Synthesis of Ba 2 Ti 9 O 20 via ethylenediaminetetraacetic acid precursor
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Liangbin Wang Structure Research Laboratory, University of Science and Technology, Hefei, Anhui, 230026, People’s Republic of China (Received 21 August 2000; accepted 2 February 2001)
The modified Pechini method using ethylenediaminetetraacetic acid as a chelating agent to prepare Ba2Ti9O20 is reported. The resin precursors were prepared and heated at 700 to 1200 °C in air, and x-ray diffraction was used to determine the phase transformations as a function of temperature. Single-phase Ba2Ti9O20 was obtained at 1200 °C for 2–6 h, without the need of prolonged heat treatment time. The process was simple and easy to control: low-temperature conditions or a protective atmosphere was not needed. Differential thermal analysis, thermogravimetric analysis, and Raman spectroscopy were used to characterize the precursors and derived oxide powders. Details of the synthesis and characterization of the resultant products were given.
I. INTRODUCTION
Ba2Ti9O20 ceramics in the system BaO–TiO2 exhibited attractive dielectric properties such as a high dielectric constant, high quality factor, and a small temperature coefficient of resonant frequency.1,2 It is therefore a useful material for microwave resonators and has been widely studied. Ba2Ti9O20 ceramics have been prepared previously by a variety of techniques. Jonker and Kwestroo3 first produced Ba2Ti9O20 by solid-state reaction of BaCO3 with TiO2 at temperatures ranging from 1300 to 1400 °C and concluded that Ba2Ti9O20 was not an equilibrium compound in the binary system BaO–TiO2 and it needed SnO2 or ZrO2 to be stabilized. However, Negas and Roth4 were able to prepare single-phase Ba2Ti9O20 in the binary system BaO–TiO2 and concluded that it was a stable phase in the system and decomposed peritectoidally at 1300 °C. O’Bryan and Thomson5 later confirmed the stability, but they extended maximum stability range to approximately 1420 °C. They also found it was necessary to form some Ba2Ti9O20 during the calcination stage if a single-phase Ba2Ti9O20 ceramic was to be obtained during the sintering stage. Because of the difficulties of the synthesis of Ba2Ti9O20 by a solid-state reaction method, many researchers have studied the synthesis of Ba2Ti9O20 by wet chemical methods. Ritter et al.6 synthesized Ba2Ti9O20 by simultaneous hydrolysis of alkoxides of barium and titanium in an alcohol solution; Ba2Ti9O20 was formed J. Mater. Res., Vol. 16, No. 4, Apr 2001
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after long heat treatment at 1100 °C (543 h). Using a liquid mixing technique (Pechini method11,12), Javadpour and Error7 prepared Ba2Ti9O20 by firing the material produced by reacting barium carbonate with tetraisopropyltitanate in an ethylene glycol–citric acid solution; Ba2Ti9O20 was obtained only after long heat treatment at 1200 °C (110 h). Lu et al. 8 prepared Ba2Ti9O20 by mixing a titania sol produced by the hydrolysis of titanium ethoxide in a methanol medium with a barium methoxide solution in an ice bath, and prolonged heating of precursors at 1200 °C (110 h) pr
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