Formation of gamma-Fe2O3 nanoparticles and vacancy ordering: An in situ X-ray powder diffraction study

The formation of maghemite, gamma-Fe2O3 nanoparticles has been studied by in situ X-ray powder diffraction. The maghemite was formed by thermal decomposition of an amorphous precursor compound made by reacting lauric acid, CH3(CH2)(10)COOH with Fe(NO3)(3)center dot 9H(2)O. It has been shown that cubic gamma-Fe2O3 was formed directly from the amorphous precursor and that vacancy ordering starts about 45 min later at 305 degrees C resulting in a tripled unit cell along the c-axis. The kinetics of grain growth was found to obey a power law with growth exponents it equal to 0.136(6) and 0.103(5) at 305 and 340 degrees C, respectively. Particles with average sizes of 12 and 13 nm were obtained in 86 and 76 min at 305 and 340 degrees C, respectively. The structure of cubic and vacancy ordered phases of gamma-Fe2O3 was studied at 305 degrees C by Rietveld refinements. (c) 2006 Elsevier Inc. All rights reserved.