**2. Experiments**

208 Heat Treatment – Conventional and Novel Applications

index and transparency over a wide spectral range [16].

anatase-brookite-rutile phase transformation [26,28].

classified as two different methods such as dip and spin coating.

use in optics.

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

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

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

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

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],

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

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

In2O3 [36], ZnO [37], MoO3 [38], CdS [39], PbS [40], and so on, have been reported.

gap metal oxide, with an optical band gap in the range 5.0-5.85 eV [53].

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

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 under air atmosphere.

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 and films diffraction, Fourier transforms infrared (FTIR), Scanning electron microscopy (SEM), Raman spectroscopy, differential scanning calorimetric (DSC), Scanning electron microscopy (SEM), the energy dispersive X-ray spectrometry (EDX) and UV spectroscopy.

Synthesis, Characterization and Properties of

Zirconium Oxide (ZrO2)-Doped Titanium Oxide (TiO2) Thin Films Obtained via Sol-Gel Process 211

**Figure 1.** Variation of lm thicknesses d (nm) with solution viscosity η(mPas.s)

Figure 2a and b shows the X-ray diffraction (XRD) patterns of TiO2 xerogels of undoped (Figure 2a) and 5% ZrO2-doped TiO2 (Figure 2b). The XRD pattern evolution of titanium xerogel obtained after the evaporation of the organic compounds during 3 months of aging

It has been reported that the used acid catalyst, during sol–gel preparation, plays a crucial role for determining the TiO2 phase, in literature [54, 55], they found that powder is amorphous when they use acetic acid as catalyst. However, when using formic acid they found that, in addition to amorphous phase, there is an amount of the anatase nanoparticles. This analysis of the doped TiO2 xerogel exhibits that the addition of 5% ZrO2 (Figure 2b) would be largely sufficient to form nanoparticles of anatase which crystallizes with (101) plane. It is interesting to note that the addition of a minor amount of ZrO2 starts crystallization of anatase. Whereas, A. Kitiyanan et al. [56] B. Neppolian et al. [57] reported

at ambient temperature shows that it is an amorphous phase as reported in [54].

that addition of ZrO2 has no effect on TiO2 oxide morphology..

**3.2. Powder Properties (Xerogel)** 

*3.2.1. X-Ray Diffraction (XRD)* 

To determine the transformation points, the obtained powdered xerogels were analyzed by Differential Scanning Calorimetry (DSC) using a SETARAM DSC–92 analyzer equipped with a processor and a measuring cell. The thermal cycle applied consists of heating from room temperature to 520°C, holding for 5min at this temperature and finally cooling back to room temperature with the same rate (5°C/min). X-ray powder diffraction was performed by Siemens D5005 diffractometer using a Cu Kα1 radiation. The patterns were scanned at room temperature, over the angular range 10-70° 2θ, with a step length of 0.1° 2θ and counting time of 1 s.step-1. The UV absorption studies were carried out using UV-VIS double–beam spectrophotometer SHIMADZU (UV3101PC). Its useful range is between 190 and 3200 nm. The treatment of the spectra was performed using the UVPC software. A surface profiler DEKTAK 3ST AUTO1 (VEECO) was used to determine film thicknesses. Raman spectra were recorded in a back scattering configuration with a Jobbin Yvon micro Raman spectrometer coupled to a DX40 Olympus microscope. The samples of doped and undoped TiO2 thin films were excited with a 632.8 nm wavelength with an output of 20 mw.
