Preparation and characterization of BaTiO3 powders and ceramics by sol–gel process using oleic acid as surfactant

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Abstract

The BaTiO3 xerogels, powders and ceramics were prepared via the sol–gel process using oleic acid (OA) as the surfactant. They were characterized by DSC-TGA, FT-IR, XRD, SEM and TEM analysis, and then the dielectric properties of the ceramics were also investigated. The results indicated that the powders calcined at 900 °C for 2 h were pure BaTiO3, partly consisted of the tetrahedron BaTiO3 phase. The particle size of BaTiO3 was between 20 and 50 nm. With the increase of the concentration of OA, the dispersibility of the powders was improved. After sintering, the ceramics were completely consisted of the tetrahedron BaTiO3 phase. The average grain size and the relative density decreased as [Ti(OBu)4]/[OA] ratio increased from 1:1 to 4:1. Moreover, the Curie temperatures of the ceramics ([Ti(OBu)4]/[OA] ratio of 1:1–4:1) were all about 120 °C, and the room temperature permittivity were all higher than 3000. The ceramic ([Ti(OBu)4]/[OA] ratio of 1:1) had the maximum relative density (98.5%) and maximum room temperature permittivity (4569).

Introduction

BaTiO3 with a perovskite structure is noteworthy for its exceptional dielectric, piezoelectric, electrostrictive and electrooptic properties with corresponding electronic applications, and is mostly used to make multilayer ceramic capacitor (MLCC) materials [1], [2]. Various studies are performed to investigate the prepared methods of BaTiO3 nanoparticles. The traditional solid-state method has strict criterion on particle size and purity of raw material, and as it is easy to produce inhomogeneous powders, this would seriously affect the stability of product performance. The familiar wet chemical routes, such as precipitation method [3], hydrothermal law [4], microemulsion approach [5] and sol–gel process [6], which have been developed to offer many advantages. These include better processibility, phase purity, homogeneity and controlled stoichiometry. The monodispersed BaTiO3 nanoparticles can be obtained by hydrothermal law and microemulsion approach. Among these methods, the former three have complicated technological conditions, all refer to washing process, and are hard to control in actual production. In particular, the sol–gel process has been intensively studied. This is because it is so effective to give ceramic powders of high purity, small size and good homogeneity at relatively low temperature. The BaTiO3 nanoparticles synthesized by sol–gel process however are easy to form agglomeration. This can be avoided by the application of the surfactant, thus preventing the agglomeration of particles. The sol–gel process by the addition of surfactant can help to enforce size controllability and prepare well-dispersed powders [7]. However, there are still some drawbacks in this reference, such as the complicated prepared condition and the costly, noxious surfactant. In this paper, we desire to synthesis better dispersed BaTiO3 nanocrystalline powders by sol–gel process using oleic acid as cheap and innoxious surfactant. To our knowledge, the investigation has not been reported before. The synthesis mechanism and the influence of oleic acid on the microstructures and crystal structure of powders and ceramics are also investigated. Finally, the dielectric properties of the ceramics are simply discussed.

Section snippets

Chemicals and equipments

Ti(OBu)4, Ba(Ac)2 and OA(C17H34COOH) were all reagent grade and made in China.

Measurement of the xerogel ([Ti(OBu)4]/[OA] ratio = 1:1) was performed on a thermoanalyzer (DSC-TGA; SDT Q600, American TA Company) in the temperature range from 30 to 1000 °C (10 °C/min) and a dynamic air atmosphere. And Fourier transform infrared (FT-IR) spectroscopic measurements of the xerogels prepared with different heat treatment temperature were made using a IR spectrophotometer (Brucker-Tensor 27, Germany) with a

Thermal analysis of the xerogel

Fig. 1 shows TGA and DTG curves of the thermal decomposition process of the BaTiO3 xerogel ([Ti(OBu)4]/[OA] ratio = 1:1), and Fig. 2 shows DSC curve of the xerogel accordingly. As is shown in Fig. 1, the total weight loss of the xerogel was approximately 57% and the decomposition process can be divided into three distinct steps. The first weight loss in approximately 50–150 °C is due to the vaporization of residual water and organic solvents, corresponding to a quite weak weight loss differential

Conclusions

  • 1.

    The BaTiO3 powders with [Ti(OBu)4]/[OA] ratio of 1:1–4:1 were prepared by sol–gel process using OA as the surfactant. The powders calcined at 900 °C for 2 h were all pure BaTiO3 phase partly consisted of the tetrahedron BaTiO3 phase. They were all nanometer scale with a particle size ranging from 20 to 50 nm. The powders prepared with [Ti(OBu)4]/[OA] ratio of 1:1 had the correspondingly uniform distribution.

  • 2.

    The function of OA in the solution is similar as acetic acid. It reacted with Ti(OBu)4 and

Acknowledgements

This work was supported by Key Research Fund of Shaanxi Key Laboratory (Nos. 04JS04, 05JS50) and Natural Science Foundation of Shaanxi Province (No. 2005B19).

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