Structural characterization of nanocrystalline CrOOH·2H 2O aerogel by X-ray diffraction

A. Erenburg, E. Gartstein, M. Landau

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Abstract

The nanostructured powder prepared by critical CO2 extraction of the urea-assisted wet chromia gel mixture at 373 K in vacuum was studied by X-ray diffraction techniques. Thermoanalytical methods showed the presence of the lattice water molecules in the resulting phase corresponding to a chemical formula CrOOH · 2H2O. The CrOOH · 2H2O nanocrystals of 3-5 nm in diameter were observed in transmission electron microscopy and their structure was derived from the Rietveld analysis in which the disorder contribution to the X-ray scattering was implemented. The structural model shows that the hexagonal unit cell of α-CrOOH undergoes monoclinic distortion with half of the O-2 anions and OH- groups being replaced by bonded water molecules in the three-dimensional packing resulting in half of the sites in regular Cr+3 octahedra being vacant. Further examination of the quasi-crystalline disordered state of the CrOOH·2(H2O) nanocrystals was performed by model independent method of Radial Distribution Function (RDF). This complementary technique is sensitive to the molecular composition and allows to assess the average atomic (or electron) density distribution and the spacings of the atomic arrangements in the nearest neighbor shells comprising the range of the crystalline order in the structure of this material.

Original languageEnglish
Pages (from-to)81-90
Number of pages10
JournalJournal of Physics and Chemistry of Solids
Volume66
Issue number1
DOIs
StatePublished - 1 Jan 2005

Keywords

  • A. Nanostructures
  • B. Sol-gel growth
  • C. X-ray diffraction
  • D. Crystal structure

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