ORIGINAL PAPER Structural and thermal properties of monolithic silica–phosphate (SiO 2 –P 2 O 5 ) gel glasses prepared by sol–gel technique M. Kamal • I. K. Battisha • M. A. Salem • A. M. S. El Nahrawy Received: 29 September 2010 / Accepted: 3 February 2011 / Published online: 17 February 2011 Ó Springer Science+Business Media, LLC 2011 Abstract A sol–gel process for producing monolithic silica–phosphate (SiO 2 –P 2 O 5 ) system different concentra- tions of P 2 O 5 , starting with tetra-ethoxysilane TEOS, and triethyl-phosphate as sources of SiO 2 and P 2 O 5 was per- formed. The gels were heat-treated at temperatures ranging from 100 up to 900 °C. The structural and chemical anal- yses of the samples were determined by using X-ray diffraction (XRD) and Fourier Transform Infrared Spec- troscopy (FTIR). It was found from the XRD that the existence of phosphorus enhances the crystallization of silica gel, while the FTIR indicated the main functional groups of silica–phosphate. It is important to study the effect of hydroxyl in silica–phosphate glass. The results obtained are promising to use the prepared samples in a variety of applications, ranging from traditional application such as lighting products) to the modern application (such as optical fibers. Optical studies were measured by using the spectrophotometer in wavelength range 0.2–2.5 lm. The refractive index (n) was calculated for the prepared samples, it was found to be strongly affected by structural rearrangement resulting from the elimination of the solvent and the Si–OH, Si–O–Si and Si–O–OH bonding by phos- phate and aluminum and it increases by increasing phos- phate concentrations. The weight losses have investigated for prepared samples. Keywords Sol–gel  Gelation  Silica–phosphate glass  FTIR 1 Introduction In recent years, materials consisting of semiconductor nano- crystals embedded in a dielectric matrix have attracted considerable attention, thus silica–phosphate gels have attracted much attention and many works have been carried out because of their potential technological applications such as optical fibers for optical communication systems and coatings [1–3], electrolytes for high energy density batteries [4, 5], hydrogen fuel cells [6] and medical implants [7]. Therefore, the synthesis and characterization of vitre- ous silica–phosphate compounds prepared by sol–gel pro- cesses, using different SiO 2 :P 2 O 5 ratios and precursors have deserved the attention from several authors [8–14]. The sol–gel process is a promising chemical synthesis route that offers several advantages such as purity, high chemical homogeneity, lower calcinations temperatures, particle size control and modifications of material properties by chang- ing fabrication parameters [15]. The mean pore size, the interconnectivity and the pore size distributions can be controlled by changing the molar ratio water/precursor, type of catalyst, type of precursor, temperatures of gelation, drying, and stabilization [16]. Nowadays, sol–gel chemistry provides a means for preparing precursors in which the mixing of two or more phases can be controlled on the nano-scale or even molecular level.The specific uses of these sol–gel produced glasses and ceramics are derived from the various material shapes generated in the gel state, i.e., monoliths, films, fibers, and mono-sized powders. The sol–gel process, as the name implies, involves the evolution of inorganic networks through the formation of a M. Kamal Physics Department, El Mansoura University, Mansoura, Egypt I. K. Battisha (&)  M. A. Salem  A. M. S. El Nahrawy Department of Solid State Physics, National Research Center, NRC, Doki, Giza, Egypt e-mail: szbasha@yahoo.com 123 J Sol-Gel Sci Technol (2011) 58:507–517 DOI 10.1007/s10971-011-2420-0