Sol-gel-hydrothermal Synthesis And Characterization Of BaTiO₃Powder

BaTiO₃is one of the most representative electronic ceramics which is the activist fieldin research. BaTiO₃electronic ceramic called as “Backbone of Electronic CeramicIndustry” is widely utilized in fabricating multilayer ceramic capacitors, thermistors,ferroelectric and piezoelectric devices due to its excellent performance, such asdielectric, ferroelectric, piezoelectric and insulating properties, etc..With the rapid development of electronic information technology, BaTiO₃electronic ceramic is endued with higher requirement on performance, and theperformance of BaTiO₃ceramic depends greatly on the quality of raw material.BaTiO₃powders prepared by traditional solid state reaction have not satisfied theperformance requirement of precision electronic device due to the products possessinglarger particle size and non-uniform size distribution. So it is the practical needs in thedevelopment field of electronic ceramics that developing synthesis method that canprepare BaTiO₃powders with high purity, high crystallinity, small particle size as wellas good dispersion.The preparation methods of BaTiO₃powders in recent years have been summarizedwith their respective advantages and disadvantages compared in this article andBaTiO₃powders was tried to be synthesized by sol-gel-hydrothermal methodcombined sol-gel process and hydrothermal process. The effects of reactant Ba/Ti,hydrothermal temperature, hydrothermal time, molar concentration of mineralizerKOH and different kinds of dispersants （sodium dodecyl benzene sulfonate, SDBS;hexadecyl trimethyl ammonium bromide, CTAB; macrogol6000, PEG6000） on theparticles properties were investigated systematically, and BaTiO₃powders preparedby sol-gel method was also studied comparatively. Moreover, phase structure,composition, particle size and morphology of the as-synthesized products werecharacterized by some modern analysis techniques such as X-ray diffraction （XRD）, scanning electron microscopy （SEM） and Fourier transform infrared spectroscopy（FTIR）. The main results of the thesis are as following:（1） BaTiO₃powders were successfully prepared by sol-gel-hydrothermal methodusing tetrabutyl titanate and barium acetate as titanium source and barium source atthe process parameters of lower hydrothermal temperature （120℃）, reaction time （12h） and lower KOH molar concentration （2.0M）. The as-synthesized products werenear-spherical cubic BaTiO₃particles with high purity and good crystallinity. The sizecontrol of BaTiO₃powders could be realized by changing KOH concentration （1.0M-8.0M）. Raising temperature and prolonging time both promoted the growth ofBaTiO₃crystal. However, when the temperature reached120℃and the time wasprolonged to12h, the crystallinity, particle size and morphology were less influencedby further increasing temperature and time because the growth of BaTiO₃crystalalmost reached an equilibrium and the crystallinity was higher. Increase the reactantBa/Ti or KOH concentration led to the decrease of particles size of BaTiO₃.（2） BaTiO₃powders were also synthesize by traditional sol-gel process with thedry gel precursor calcined at different temperatures. The products obtained by twokinds of different preparation techniques were compared. Well-crystalline cubicBaTiO₃powders could be directly obtained under mild temperature of120℃bysol-gel-hydrothermal method, however, BaTiO₃crystal grew well only when thecalcination temperature reached over800℃by sol-gel process. Moreover, comparedto sol-gel way, the BaTiO₃powders obtained by sol-gel-hydrothermal method showedthe characteristics of better dispersion and uniform particle size. Hence, the sol-gel-hydrothermal method has certain advantages comparing to the sol-gel process.（3） The BaTiO₃particles showed some degree of aggregation prepared bysol-gel-hydrothermal method. In order to improve the dispersion of BaTiO₃powdersand inhibit the wider particle size distribution as well as large particle size caused byaggregation, the influences of three dispersants on the particle size and dispersion ofBaTiO₃particles were investigated. The experiment results indicate that anappropriate amount （0.1%） of SDBS could decrease the particle size of BaTiO₃andimprove the dispersion of particles, however, excessive amount of SDBS made the dispersion of BaTiO₃particles become worse with relatively small amounts of BaSO4.The effects of CTAB on improving the dispersion of BaTiO₃powders were notobvious, and only when the amount of CTAB reached15%, the dispersion could beimproved to some extent. An appropriate amount （5%） of PEG6000could decreasethe particle size of BaTiO₃and made the dispersion of powders get better.