The microstructure of ZnO powder, obtained from thermal decomposition of the oxalate and studied previously by electron microscopy and adsorption calorimetry, was investigated by means of X-ray powder diffraction pattern decomposition. A WilliamsonHall plot revealed that some lines were broadened solely due to the effects of crystallite size, whereas other breadths included a contribution due to stacking faults. Spherical and cylindrical models are used to describe the form of the crystallites and procedures are presented for separating 'size' effects from 'mistake' broadening. This leads to estimates of the mean dimensions of the crystallites and the stacking-fault probability. The analysis demonstrates that, with good-quality data for a large number of reflections, a considerable amount of detailed information can be obtained about microstructure. On the other hand, it reveals some of the limitations of current procedures for modelling diffraction line profiles.

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.

The Fourier and variance methods are used to analyse the breadths of X-ray diffraction peaks from ZnO powder obtained from the thermal decomposition of Zn3(OH)4(NO3) 2. The shape, size, distribution of size and orientation of the crystallites are determined. It is found that the form is markedly anisotropic and that on average the crystallites may be regarded as cylinders with a diameter of about 110/~ and height about 240 A, but that they are in fact right prisms whose cross section is an irregular hexagon. There is excellent agreement between the experimental results and the predictions of line-broadening theory, with quantitative confirmation from electron micrographs of the sample.

A detailed analysis of the microstructural properties of nanocrystalline cerium(IV) oxide powders produced by thermal dehydration of two hydrated ceria precipitated from the ceric ammonium and sulfate salts in ammonia solutions is described. In addition, it is shown that the diffraction pattern of hydrated ceria can be modeled with the structure data of CeO 2 and that the average crystallite size for the precursor CeO 2 ‚1.6H 2 O is 19 Å. The analysis of nanocrystalline CeO 2 is based on the modern developments of X-ray powder diffraction line broadening analysis, using 16 Bragg reflections. It is shown that, on average, the crystallites have a spherical shape with volume-weighted and area-weighted diameters in the ranges 264-1349 Å and 178-1079 Å for CeO 2 (am-CeO 2 ) obtained from the ammoniumbased ceria and 263-1756 Å and 195-927 Å for CeO 2 (sul-CeO 2 ) obtained from the sulfatebased ceria. The early stages of the crystallite growth have been studied up to 775 °C and 900 °C, respectively. While sul-CeO 2 is strain-free over the temperature range investigated, am-CeO 2 contains a small amount of strains decreasing with temperature until 700 °C, where strains are negligible. The kinetics of the crystallite growth has been studied for the two samples, from which activation energies have been calculated. Crystallite sizes are also compared to the values from SEM and BET measurements. Strain-free sul-CeO 2 is suggested as a potential candidate as reference material for crystallite size in powder diffraction.