Preparation And Properties Of Highly Dispersed Nano-sized Barium Titanate Powders By Hydrothermal Method

Barium titanate(BaTiO₃,BT for short)is the most widely used ferroelectric ceramic material with excellent physical properties,known as"the industrial pillar of electronic ceramics".With the continuous development of electronic equipment to miniaturization and intelligence,the size of MLCC gradually decreases,and the thickness of medium layer decreases.However,the thin medium layer puts forward higher requirements for the particle size,tetragonal phase and dispersiveness of barium titanate powder.In this paper,the hydrothermal process of preparing high performance nano-sized barium titanate powder was studied.The physical and chemical properties of the samples were characterized and analyzed by XRD,FT-IR,PSD,SEM and other characterization methods.The main research work and achievements are as follows:(1)Barium chloride and titanium tetrachloride titanium barium source source,respectively,potassium hydroxide as the mineralizer,PVP(polyethylene pyrazole complex alkanes,molecular weight 10000)as dispersing agent,was prepared using atmospheric pressure hot water out of the highly dispersed cubic phase nano barium titanate powder,this paper discusses the different reaction conditions,such as temperature and the ratio of raw material barium,titanium,PVP content on the influence of the reaction products.The results show that the atmospheric pressure hot water preparation of barium titanate powder,granular crystal structure are cubic structure,when the concentration of titanium source is0.2 mol/L,barium,titanium mole ratio was 1.3:1,and set in the reaction temperature of90?,mineralizer KOH amount to 2 mol/L,the reaction time is 3 h,surfactant PVP concentration of 40 g/L,can obtain the average size of 80 nm highly dispersed cubic phase barium titanate powder.(2)The effects of fluid calcination temperature and thermosetting time on barium titanate crystal transformation were explored.The results showed that the powders were transformed from cubic phase to tetragonal phase under the condition of holding at 975?for 5 h,and the c/a was 1.009.Thanks to the introduction of PVP surfactant,the tetragonal Bt powder has good dispersibility and morphology uniformity,and the average particle size is 230 nm.Combined with FT-IR and XRD results,the decomposition of BaCO₃ in Bt powder under these conditions,the main crystal phase of the powder is tetragonal.(3)The influence mechanism of the structure and morphology of barium titanate powder under the condition of hydrothermal crystal transformation was investigated by using hydrothermal powder as raw material.Nano barium titanate powder with an average particle size of 150 nm was obtained by using the reaction medium of barium ion concentration 0.05 mol/L,KOH concentration 1 mol/L and TEA(triethanolamine)0.64mol/L at 220?for 16 h.Thanks to the introduction of TEA additive and KOH mineralizer,the crystallization of the powder was improved and the tetragonal phase transformation of part of the structure was realized.The ceramics were prepared from the powder and the dielectric properties of the ceramics were investigated.Under the sintering conditions of5?/min heating rate,600?for 4 h,then rising to 1250?for 3 h,dense barium titanate ceramics with an average grain size of about 1?m were prepared.The ceramics exhibited good dielectric properties(the dielectric constant reached 3410 at room temperature,and the dielectric loss was only about 0.8%),which met the requirements of MLCC for dielectric properties.