title: Structural behavior of laser-irradiated γ-Fe2O3nanocrystals dispersed in porous silica matrix : γ-Fe2O3to α-Fe2O3phase transition and formation of ε-Fe2O3.
abstract: The effects of laser irradiation on γ-Fe2O34 ± 1 nm diameter maghemite nanocrystals synthesized by co-precipitation and dispersed into an amorphous silica matrix by sol-gel methods have been investigated as function of iron oxide mass fraction. The structural properties of γ-Fe2O3phase were carefully examined by X-ray diffraction and transmission electron microscopy. It has been shown that γ-Fe2O3nanocrystals are isolated from each other and uniformly dispersed in silica matrix. The phase stability of maghemite nanocrystals was examinedin situunder laser irradiation by Raman spectroscopy and compared with that resulting from heat treatment by X-ray diffraction. It was concluded that ε-Fe2O3is an intermediate phase between γ-Fe2O3andα-Fe2O3and a series of distinct Raman vibrational bands were identified with the ε-Fe2O3phase. The structural transformation of γ-Fe2O3intoα-Fe2O3occurs either directly or via ε-Fe2O3, depending on the rate of nanocrystal agglomeration, the concentration of iron oxide in the nanocomposite and the properties of silica matrix. A phase diagram is established as a function of laser power density and concentration.
authors.affiliation: Institut des Molécules et Matériaux du Mans, UMR CNRS 6283, LUNAM Université , Le Mans , France.
authors.forename: Yassine
authors.initials: Y
authors.lastname: El Mendili
authors.affiliation: Institut des Molécules et Matériaux du Mans, UMR CNRS 6283, LUNAM Université , Le Mans , France.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Bardeau
authors.affiliation: Institut des Molécules et Matériaux du Mans, UMR CNRS 6283, LUNAM Université , Le Mans , France.
authors.forename: Nirina
authors.initials: N
authors.lastname: Randrianantoandro
authors.affiliation: Institut des Molécules et Matériaux du Mans, UMR CNRS 6283, LUNAM Université , Le Mans , France.
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Greneche
authors.affiliation: Institut des Sciences Chimiques de Rennes, CNRS UMR 6226, Université Rennes 1, Rennes, France; CNRS-Saint Gobain, Laboratory for Innovative Key Materials and Structures, UMI 3629 LINK, National Institute of Material Science, Tsukuba, Japan.
authors.forename: Fabien
authors.initials: F
authors.lastname: Grasset
keywords: 10 Engineering and Structural materials; 103 Composites; 212 Surface and interfaces; 306 Thin film / Coatings; Nanocomposites; Raman; laser irradiation; phase transformations; silica matrix; sol-gel; ε-Fe2O3