grains is constructed on the basis of known features of the nanocrystalline material and the grain size is comparable with those observed in experiments. The grains have a rutile lattice and the presence of vacancies in one or other of the two sublattices is accounted for. The calculations indicate that, owing to the peculiar connectivity of the grains, the effect of a vacancy is critical and alters the stability of bonding even when the defect concentration is minimal.