The Synthesis of Ultrafine Ba/Sr Titanate Powders
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THE SYNTHESIS OF ULTRAFINE Ba/Sr TITANATE POWDERS C.H.Lin, T.S. Yan, and T.S.Chin Dept. of Materials Science, National Tsing Hua University, Hsin Chu, Taiwan ABSTRACT Ba/Sr titanate powders were obtained by reacting TiO2 .xH&O gel in Ba(OHRz and/or Sr(OH)z aqueous solution. Different reaction temperatures between 68*C and 98'C and different mole ratios of Ba(OH) 2 and Sr(OH) 2 were used. X-ray diffraction analysis showed that the titanate powders are cubic, and they are solid solutions of barium and strontium. The lattace spaces of the titanates are affected by the Ba(OH)z/ Sr(OH), mole ratio. TEM analysis showed that the titanate powders were spherical, ultrafine, and almost monodispersed. The particle size of the powders is about from 41 to 50 nm depending on the reaction temperature. The titanate powders were compacted and sintered at various temperatures. The best sintering temperature of the powders is about 150*C lower than that of powders made by solid state sintering method. INTRODUCTION Titanate ceramics are used in capacitors, piezoelectric ceramics, and PTCR(positive temperature coefficient resistors). Titanate ceramics are made from titanate powders by compacting and subsequent sintering of the powders. Traditional titanate powders are made by the solid-state sintering method, by first mixing TiOz and carbonate powders, then calcining the mixed powders. The powders produced by solid-state sintering method have following two disadantages: 1. is not uniform chemically, 2. have wide particle size distribution. The electrical properties can be improved if the titanate powders have a more uniform chemical composition and particle1 Several wet chemical methods, such as sol-gel method' 3 size. and oxalate coprecipitation methodC2s have been reported for the preparation of BaTi03. These two methods can produce chemically uniform powder, but they produce only mixed hydroxides or oxalates. They are unable to produce fine and uniform powder in particle size because pre-sintering and subsequent ball-milling are needed by these methods to prepare BaTiO3 powder. Mat. Res. Soc. Symp. Proc. Vol. 249. 01992 Materials Research Society
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3 Mazdiyasni, Dolloff, and SmithC ] obtained finely divided, stoichiometric BaTiO3 with 5 to 15 nm particles directly from aquous solution by simultaneous hydrolytic decomposition of the alkoxides according to the reaction: Ba(OCH , ), + Ti(OCOH, 1 ) 4 + 3HO -) BaTiO0 + 2CHOH + 4CH, OH The reaction was carried out in a CO,-free atmosphere at 50*C for 12 hr. Mazdiyasni's method is economically unfavorable because it used expensive alkoxides as raw materials. Vivekanandan and KuttyC4 3 produced fine, and microcrystalline BaTiO, powder about 100 nm in size by reacting amorphous TiO5 .xHzO gel in aqueous Ba(OH)g at 90-180 0 C. Theyr5] also produced Ba(Ti,Sn)0 3 fine powders by the same method and measured the dielectric properties of the corresponding ceramics. Lin and his co-workersC 6 3 produced fine and uniform BaTiO3 powder less than 100 nm in size by reacting TiC1 4 with aqueous Ba(
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