X-ray diffraction and micro-Raman spectroscopy analysis of new nickel hydroxide obtained by electrodialysis

Industrial nickel hydroxide samples produced by electrodialysis have been characterized both by X-ray diffraction (XRD) and by micro-Raman spectroscopy. A comparison with some commercial products of β-type Ni(OH)2 is made. Aged in KOH solution, these nickel hydroxides are transformed to the β-Ni(OH)2 phase and undergo Ostwald ripening, leading to crystallite sizes ranging between 260 and 380 Å with a reduction in defects. The anisotropic broadening of the XRD peaks in the β-Ni(OH)2 pattern is interpreted in terms of crystalline lattice micro-strains and crystallite size. For the first time, Rietveld refinement has been performed on industrial Ni(OH)2. The results indicate that the micro-strain effects increase the peak width according to the sequence of families (hk0)→(00l)→(h0l). This study shows that the presence of proton vacancies leads to a lower degree of distortion in the crystalline lattice than does the presence of stacking faults or the adsorption of inorganic species at the border of the crystallites. A very high concentration of point defects inducing strong distortions in the crystal lattice is correlated with the presence of high energy Ni–O bond vibrations in the Raman spectra, with a frequency shift towards unusually high values.