**1. Introduction**

10 Will-be-set-by-IN-TECH

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Sol–gel process [1-3] is an attractive alternative to other methods for synthesis of ceramics and glasses for many reasons: for example, low temperature synthesis, simple equipment's to be used, thin film formability and so on. Particularly, sol–gel process is very useful for thin film deposition because of the capability to coat materials of various shapes and/or large area, to control the composition easily for obtaining solutions of homogeneity and controlled concentration without using expensive equipment.

Historically, metal alkoxides have been employed in sol–gel process, which readily undergo catalyzed hydrolysis and condensation to form nanoscale oxide or hydroxide particles. Still in general, metal alkoxides are often used as raw materials in sol–gel process, but many of the alkoxides are very difficult to be obtained because of the high sensitivity to the atmospheric moisture [4-9]. In ordinary sol–gel processing, starting compositions as well as reaction conditions are selected so as to maintain the mixture in a homogeneous state throughout the processes including mixing of starting compounds, gelation, aging, drying and heat-treatment.

Titanium and zirconium oxides are very promising candidates for future technology of thin layers because of their interesting mechanical, thermal and chemical properties. Titanium oxide (TiO2) is a cheap, non-toxic, and non-biodegradable material, besides their widely uses in various industries [10]. Moreover, it is a semiconductor under the form of thin films. Its insensitivity to visible light due to its band gap (3.2 eV) enables it to absorb in the near ultraviolet region [11], even though its low efficiency. Hence, it can be sensitized by a great number of dyes; some of them allow a conversion rate incident photon–electron approaching unity. Thus, these various applications arouse great interest in the study of

© 2012 Bensaha and Bensouyad, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Bensaha and Bensouyad, licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### 208 Heat Treatment – Conventional and Novel Applications

titanium oxide thin films. The significant uses of TiO2 thin films are in solar cells [12], photocatalytic [13] and electro-chromic systems [14], in other words, they are mainly found their use in optics.

Synthesis, Characterization and Properties of

Zirconium Oxide (ZrO2)-Doped Titanium Oxide (TiO2) Thin Films Obtained via Sol-Gel Process 209

structural and optical properties resulting from different annealing treatments and different layer thicknesses: X-ray powder diffraction, Fourier transforms infrared (FTIR), Raman spectroscopy, Scanning electron microscopy (SEM), differential scanning calorimetric (DSC), Scanning electron microscopy (SEM), the energy dispersive X-ray spectrometry (EDX) and

To obtain nanomaterial's with controlled properties, it is most often involves the use of mineral additives (dyes, semiconductors, metal particles, rare earth, etc.) in small quantities. These additions can promote densification or control the phenomenon of grain growth, or to change the structural, physical and optical properties. So the presence of impurities in a matrix can stabilize, improve or modify the various properties of a material. Generally, thin layers of doped TiO2 give hope of significant performance gains and new applications.

Our 5% ZrO2-doped TiO2, thin lms were prepared by dip coating, in three steps. The rst step: the dissolution of 1 mol of butanol (C4H9OH) as solvent, 4 mol of acetic acid (C2H4O2), 1mol of distilled water and 1 mol of tetrabutylorthotitanate (C4H9O)4Ti. In the second step, the solution of ZrO2 was prepared from the dissolution of 1 mol of zirconium oxychloride salt (ZrOCl2•8H2O) in distilled water and 2 mol of ethanol (95%) as catalyst. Finally, the solution of TiO2 was doped with ZrO2. Then, the resultant yellowish transparent solutions were ready for use. The substrates were dip-coated in the solutions at a constant rate of 6.25 cm.s-1. After each dipping, thin lms were dried for 30 min at a distance of 40 cm from a 500 W light source. The drying temperature of the light source is approximately equal to 100 °C. Subsequently, thin lms were heat treated in the temperature range 350–450 °C, with a temperature increase rate of 5°C.min-1, for 2 h in the furnace. The powders obtained from

After each dipping, the thin films were dried for 30 min, at a distance of 40 cm from a 500 Wight source. The drying temperature of the light source is approximately equal to 100 °C. Subsequently, thin films were heat treated in the temperature range 350–450 °C, with a temperature increase rate of 5 °C min-1, for 2 h in the furnace. The powders obtained from the xerogel were prepared with an annealing till three months in room temperature and

To investigate the transformation behaviors and the effect; of a smaller ratio range of ZrO2; doping on the surface area of TiO2 thin films, light absorption, band gap energy, variations of crystal granularity, phase composition and especially on the evolution of the crystallite size and defects concentration with annealing treatments (heat treatments) and layers

So that in this chapter, we report the study of structural, thermal and optical properties of

Several experimental techniques were used to characterize structural and optical properties resulting from different annealing treatments and different layer thicknesses: X-ray powder

the xerogel were prepared in room temperature and under air atmosphere.

UV spectroscopy.

**2. Experiments** 

under air atmosphere.

thickness of the samples produced.

ZrO2-doped TiO2 thin films deposited by the sol–gel process.

TiO2 thin films are extensively studied because of their interesting chemical, electrical and optical properties [15,16]. TiO2 film in anatase phase could accomplish the photocatalytic degradation of organic compounds under the radiation of UV. So, it has a variety of application prospects in the field of environmental protection [17,18]. TiO2 thin film in rutile phase is known as a good blood compatibility material and can be used as artificial heart valves [19]. In addition, TiO2 films are important optical films due to their high reflective index and transparency over a wide spectral range [16].

During the two last decades, several methods have been used for the TiO2 thin films preparation, such as chemical vapor deposition [20], chemical spray pyrolysis [21], pulsed laser deposition [22] and sol–gel method [23]. In comparison with other methods, the sol–gel method has some advantages such as controllability, reliability, reproducibility and can be selected for the preparation of nano-structured thin films [23,24]. Sol–gel coating has been classified as two different methods such as dip and spin coating.

The dip-coating has considerably been used for preparation TiO2 nanostructured thin films [25–27]. Experimental results have shown that the preparation of high transparent TiO2 thin film by dip-coating method needs to control morphology, thickness of the film and the anatase-brookite-rutile phase transformation [26,28].

Additions of another semiconductor have been used to improve the properties of titanium dioxide. In principle, the coupling of different semiconductor oxides seems useful in order to achieve a higher photocatalytic activity [29]. Various composites formed by TiO2 and other inorganic oxides such as SiO2 [30], ZrO2 [31] SnO2 [32], Cu2O [33], MgO [34], WO3 [35], In2O3 [36], ZnO [37], MoO3 [38], CdS [39], PbS [40], and so on, have been reported.

Zirconium oxide (ZrO2) has good dielectric and optical properties [41,42] it has a high refraction index [43]. Additionally, it has a very good transparency on a broad spectral field [44], a great chemical stability and a threshold of resistance to high laser flow. All these properties led to miscellaneous applications such as optical filters, laser mirrors [45] or barriers layers from the heat [46]. ZrO2 films are also employed as plug layer for superconducting ceramics [47,48], like biomaterial for prostheses [49,50], as gas sensor [51] or like component in combustible batteries [52]. Basically, ZrO2 itself is an insulating direct wide gap metal oxide, with an optical band gap in the range 5.0-5.85 eV [53].

The aim of the present work is to investigate the transformation behaviors and the effect; of a smaller ratio range of ZrO2; doping on the surface area of TiO2 thin films, light absorption, band gap energy, variations of crystal granularity, phase composition and especially on the evolution of the crystallite size and defects concentration with annealing treatments (heat treatments) and layers thickness of the samples produced. So that in this chapter, we report the study of structural, thermal and optical properties of ZrO2-doped TiO2 thin films deposited by the sol–gel process. Several experimental techniques were used to characterize structural and optical properties resulting from different annealing treatments and different layer thicknesses: X-ray powder diffraction, Fourier transforms infrared (FTIR), Raman spectroscopy, Scanning electron microscopy (SEM), differential scanning calorimetric (DSC), Scanning electron microscopy (SEM), the energy dispersive X-ray spectrometry (EDX) and UV spectroscopy.

To obtain nanomaterial's with controlled properties, it is most often involves the use of mineral additives (dyes, semiconductors, metal particles, rare earth, etc.) in small quantities. These additions can promote densification or control the phenomenon of grain growth, or to change the structural, physical and optical properties. So the presence of impurities in a matrix can stabilize, improve or modify the various properties of a material. Generally, thin layers of doped TiO2 give hope of significant performance gains and new applications.
