Preparation Of Tetragonal Barium Titanate Nanopowders

BaTiO₃ are the main materials for the preparation of multilayer ceramic capacitors(MLCC),embedded capacitors,optical memory and electro-optic devices,because of its special dielectric,piezoelectric and ferroelectric properties.The high performance tetragonal BaTiO₃nanocrystalline powder with a diameter of less than 150 nm is the key raw material for large capacity and ultra-thin MLCC devices.It is of great significance to develop a new method for synthesize BaTiO₃nanocrystalline powder to meet the needs of miniaturized MLCC devices.In addition,BaTiO₃powder with special morphology can meet the needs of specific occasions,so that its application can be expanded,and its synthesis is a research hotspot of powder preparation in recent years.In this paper,small size tetragonal BaTiO₃powder and special morphology BaTiO₃powder such as wires and sheets were prepared by molten salt method and molten salt etching method.The main contents are as follows:1.The preparation of tetragonal BaTiO₃ powder less than 150 nm by molten salt method was studied.The results show that the BaTiO₃powder with average particle size of 122.6±40.5 nm,uniform particle size,less agglomeration,c/a of 1.0047 and tetragonal phase can be synthesized by using Ba CO₃andTiO₂as precursors,the molar ratio of Ba CO₃?Ti O₂and Na Cl is 1:1:20,and treated at 810?for 3h;When Barium titanyl oxalate was used as precursor,the molar ratio of Barium titanyl oxalate to Na Cl was 1:20,and treated at 810?for 3h,the pseudo cubic BaTiO₃powder with average particle size of 65.78±23.54 nm was obtained.The results of dielectric properties show that the dielectric constant of undoped BaTiO₃increases with the increase of sintering temperature at room temperature.The dielectric constant of ceramics prepared at 1280?is 2492.82 and the dielectric loss is 0.009.The results show that the BaTiO₃powders doped with Nb?Co?Bi?Ho?Zn and B are more compact.The dielectric constant of the doped ceramics sintered at 1220?is 2225.93,the dielectric loss is 0.015,and the Curie temperature is around 120?.The doped ceramics meet the X8R standard of MLCC dielectric materials,when the sintering temperature is in the range of 1140?1180?.And all the doped ceramics meet the MLCC dielectric material of X7R standard.2.The changes of morphology,element and phase composition of BaTiO₃nanoparticles in molten salt environment were studied.BaTiO₃nanoparticles undergo a morphological transformation in a Na Cl molten salt environment,beginning with nanoparticles then changing to nanowires and microsheets,while the composition is transformed from pure BaTiO₃into a mixture of Ba₂Ti₆O₁₃,Na₂Ti₆O₁₃and BaTiO₃.The diameter of nanowires is50?500 nm and the length is 20?150?m.The process is closely related to temperature,and also affected by the high temperature treatment time and molten salt content.It is speculated that the mechanism of nanowires formation is a dissolution-precipitation process and that the formation of the microsheets is due to the melting of the BaTiO₃nanoparticles at high temperature.3.The effect of molten salt etching on the morphology and size of BaTiO₃powder was studied.BaTiO₃powders prepared by different methods were used as precursors for molten salt etching,and the effects of reaction temperature and time on the process were studied.The morphology,particle size and particle size distribution of BaTiO₃powders prepared by sol-gel method changed greatly after etching.From the original aggregates to monodisperse tetragonal nanoparticles of 60.9±18.8 nm.However,the particle size of BaTiO₃powder prepared by solid-state method can be reduced to half of the original size after etching,and the agglomeration is weakened.But,the BaTiO₃powders prepared by oxalate precipitation method and hydrothermal method have little change after etching.