Elsevier

Ceramics International

Volume 39, Issue 2, March 2013, Pages 1271-1276
Ceramics International

Multilayer zirconium titanate thin films prepared by a sol–gel deposition method

https://doi.org/10.1016/j.ceramint.2012.07.058Get rights and content

Abstract

Zirconium titanate multilayer thin films were prepared by an aqueous particulate sol–gel process followed by spin coating. The obtained structures were studied by transmission electron microscope, scanning electron microscope, atomic force microscope, and spectroscopic reflection analyses. According to the results, sound thin films up to three layers were developed, accompanied by an increase in thickness and roughness by increasing the number of the layers. It was also found that the coatings consist of globular nanoparticles with an average diameter of 50 nm. Considering the contribution of roughness to biological responses, the optimization of the surface characteristics to meet an optimal performance seems to be a challenging issue, which demands future studies.

Introduction

Zirconium titanate (ZrTiO4), with the orthorhombic α-PbO2 type structure in powder, fiber, coating, and bulk forms, is a ceramic considered in electronic, optical, chemical, catalytic, and biomedical purposes [1], [2], [3], [4], [5], [6]. Typically, ZrTiO4 thin films and coatings have attracted much attention especially in dielectric applications demanding a high resistivity and dielectric constant [7] and more recently in biomedical applications requiring biocompatibility and bioactivity [6], [8]. To process thin films and coatings, among the various methods used, the sol–gel deposition process has advantages such as high homogeneity (as mixing occurs on the atomic level), low sintering temperatures (due to small particle sizes), and simplicity of complex shape coating [9], [10].

Although widespread studies have been conducted on lead zirconate titanate (PZT), titania (TiO2), and zirconia (ZrO2) films, little systematic work has been reported on ZrTiO4 coatings and thin films, especially those considered in biomedical fields and those prepared by the sol–gel route. Referring to the literature, for instance, physical, mechanical, and tribological characteristics of ZrTiO4 coatings prepared by magnetron sputtering for orthopedic and dental implants have been reported [6]. In addition, the thickness dependency of dielectric properties of ZrTiO4 thin films developed by a surface sol–gel process using butoxides as the precursor has been studied [11]. Bavya Devi et al. [8] have also investigated the structure and bioactivity of ZrTiO4 coated on a biomedical stainless steel by a non-hydrolytic sol–gel method starting from titanium tetraisopropoxide and zirconium oxychloride. However, facile, inexpensive, and high-quality processing of materials is an essential concern from both the scientific and technological viewpoints. Recently, an aqueous particulate sol–gel method using chlorides as the precursor was successfully experimented to synthesize ZrTiO4 nanoparticles [12]. Compared to the polymeric sol–gel methods, the typical advantage of this facile route is employing chlorides rather than alkoxides as the precursor to develop a product at lower cost. In this paper, the structure of multilayer thin films obtained from the aforementioned particulate sol–gel method followed by spin coating is characterized by transmission electron microscopy, field emission scanning electron microscopy, atomic force microscopy, and spectroscopic reflection. Additionally, a natural polymer, namely carboxymethyl cellulose was used to improve the dispersion of the synthesized nanoparticles in the aqueous sol.

Section snippets

Experimental procedures

Initially, 9.1 mmol of zirconium tetrachloride (ZrCl4, Alfa Aesar, 99.5%) and titanium tetrachloride (TiCl4, Alfa Aesar, 99.99%) were added to 200 mL of deionized water and magnetically stirred for 2 h. Afterwards, the pH value of the solution was enhanced to 7 by adding 2 M NaOH solution dropwise. The hydrogel was rinsed several times with deionized water to remove chloride ion and centrifuged at 6000 rpm for 10 min. To prepare a sol of appropriate viscosity for spin coating, 75 mL of deionized water

Results and discussion

The maximum sound film thickness obtained in one deposition step, which is limited initially by agglomeration on the substrate rather than a desirable coverage and then cracking during firing, was determined by varying the amount of deionized water used in the sol for the same spin coating condition. When the viscosity is increased by decreasing the water content to less than that used in this work (75 mL for 9.1 mmol of ZrCl4 and TiCl4 with a viscosity of 80 mPa s), the sol does not cover the

Conclusions

Multilayer thin films prepared by an aqueous particulate sol–gel method using CMC as the dispersant were focused. From this work, the following conclusions could be drawn:

  • The development of well-covering, crack-free, and homogeneous ZrTiO4 thin films was confirmed by SEM and AFM, suggesting the merit of processing.

  • A non-linear increase in the thickness and roughness of the multilayer films was found by increasing the number of the layers up to three, realized by the spectroscopic reflectometer

Acknowledgments

This work was partially supported by the AFOSR under Grant no. FA9550-10-1-0010 and the National Science Foundation (NSF) under Grant no. 0933763. Also, Mr. M.J. Modarres and A. Tahmasbi Rad affiliated to the Oklahoma State University are acknowledged for their technical assistance.

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