INTRODUCTION Nanocrystalline materials are currently receiving much attention by virtue of their chemical, physical and mechanical properties. TiO2 nanoparticles are gaining much attention due to crystal structure, nanoparticle size, morphology and the method of synthesis. TiO2 has three naturally occurring poly- morphous: anatase, rutile and brookite. Among them, the TiO2 exists mostly rutile an anatase phases, which both of them have the tetragonal structures. However rutile is a high-tempe- rature stable phase and has an optical energy band gap of 3 eV (415 nm), anatase is formed at lower temperature with an optical energy band gap of 3.2 eV (380 nm) and refractive index of 2.3 1 . The size of the TiO2 particles is a considerable parameter that influences physical and chemical properties of materials, so that most of the recent researches have been focused upon the reaction of the particle size. The use and performance of mixed polymorphs in various applications are strongly influenced by the particle size, crystallite size, degree of crysta- llinity and morphology 2 . The anatase and rutile phases and phase transformation have been examined extensively. Many researchers intend to gather information on these phases and transition. Among the many chemical techniques for the fabrication of materials, sol-gel processing as a moderate and adjustable method has emerged as an alternative route to control the size, Structural Properties, Lattice Strain and Transformation of Anatase-Type TiO 2 Nanocrystals to Rutile in TiO 2 -SiO 2 Composite MEHRAN RIAZIAN, SHIMA DALIRI RAD, NASER MONTAZERI and KHALIL POURSHAMSIAN * Department of Chemistry, Tonekabon Branch, Islamic Azad University, Tonekabon, Iran *Corresponding author: E-mail: kh_pourshamsian@toniau.ac.ir (Received: 23 November 2011; Accepted: 26 July 2012) AJC-11878 We report the synthesis of TiO2 nanoparticles in anatase and rutile structures in SiO2-TiO2 composite. The SiO2-TiO2 nanostructure was synthesized based on the sol-gel method. The nanoparticles were characterized by X-ray fluorescents, X-ray diffraction, field emission scanning electron microscopy and Fourier transmission infrared absorption (FTIR) techniques. Phase formation was achieved by hydro- thermal treatment at elevated temperatures. The anatase nanoparticles were obtained under 300 ºC calcined temperature, while rutile phase were obtained in higher than 300 ºC calcined temperature. The mass fraction of anatase and rutile phases was calculated. It can be fined that as the calcined temperature increases the per cent of rutile phase content grows, as well as when the content of TiO2 in SiO2-TiO2 composite increases, the per cent of rutile phase content grows. The effects of chemical compositions and calcinations temperature on the surface topography and the crystallization of phases were studied. Key Words: Nanostructure, Phase characterization, SiO2-TiO2, Sol-Gel method. morphology, structure and physical and chemical properties of inorganic oxides 3 . The sol-gel process is commonly applied to synthesize TiO2 materials owing to its several advantages such as low temperature processing and the ability to prepare materials in various shapes, compared with the conventional preparation procedures of glass and ceramics 4,5 . In this study TiCl4 and tetraethyl orthosilicate used as starting materials were hydrolyzed using CH3COOH solution. EXPERIMENTAL In this work we prepare TiO2 by using hydrolysis proce- dure of TiCl4, which is transformed to anatase by heating it at 300, 500, 700 and 900 ºC. It obviously depends on the prepa- ration procedures and TiO2 content in combination. Anatase is generally transformed to rutile if calcinations temperature and TiO2 content increase (Fig. 1). By adding more SiO2 to TiO2, the obtained powder trend to crystalline structure. Fig. 1. Schematic model of anatase and rutile Asian Journal of Chemistry; Vol. 25, No. 1 (2013), 356-364 http://dx.doi.org/10.14233/ajchem.2013.13087