Combined use of XAFS, XRD and TEM to unravel the microstructural evolution of nanostructured ZrO 2 –SiO 2 binary oxides: from nanometres down to the molecular domain Fabio Meneghetti, ab Eric Wendel, b Simone Mascotto, ac Bernd M. Smarsly, c Eugenio Tondello, a Helmut Bertagnolli b and Silvia Gross * a Received 4th June 2009, Accepted 15th December 2009 First published as an Advance Article on the web 15th January 2010 DOI: 10.1039/b911004f In this paper, the detailed study of the microstructural evolution under annealing of zirconium-based inorganic–organic hybrid materials to give silica–zirconia mixed oxides was addressed by X-ray absorption fine structure (XAFS) spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The silica materials embedding different amounts of ZrO 2 nanoparticles were prepared by copolymerisation of the organically modified oxozirconium cluster (Zr 4 O 2 (OMc) 12 (OMc ¼ methacrylate)) with methacryloxypropyltrimethoxysilane (MAPTMS). By the free radical copolymerisation of the oxoclusters bearing 12 methacrylate groups with the methacrylate- functionalised siloxanes, a stable anchoring of the clusters to the silica network was achieved. The thermal treatment of these hybrids at high ($500  C) temperatures yielded the SiO 2 –ZrO 2 mixed oxides. The microstructural evolution upon heating was studied at increasing temperatures, namely 500, 600, 700, 900, 1000 and 1300  C. Furthermore, different samples characterised by different Zr : Si atomic ratios and annealed at 1000  C were comparatively analysed to study the effect of the composition on the evolution of the hybrids to give the mixed oxides. In a third experiment, samples characterised by the same composition were annealed at the same temperature by using either a conventional muffle or a microwave oven in order to evidence whether the different processing could also affect the microstructural features of the final oxide materials. Through XRD and XAFS it was demonstrated that at temperatures above 800  C, crystallisation of tetragonal zirconia occurs in the samples of high zirconium concentration treated in muffle, whereas amorphous oxide materials form upon annealing in microwave oven. The presence of zirconia nanoclusters having an average size of 5–10 nm was evidenced by TEM. 1. Introduction The understanding of the properties of nanocomposite materials requires a careful characterisation not only of their composition and microstructure, but also a deep comprehension of their crystallisation behaviour and of the nucleation and growth steps leading to the formation of the nanostructure. This information is a valuable starting point for the following establishment of structure–property relationships and for a better understanding of their stability. Only once these critical stages of inorganic solid crystallisation and the main phenomena occurring on both the nano- and the microscale have been unraveled, the improvement and the tuning of their properties would become possible. Since these changes occur, at different time domains, over the molec- ular (local coordination, chemical environment), nanoscopic (nucleation of primary units) and microscale (growth of crystallites) levels, thus involving different length scales, their investigation by using a single technique can hardly provide all the information on the different size regimes to get an overall insight into the evolution of the system. As a consequence, the key stages of these events can be followed and studied only by combining complementary techniques providing mutually inte- grating and consistent pieces of information on the system at different size scales. To this aim, in this study, we addressed the structural inves- tigation of our binary oxide systems by using XAFS, XRD and TEM methods, covering different length scales, which were set to follow the evolution of the mixed oxides from the nucleation of the first seeds to the complete crystallisation of tetragonal zirconia nanoparticles dispersed in the silica matrix. A combined analytical approach to the study of crystallisation in inorganic solids has been already proposed by several authors and, more recently, Weckhuysen et al. 1 have pioneered a combined SAXS–WAXS–XAFS setup to carry out time- resolved studies on the crystallisation path of zinc-substituted aluminiumphosphates. With respect to these previous studies, we faced the study of the nucleation, growth and crystallisation behaviour of zirconia nanoparticles in a silica matrix also by investigating the effect of a CNR–ISTM, Dipartimento di Scienze Chimiche, Universit  a di Padova, and INSTM UdR Padova, via Marzolo, 1, 35131 Padova, Italy. E-mail: silvia.gross@unipd.it b Institut f € ur Physikal. Chemie, Universit € at Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany c Physikalisch-Chemisches-Institut, Justus-Liebig-Universitaet Giessen, Heinrich-Buff-Ring 58, D-35392 Giessen, Germany This journal is ª The Royal Society of Chemistry 2010 CrystEngComm, 2010, 12, 1639–1649 | 1639 PAPER www.rsc.org/crystengcomm | CrystEngComm