X-ray Diffraction Study of the Early Stages of the Growth of Nanoscale Zinc Oxide Crystallites Obtained from Thermal Decomposition of Four Precursors. General Concepts on Precursor-Dependent Microstructural Properties

A detailed analysis of the microstructural properties of nanocrystalline zinc oxide powders produced by thermal decomposition of four different precursors (hydroxide nitrate, oxalate, hydroxide carbonate, and acetate) is described. The analysis is based on the modern developments of X-ray powder diffraction line broadening analysis. The early stages of the crystallite growth up to 600 °C have been studied in situ at constant heating rate and ex situ from samples prepared under isothermal conditions. It is shown that the crystallites are prismatic and can be averaged by a cylindrical shape with diameter D and height H . The thermal behavior of crystallite size and shape aspects depends on the nature of the precursor. Above ∼350 °C, the constant value of D/H demonstrates that similar crystallite shapes are observed during crystallite growth. The kinetics of the crystallite growth has been studied for the four samples, from which activation energies have been calculated. Crystallite sizes are also compared to values from SEM and BET measurements. The agglomeration process of the crystallites is investigated from a comparison between surface areas calculated from the BET method and the powder diffraction analysis. From the complete results, general rules on the precursor dependence of the observed microstructural properties are established.