RESEARCH ARTICLE Copyright © 2008 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Nanoscience and Nanotechnology Vol. 8, 1–7, 2008 X-Ray Diffraction, and Raman Scattering Study of Nanostructured ZrO 2 -TiO 2 Oxides Prepared by Sol–Gel M. E. Manriquez 1 , M. Picquart 2 , X. Bokhimi 3 , T. López 1 , P. Quintana 4 , and J. M. Coronado 5 ∗ 1 Departamento de Química, 2 Departamento de Física, Universidad Autónoma Metropolitana-Iztapalapa, Apdo. Postal 55-534, México DF 09340, Mexico 3 Instituto de Física, Universidad Nacional Autónoma de Mexico, Apdo. Postal 20364, México DF 01000, Mexico 4 Departamento de Física Aplicada, Cinvestav, Unidad-Merida, Carretera antigua a Progreso km 6, Merida Yucatan 97310, Mexico 5 Aplicaciones Ambientales de la Radiación Solar, CIEMAT, Av. Complutense, 22, Bld. 42. 28040 Madrid, Spain In the present work, we study the phase composition of the ZrO 2 -TiO 2 system by means of XRD and Raman spectroscopy, using also TG-ATD, and N 2 adsorption isotherms as complementary characterization techniques. TiO 2 -ZrO 2 samples of selected compositions (0, 10, 90, 50 and 100% in weight of TiO 2 ) were prepared by sol–gel method and annealed at three different temperatures (400, 600 and 800  C). Structural characterization reveals that only the pure oxides are crystalline at 400  C: TiO 2 as anatasa with a minor brookite component, and ZrO 2 as a mixture of tetragonal (majority) and monoclinic phases. Following the 600  C calcination, the TiO 2 -ZrO 2 50–50% sample forms the ZrTiO 4 mixed oxide, although this materials remains partly amorphous. In contrast, the samples with higher and lower TiO 2 content form solid solutions with, respectively, anatasa and tetragonal ZrO 2 structures. Zirconium incorporation into the TiO 2 lattice leads to the expansion of the unit cell parameters, and it stabilizes the anatase phase, hindering its transformation into rutile. Similarly, dissolving titanium atoms into the ZrO 2 structure delays the transformation from the tetragonal to the monoclinic polymorph. Keywords: TiO 2 , ZrO 2 , Mixed Oxides, Nanoparticles, Rietveld Analysis, Raman Spectroscopy, Phase Diagram. 1. INTRODUCTION In many technological fields, the use of mixed oxides is an attractive strategy to produce materials with superior properties than the single components. In particular, mixed oxides have been widely used in catalysis, 1–3 because the surface characteristics of the individual oxides can be changed due to the formation of new sites in the interface between the components, 4 or by the incorporation of one oxide into the lattice of the other. 5 In this last case, mix- ing of the oxides can produce new crystallographic phases with quite different properties than the original oxides. 6 Frequently, the improvement of the activity and the selec- tivity after mixing is associated with the creation of surface defects or with the formation of Brönsted acid sites. 7 8 On the other hand, the variation of the physicochemical prop- erties with decreasing the crystalline size to the nanoscale, opens up another way to tune the characteristics of these solids. Such modifications can be beneficial for catalysis and other applications, due to the increment of the surface area and the density of reactive sites. ∗ Author to whom correspondence should be addressed. In addition to its uses as sensor and refractory ceramic, zirconium oxide is an important catalyst support, since it can present acidic and basic properties. During the last decades, nanocrystalline zirconia has been produced by using different methods, 9–15 although sol–gel process seems to be the most favored. Zirconia has three stable crys- talline phases, tetragonal, monoclinic and cubic, which appears in different proportion depending on the prepara- tion conditions. 14 Zirconia crystals of nanometric size facil- itate the sintering at low temperature, 12 and the stabiliza- tion of the tetragonal polymorph. 16 Furthermore, the use of nanostructured ZrO 2 as a catalytic support is preferred by its high surface area. 17 Similarly, titanium dioxide is also extensively used as catalyst support 18 or as photocatalyst, 19 and it also has three polymorphs which can be prepared under normal conditions: brookite, anatase and rutile. 19 Zirconium and titanium cations are isovalent although they present a significantly different ionic radii: 0.68 Å for Ti 4+ and 0.80 Å for Zr 4+ . They can form mixed oxides, although the only stoichiometric compound formed under atmospheric pressure is the ZrTiO 4 , which presents interesting dielectric properties. 20 Zirconium and titanium J. Nanosci. Nanotechnol. 2008, Vol. 8, No. 11 1533-4880/2008/8/001/007 doi:10.1166/jnn.2008.041 1