Structural and microstructural characterization of Co-hydrotalcite-like compounds by X-ray diffraction

Co-hydrotalcite-like compounds (Co-HTlcs) were synthesized by coprecipitation technique from Mg(NO₃)₂·6H₂O, Al(NO₃)₃·9H₂O and Co(NO₃)₂·6H₂O, with a constant molar ratio Mg/Al of 1.6 and a variable molar ratio Co/Mg from 0.01 to 0.1 (controlling the pH around 10). X-ray diffraction was used to evaluate structural (lattice parameters) and microstructural (crystallite size and microstrain) parameters of the samples. Lattice parameters were calculated from (0 0 3), (0 0 6), (1 1 0) and (1 1 3) reflections by the least squares method, changes on a and c lattice parameters are discussed and related to Co/Mg ratio. The microstructural parameters were analyzed using two approaches: (a) analytical methods with the Voigt method and the two stages approach and (b) graphical methods using a modified Williamson-Hall plot with Lorentzian, Gaussian and Lorentzian-Gaussian variants. It was found that increasing the Co content, the morphology of crystallites tends to be plate-like and it was observed that the crystallite size increases, while the microstrain values decrease. This behavior is related to an improvement of crystal perfection, due to addition of cobalt.