Structural characterization of TiO 2 ultrafine particles

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Structural characterization of TiO2 ultrafine particles Yingchun Zhu Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, 200050, People’s Republic of China

Tiao Liu Solid State Physical Laboratory, Henan University, Kaifeng, 475001, People’s Republic of China

Chuanxian Ding Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, 200050, People’s Republic of China (Received 17 September, 1997; accepted 9 July, 1998)

Four samples of TiO2 ultrafine particles (UFP) were obtained through different processes. The structure of TiO2 ultrafine particles and the factors influencing the structure were investigated with Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and x-ray diffraction (XRD). Both Raman spectra and x-ray diffractograms show the similar regularity of the phase transformation among the four samples. The observed bimodal lineshape-structure in the Raman spectra is attributed to the intragrain and grain-boundary components of TiO2 UFP. The crystal structure of TiO2 UFP is found to be distorted by the surface structure such as OH and OCH2 CH3 groups coordinated on the surface of TiO2 UFP.

I. INTRODUCTION

Ultrafine particles (UFP) with dimensions distributed in the range of 1–100 nm are also called nanostructured materials. For the reason of their different structures and properties comparing with their coarsergrained counterparts, they have been synthesized and characterized by a variety of methods.1–3 The methods to synthesize ultrafine particles are various, including solgel process,4 dc reactive magnetron sputtering,5 flame reaction,6 gas-condensation process,7 hydrolysis of metal alkoxides,8 etc. The synthetic methods have great influence on the UFP structure.9 TiO2 UFP are one of the materials that have been extensively studied. Raman spectroscopy was used by Haro-Poniatowski4 to study the crystallization of TiO2 UFP from amorphous to the anatase and finally to the rutile phase. Melendres and Parker et al.7,10 utilized macro-Raman and micro-Raman spectroscopies studying nanophase TiO2 and found that the Raman spectra were irrelevant to the particle size but dependent on intragrain oxygen deficiency. These investigations eliminated grain boundaries from being responsible for the shifted Raman spectrum. Ohsaka and co-workers11 found that the frequencies of Raman active modes in the anatase phase were dependent on pressures, and their results showed that the frequency of the 197 cm21 mode decreased with increasing pressure. X-ray diffraction has been widely used to determine the crystal structure and the particle size of TiO2 UFP.6 Infrared spectroscopy has also been used to study the surface structure of titania.12,13 442

J. Mater. Res., Vol. 14, No. 2, Feb 1999

19 Anatase belongs to the space group D4h (I41yamd), its primitive unit cell contains two formula units and has six Raman active modes and three infrared active modes.15 So, in this paper, Raman and infrared spectroscopies as well as x-ray diffrac