Lattice parameter, microstrains and non-stoichiometry in NiO. Comparison between mosaic microcrystals and quasi-perfect single microcrystals

Twelve samples of three kinds of highly divided nickel oxide, prepared from nickel hydroxide at low temperature, have been compared from the double point of view of mean lattice parameter variation (uniform strain) and lattice microstrains (non-uniform strain). These samples are black non-stoichiometric NiO with a mosaic texture, a green stoichiometric NiO with the same mosaic texture and black non-stoichiometric NiO made up of tiny quasi-perfect single crystals (monolithic NiO). The textures of the three kinds of oxides have been inferred from electron microscopy and diffraction and X-ray diffraction. Crystallite sizes and microstrain values have been obtained from X-ray line broadening analysis. Deviations from stoichiometry have been obtained from chemical analysis. Correlations between uniform strain, non-uniform strain, texture and stoichiometry have been researched. It appears from the comparison of the results that uniform and non-uniform strains are insensitive to the extent of deviation from stoichiometry. The non-uniform strain is mainly due to the mosaic texture of the grains. The uniform strain related to the mean lattice parameter variation appears to be related to the small crystallite size. These two aspects are related to the mechanism of the oxide formation from the hydroxide.