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

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 ith the predictions of theoretical models of the dislocation core structure in NiO.