Static and Dynamical Structural Investigations of Metal-Oxide Nanocrystals by Powder X-ray Diffraction: Colloidal Tungsten Oxide as a Case Study

• Published in: Chemphyschem 2016-03, Vol.17 (5), p.699-709
• Main Authors: Caliandro, Rocco, Sibillano, Teresa, Belviso, B. Danilo, Scarfiello, Riccardo, Hanson, Jonathan C., Dooryhee, Eric, Manca, Michele, Cozzoli, P. Davide, Giannini, Cinzia
• Format: Article
• Language: English
• Subjects: colloids; Crystal structure; Diffraction; function; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; MATERIALS SCIENCE; Multivariate analysis; nanoparticles; NANOSCIENCE AND NANOTECHNOLOGY; oxides; pair distribution; pair distribution function; X-ray diffraction
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.201501175

We have developed a general X‐ray powder diffraction (XPD) methodology for the simultaneous structural and compositional characterization of inorganic nanomaterials. The approach is validated on colloidal tungsten oxide nanocrystals (WO3−x NCs), as a model polymorphic nanoscale material system. Rod‐shaped WO3‐x NCs with different crystal structure and stoichiometry are comparatively investigated under an inert atmosphere and after prolonged air exposure. An initial structural model for the as‐synthesized NCs is preliminarily identified by means of Rietveld analysis against several reference crystal phases, followed by atomic pair distribution function (PDF) refinement of the best‐matching candidates (static analysis). Subtle stoichiometry deviations from the corresponding bulk standards are revealed. NCs exposed to air at room temperature are monitored by XPD measurements at scheduled time intervals. The static PDF analysis is complemented with an investigation into the evolution of the WO3−x NC structure, performed by applying the modulation enhanced diffraction technique to the whole time series of XPD profiles (dynamical analysis). Prolonged contact with ambient air is found to cause an appreciable increase in the static disorder of the O atoms in the WO3−x NC lattice, rather than a variation in stoichiometry. The time behavior of such structural change is identified on the basis of multivariate analysis. Static and dynamical structures: The crystal phases of colloidal tungsten oxide nanorods synthesized by non‐hydrolytic routes under oxygen‐free conditions are identified by static X‐ray diffraction analysis. The impact of prolonged air exposure on the structural properties are revealed by applying the modulated enhanced diffraction technique to repeated pair distribution function measurements.