Can the ionicity of sapphire be determined using HREM?

摘要

The imaging behaviour of sapphire is investigated at a range of resolutions using both neutral and ionic scattering factors for aluminium and oxygen as well as scattering factors of exemplary intermediate character. The relative behaviour of reflections associated with difference and addition effects for the two constituents is shown to be of particular interest given the way a fully ionic character makes the forward scattering behaviour for the respective ions almost identical. This in turn leads to strong effects of ionicity on the imaging behaviour out to otherwise surprising resolutions.