The detection of the change in mean inner potential at dislocations in grain boundaries in NiO

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Abstract
An electron microscope imaging technique is described which is sensitive to the change in mean inner potential associated with the core region of dislocations in NiO. Through-focus series of end-on dislocations in grain boundaries in NiO imaged under kinematical conditions show characteristic contrast behaviour related to the presence of a change in mean inner potential. Theoretical contrast calculations confirmed that the image contrast is caused by a decrease in mean inner potential. The origin of this decrease could be a change in density at, a charge on, or local segregation at the dislocation core. By fitting the calculated images to the observations a semi-quantitative estimate can bo made of the decrease in mean inner potential. If this decrease is related entirely to the decrease in density, there is poor agreement v ith the predictions of theoretical models of the dislocation core structure in NiO.