Study On Preparation Of Submicron Barium Titanate Powder By Solid State Method

Barium titanate（BaTiO₃）is often used to prepare ceramic capacitors with excellent dielectric properties.The size,capacitance and performance of the capacitor are directly determined by the particle size,uniformity and reliability of the BaTiO₃powder.Therefore,in order to obtain high performance ceramic capacitors,it is necessary to prepare the BaTiO₃powder with fine particle size and excellent performance.The preparation of BaTiO₃powder by solid state reaction is the most commonly used method in industrial production.However,due to the high calcination temperature,BaTiO₃powder with small particle size is difficult to be synthesized by solid state reaction.In order to reduce the particle size of BaTiO₃powder while ensuring a high tetragonality,the solid state reaction preparation process must be improved.In this paper,BaTiO₃powders were prepared by solid state reaction and the raw materials are BaCO₃and TiO₂.The effects of TiO₂species,BaCO₃and TiO₂particle size,and dispersant on the particle size and tetragonality of BaTiO₃powders were investigated by XRD,SEM,TG-DSC and XPS.Doped barium titanate ceramics were sintered by using BaTiO₃powder which is synthesized by improved preparation process,and the dielectric properties of barium titanate ceramics were improved by doping modification.The research contents and conclusions are as follows:（1）Effect of TiO₂raw materials on particle size and tetragonality of BaTiO₃powders.BaTiO₃powders were obtained by solid state reaction with BaCO₃powder and different TiO₂raw materials.And the different TiO₂raw materials include anatase TiO₂,90%rutile+10%anatase TiO₂and rutile TiO₂.The results show that:1)High tetragonal BaTiO₃powder is more easily prepared by rutile-rich TiO₂raw materials,and BaTiO₃powder with tetragonality greater than 1.0086 can be obtained at 1000°C.2)The kinetic results of three TiO₂raw materials show that anatase phase TiO₂raw materials have the fastest reaction rate.The reaction activation energies for the synthesis of BaTiO₃from anatase TiO₂,90%rutile+10%anatase,and rutile TiO₂raw materials are 283k J/mol,333k J/mol,and251k J/mol,respectively.（2）Effect of raw material particle size on the particle size and tetragonality of BaTiO₃powder.TiO₂and BaCO₃powders with different particle sizes were obtained by different ball milling,and TiO₂refers to 90%rutile+10%anatase phase.BaTiO₃powders were prepared by TiO₂and BaCO₃with different particle sizes.The results show that:1)The particle size of TiO₂and BaCO₃raw materials decreases,resulting in the decrease of BaTiO₃powder synthesis temperature,particle size and tetragonality.The two-step calcination is beneficial to improve the tetragonality of BaTiO₃powder,and the particle size will not grow too large.2)If the particle size difference between TiO₂and BaCO₃is too large,pure BaTiO₃powder cannot be prepared.（3）Stirring ball milling is beneficial to improve the solid reaction diffusion coefficient of TiO₂and BaCO₃,and accelerate the synthesis reaction of BaTiO₃.（3）Effect of dispersant on particle size and tetragonality of BaTiO₃powders.Glycine,glutamic acid,citric acid and triethanolamine were added as dispersants to improve the mixing uniformity of 90%rutile+10%anatase TiO₂and BaCO₃.The results showed that:1)The addition of dispersant increases the tetragonality of BaTiO₃powder,and the effect of glycine and glutamic acid is the best.XPS results show that glycine and glutamic acid are more conducive to the synthesis reaction,because the O1s binding energy difference between BaCO₃and TiO₂is reduced.2)The BaTiO₃particles are separated by the combustion products of glycine and glutamic acid,which is beneficial to hinder the growth of BaTiO₃particles.（4）The dielectric properties of barium titanate ceramics were prepared by improving the synthesis process of BaTiO₃powder.1)After improving the synthesis,BaTiO₃powder was synthesized with 90%rutile+10%anatase TiO₂as raw materials,and then the ceramics were sintered with BaTiO₃powder.Compared with the ceramics sintered by commercial powders,the grain size of the ceramics prepared by the synthesized powders is smaller,and the grain size is about 1μm.In the temperature range of-55～130°C,the TCC decreases from-28%～91%to-22%～70%.2)The dielectric temperature stability of the ceramics was improved by doping metal oxides with BaTiO₃powder.The TCC of the ceramics was less than±15%in the temperature range of-55～130℃.The dielectric constants at Curie point and room temperature were 3313 and 3171,respectively.The dielectric loss was less than 1.5%,the dielectric prooetties met the requirements of X7R.