Analytical Electron Microscopy Study of a ZnO-NiO Solid Solution

Abstract.

 Results of an analytical electron microscopy study of a binary ZnO-NiO system are reported and discussed. Emphasis was placed on the determination of Ni concentration (solubility) in the ZnO grains using quantitative TEM-EDXS. The influence on the results of beam diameter, foil thickness and corrections used are described and discussed. During the study small precipitates, presumably NiO, were found in the ZnO grains of the ZnO-NiO samples with different ZnO/NiO ratios. In TEM, the precipitates exhibited image contrast only at certain orientations and were normally invisible during the EDXS analysis. The presence of the precipitates too small to be seen using scanning electron microscopy could explain erroneous results for the Ni concentration in a ZnO solid-solution phase obtained previously using SEM-EDXS. Quantitative EDXS analyses were performed on ZnO grains using different electron beam diameters. In each sample, the spread of the results was correlated to the beam diameter (analysed volume). It was found that when the average number of precipitates was less than one per analysed volume the measured points that included precipitates could easily be identified on the basis of their deviation from the mean value of the Ni content.