| Barium strontium titanate(Ba1-xSrxTiO3,BST)is a continuous solid solution of SrTiO3 and BaTiO3.With the development of miniaturization and refinement of modern electronic components,requirments to nanopowders preparation is becoming more and more important.Barium strontium titanate powders with finer grains,uniform particle size and high purity are widely demanded by the industry.In this paper,barium strontium titanate nano powders were prepared by monhydrolytic sol-gel method.Firstly,the effects of the types of barium sources,strontium sources,titanium sources,and solvents on the synthesis of strontium barium titanate powder were systematically investigated.The results show that Ba-O-Ti and Sr-O-Ti bonds are generated through heterocondensation reaction,with Ba(CH3COO)2 as the barium source,Sr(CH3COO)2 as the strontium source,Ti(OC4H9)4 as the titanium source and glycerol as the solvent,thus ensuring the low-temperature synthesis of Ba0.6Sr0.4TiO3 powders.BaCO3 and SrCO3 have a molecular structure similar to formate,which can be regarded as the combination product of formic acid with barium and strontium after removal of two atoms of hydroge,and can also undergo nonhydrolytic heteropolycondensation.This discovery expands the range of raw material selection for NHSG method.Subsequently,the effects of precursors concentration and(Ba+Sr)/Ti molar ratio on the synthesis of Ba0.6Sr0.4TiO3 powder were studied.The results show that the impurity phase of barium carbonate is generated when(Ba+Sr)/Ti molar ratio is 1:1.An appropriate excessive amount of Ti(OC4H9)4 is beneficial for the synthesis of pure Ba0.6Sr0.4TiO3 powder.The preferred molar ratio of(Ba+Sr)/Ti is 1:1.2.At this time,the particle size is mainly between 17-40 nm,and all elements are evenly distributed.Further,the synthesis of Ba1-xSrxTiO3 powders with different Ba/Sr ratios was also studied.Pure phases are prepared for Ba0.5Sr0.5Ti03,Ba0.6Sr0.4TiO3,Ba0.7Sr0.3TiO3 and Ba0.8Sr0.2TiO3 at Ba:Sr:Ti ratios of 0.5:0.5:1.2、0.6:0.4:1.2、0.7:0.3:1.3 and 0.8:0.2:1.4,respectively.With the increasing of strontium content,the crystallinity of Ba1-xSrxTiO3 increases gradually,and the lattice constant and cell volume decrease.These are because the ionic radius of Sr2+ is smaller than that of Ba2+,and the bond length of Ba-O bond and Ti-O bond also decrease.On the basis above,in order to improve the dispersion of the powder,the effects of the type of dispersant and the addition amount of dispersant on the synthesis and dispersion of Ba1-xSrxTiO3 powder were researched.It is found that when Tween 60 is selected and the addition amount is 1.0 wt.%,the dispersion effect is the optimized.At this time,the particle size distribution is the narrowest,indicating that Ba0.6Sr0.4TiO3 powder then has the most uniform distribution.DTA-TG-MS curves of exgel confirm that a large amount of gas escapes from at 200℃-400℃ and 400℃-600℃,and the MS curve at 900℃ is relatively flat,indicating that other organic groups are basically eliminated at 900℃.Meanwhile,the gel sample heat-treated at 900℃ has excellent crystallization.Therefore,the optimal heat treatment temperature for the powder is 900℃.The optimized sintering system for Ba0.6Sr0.4TiO3 ceramics is sintered at 1300℃ for 6 hours.The relative density and the porosity of the sintered Ba0.6Sr0.4TiO3 ceramics are 98.1%and 0.3%,respectively. |
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