Fe 2 O 3 –SiO 2 composites obtained by sol–gel synthesis Cecilia Savii a, * , Mihaela Popovici a , Corina Enache a , J. Subrt b , D. Niznansky b , Snejana Bakardzieva b , C. Caizer c , I. Hrianca c a Inorganic Chemistry Laboratory, Timisoara Brh., Romanian Academy, 24 Mihai Viteazul Blvd., 1900 Timisoara, Romania b Department of Solid State Chemistry, Institute of Inorganic Chemistry, Academy of Sciences of the Czech Republic, 250 68 Rez, Czech Republic c Physics Faculty, Vest University of Timisoara, 4 V. Parvan Boulevard, 1900 Timisoara, Romania Received 6 February 2001; accepted 15 November 2001 Abstract The present work deals with the synthesis of Fe 2 O 3 – SiO 2 composites, obtained by embedding iron oxide particles in a silica matrix, through sol – gel method based on hydrolysis and condensation of a silicon alkoxide and thermal treatment. Methods employed in characterisation of the materials obtained at different iron concentration and at suitable thermal treatments are infrared spectroscopy, X-ray diffraction analysis and SEM analysis. In purpose to evaluate magnetic properties of these composites, static magnetic and Mo ¨ssbauer spectra measurements were carried out. D 2002 Elsevier Science B.V. All rights reserved. PACS: 81.20.Fw; 75.0; 75.50.Tt Keywords: Sol – gel processing; Magnetic properties; Fine – particle systems 1. Introduction Presently, there is a great interest in synthesis of iron and iron oxides particles embedded in silica matrix that have potential application to information storage, magnetic refrigeration, magneto-optical solid devices, magnetic resonance imaging enhancement, etc. The sol–gel process has been applied to synthe- size a new class of composite materials called dipha- sic gels [1,2]. These materials are gel hosts for the precipitation of a second phase on an extremely fine scale [3–6]. To form such a gel host for iron oxide particles, silicon alkoxides can be conveniently used, the resultant silica matrix having pores that both minimize the upper dimension of precipitated phase and isolate particles from each other [4,7–10]. It is well known that the composition and structure of Fe(III) (hydrous) oxides formed in water depend on the preparation condition, such as Fe 3+ concentration, the nature of the anion present, and pH [11]. Hydrol- ysis of the iron salts proceed by the formation of monomers and dimmers of Fe(III) ions, followed by the condensation of polymeric species. The polymers formed using nitrate are presumed not to include the nitrate ions in the polymer chain, smaller particle size in case of nitrate compared with chloride precursors. The next step in the precipitation process is the formation of oxybridges and the development of oxy-hydroxide structures [8]. From nitrate solution a-FeOOH is usually obtained which transforms to a- 0167-2738/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0167-2738(02)00713-0 * Corresponding author. Tel./fax: +40-56-191816. E-mail address: cecilias@acad-tim.utt.ro (C. Savii). www.elsevier.com/locate/ssi Solid State Ionics 151 (2002) 219 – 227