title: Static and Dynamical Structural Investigations of Metal-Oxide Nanocrystals by Powder X-ray Diffraction: Colloidal Tungsten Oxide as a Case Study.
abstract: 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.
authors.affiliation: IC CNR-Institute of Crystallography, via Amendola, 122/o, Bari, 70126, Italy. rocco.caliandro@ic.cnr.it.
authors.forename: Rocco
authors.identifier: http://orcid.org/0000-0002-0368-4925
authors.initials: R
authors.lastname: Caliandro
authors.affiliation: IC CNR-Institute of Crystallography, via Amendola, 122/o, Bari, 70126, Italy.
authors.forename: Teresa
authors.initials: T
authors.lastname: Sibillano
authors.affiliation: IC CNR-Institute of Crystallography, via Amendola, 122/o, Bari, 70126, Italy.
authors.forename: B Danilo
authors.identifier: http://orcid.org/0000-0003-2880-1064
authors.initials: BD
authors.lastname: Belviso
authors.affiliation: Dipartimento di Matematica e Fisica "E. De Giorgi", Università del Salento, via Arnesano, Lecce, 73100, Italy.|Center for Biomolecular Nanotechnologies@UNILE, Istituto Italiano di Tecnologia, via Barsanti, Arnesano, (LE), 73010, Italy.|CNR NANOTEC-Institute of Nanotechnology c/o Campus Ecotekne, University of Salento, via Monteroni, 73100, Lecce, Italy.
authors.forename: Riccardo
authors.identifier: http://orcid.org/0000-0002-6277-1252
authors.initials: R
authors.lastname: Scarfiello
authors.affiliation: Chemistry Department, Brookhaven National Laboratory, P.O. Box 5000, Upton, NY, 11973-5000, USA.
authors.forename: Jonathan C
authors.identifier: http://orcid.org/0000-0003-0686-3985
authors.initials: JC
authors.lastname: Hanson
authors.affiliation: Photon Sciences, Brookhaven National Laboratory, P.O. Box 5000, Upton, NY, 11973-5000, USA.
authors.forename: Eric
authors.initials: E
authors.lastname: Dooryhee
authors.affiliation: Center for Biomolecular Nanotechnologies@UNILE, Istituto Italiano di Tecnologia, via Barsanti, Arnesano, (LE), 73010, Italy.
authors.forename: Michele
authors.identifier: http://orcid.org/0000-0002-6903-2954
authors.initials: M
authors.lastname: Manca
authors.affiliation: Dipartimento di Matematica e Fisica "E. De Giorgi", Università del Salento, via Arnesano, Lecce, 73100, Italy.|CNR NANOTEC-Institute of Nanotechnology c/o Campus Ecotekne, University of Salento, via Monteroni, 73100, Lecce, Italy.
authors.forename: P Davide
authors.identifier: http://orcid.org/0000-0001-8037-6937
authors.initials: PD
authors.lastname: Cozzoli
authors.affiliation: IC CNR-Institute of Crystallography, via Amendola, 122/o, Bari, 70126, Italy. cinzia.giannini@ic.cnr.it.
authors.forename: Cinzia
authors.identifier: http://orcid.org/0000-0003-0983-2885
authors.initials: C
authors.lastname: Giannini
keywords: X-ray diffraction; colloids; nanoparticles; oxides; pair distribution function