Preparation And Modification Of Tetragonal Nano Barium Titanate Powder

Barium titanate is one of the most widely used ferroelectric materials in the field of electronic ceramics and is known as the"pillar of the electronic ceramics industry".The development trend of MLCC with high capacity,high reliability,and miniaturization puts forward higher requirements for the particle size,tetragonal phase content,and dispersion of barium titanate powder.The hydrothermal method is a common method for preparing highly dispersed and small particle-size barium titanate powder.However,the prepared powder has low tetragonality and many surface defects and is also subject to its high equipment cost and preparation cost.The solid-state method has the advantages of a simple process,low cost,and can realize the preparation of pure tetragonal barium titanate powder with few defects.However,its large particle size and agglomeration seriously fail to meet the needs of high reliability and miniaturization MLCC.Therefore,how to realize the low-cost preparation of high tetragonal phase,small particle size and high dispersion barium titanate nano-powders is still the focus and hotspot in the field of electronic information materials and components.Therefore,in this paper,the particle size and dispersion of barium titanate powder prepared by solid phase method were studied according to the particle size and reactivity of barium carbonate powder.The specific research contents are as follows:（1）Using Ba（OH）₂·8H₂O and dry ice as raw materials,the effect of the preparation process on the particle size of barium carbonate was discussed.The preparation of 180nm short rod-like Ba CO₃ powder was realized under optimal conditions.The structure,morphology,and properties of the prepared tetragonal barium titanate powder were verified by using it as the precursor material.The results show that the prepared barium titanate is 400 nm uniformly dispersed pure tetragonal phase（c/a=1.01）barium titanate powder.Thanks to the high tetragonality,uniformity,and dispersibility of the powder,the dielectric constant and dielectric loss of the prepared ceramics at room temperature are4885 and 0.0189,respectively,which are better than those of barium titanate ceramics synthesized by commercial Ba CO₃（Hubei Tianci）with D₅₀=0.5μm（εr=3935,tanθ=0.0218）.（2）Using C₄H₆O₆,Ba（OH）₂·8H₂O,and H₂TiO₃ as raw materials,the thermal decomposition behavior and crystallization mechanism of precursor materials in the calcination process were investigated.The results show that the prepared barium tartrate nano-powders can be decomposed into Ba CO₃ particles with a particle size of 40 nm at450°C.The ultrafine particle size of Ba CO₃ has ultra-high decomposition activity and can be decomposed into Ba O at only 550°C.At the same time,due to the unique chemical activity of dihydroxyl and dicarboxylic groups,the precursor obtained by decomposition at 450°C is an ideal structure in which nano-Ba CO₃ is uniformly coated on the surface of TiO₂.Such a structure not only improves the reactivity of the precursor but also reduces the diffusion distance of Ba²⁺during nucleation.Therefore,the precursor only needs to be calcined at 650°C（250°C lower than the traditional solid-state method）to obtain 50 nm cubic barium titanate powder,and then calcined at 1050°C to obtain an average particle size of 248 nm,high tetragonal phase（c/a=1.0096）uniformly dispersed barium titanate powder.The barium titanate ceramics prepared by the above powders have excellent dielectric properties:εr=5980,tanθ=0.0139.（3）Based on the above research results,the paper also carried out the preparation of calcium-doped nano-barium titanate(Ba_1-xCa_xTiO₃)by tartaric acid-assisted method and discussed the key parameters in the synthesis process such as solution p H,calcium doping amount on the structure,morphology,and properties of barium calcium titanate powder.The results show that:1.The average particle size of Ba_1-xCa_xTiO₃ powders increases first and then decreases with the increase of Ca²⁺doping amount.When x=0.03,the average particle size of the obtained powders is 450 nm,and when x=0.15,the average particle size decreases to 120 nm.This is because when the Ca²⁺content of the system increases,Ca²⁺tends to replace B-site,which inhibits grain growth.The introduction of calcium ions will make the Curie peak move to the high temperature region and bring the negative effect of dielectric constant reduction.When x=0.09,the Curie peak of the ceramic is located at 138°C,and the dielectric constant at room temperature is 3067.