Microstructural evolution of metallorganic derived Pt-doped TiO 2
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Ko-ichi Kikuta and Shin-ichi Hirano Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan (Received 26 October 1999; accepted 12 September 2000)
A metalorganic precursor containing Ti and Pt was synthesized using Ti alkoxide derivative, amino acid, and platinum salt. The decomposition behavior of the precursor and thin-film formation were examined in terms of microstructure evolution and crystallization. The precursor yielded anatase at 400 °C. Grain growth of platinum particles and TiO2 grains was suppressed even at 800 °C in the films. Suppression of grain growth was attributed to an effect of film thickness.
I. INTRODUCTION
TiO2-based materials have received attention because of their heat resistance, chemical stability, semiconducting properties, and photosensitive properties. Therefore, this material has been used for sensors,1–5 catalysts,6,7 and electrodes.8 As a catalyst, it is known that the addition of noble metal to metal oxide enhances the catalytic property.9 In this case, the decrease of particle size of the noble metal is effective for the improvement of the catalytic properties. This is due to the increased number of active sites and the enhancement of surface activity. Moreover, the catalytic properties of TiO2-based materials containing noble metal depend on microstructure, the grain size of the matrix, the dispersion of noble metal, and pore structure. TiO2 powders dispersed with Pt are usually synthesized using TiO2 fine powders or TiO2 sol with Pt salt.10,11 In the former, fine Pt particles of 1.5–4.0 nm in diameter are formed on the surface of TiO2 grains by heating at 480 °C in H2. However, it is not well known how Pt particles are dispersed in TiO2 matrix. This is because catalytic activity considerably decreases due to the decrease of surface area resulting from densification of TiO2 grains. Metalorganic precursor processes are found to be very effective for controlling microstructure on the nanoscale because each element in the precursor is bonded and homogeneously dispersed at an atomic level. Pt remains in the Ti–O network even after precipitation by using a)
Present address: Material Research Laboratory, Corporate Technical Center, NGK Insulators, Ltd., Nagoya, Japan. b) Present address: Japan Fine Ceramics Center, Nagoya, Japan. 2794
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J. Mater. Res., Vol. 15, No. 12, Dec 2000 Downloaded: 19 Apr 2015
such a precursor. Such a highly dispersed state can contribute to the formation of very fine Pt particles and high dispersion of Pt after heating. Microstructure derived from metalorganic precursor depends on the chemical composition and molecular structure of the precursor, heating temperature, and heating atmosphere. This paper describes the microstructure changes from precursors containing titanium and platinum through heating to form powders and thin films.
II. EXPERIMENTAL
Figure 1 is a flow chart showing the synthesis of the precursor solution containing Ti and Pt. A 75% isopropanol solution of Ti(O–iPr)2(AcAc)2 (Nisso, T-50, J
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