Preparation And Properties Of Samarium-Doped Barium Titanate By High Gravity Co-Precipitation

Barium titanate is a typical chalcogenide structure crystal with high dielectric constant,which is an efficient raw material for making thermistors,electronic ceramics,multilayer ceramic capacitors（MLCC）and other components.With the development of the miniaturization of components,the preparation of barium titanate powder has gradually become one of the current research hotspots.The preparation of barium titanate nanoceramics has three main parts,preparation of raw material of barium titanate nano powder,pressurized molding,and high temperature sintering.Among them,the preparation of raw materials is extremely important,the preparation of nanoceramics with excellent performance requires barium titanate nano powders with small particle size,narrow particle size distribution and uniform distribution.In this paper,barium titanate nano precursors were prepared by liquid-phase co-precipitation method using Ba Cl₂,Ti Cl₄ and Sm Cl₃ as raw materials and NH₄HCO₃ and NH₃·H₂O as precipitants in a stirred reactor and an impinging stream-rotating packed bed（IS-RPB）,respectively.The obtained powers were calcined in a resistance and microwave tube furnace.The effect of reaction temperature,calcination temperature,aging time,feed rate and high gravity factor on the particle size and its distribution and dielectric properties of barium titanate powder were explored by single factor.It is dedicated to solving the problems of large particle size and unstable dielectric properties of barium titanate powders prepared by traditional precipitation reaction due to serious agglomeration.Firstly,the preparation of barium titanate nano powders was studied in a stirring reactor.The results showed that with the increase of reaction temperature,calcination temperature,and aging time,the particle size of barium titanate powder tended to decrease first and then increase;with the increase of holding time,the particle size of barium titanate powder showed a gradual decrease trend.With the increase of reaction temperature,calcination temperature and aging time,the particle size distribution becomes narrower and then wider;with the increase of holding time,the particle size distribution becomes narrower.The optimal reaction conditions were the concentration of titanium chloride and barium chloride were 0.5 mol/L,the addition of dispersant hydroxyethyl cellulose,the reaction temperature was 60°C,the p H of the reaction process was maintained≥9,the aging time was 120 min,the calcination temperature was950°C,and the calcination time was 2 h.The average particle size of the prepared powder was230 nm,and the particle size distribution was in the range of 100-310 nm,and Presence of significant clustering.Then the barium titanate nano powders were prepared by using IS-RPB reactor,and the effects of impact initial velocity and high gravity factor on the particle size and particle size distribution of barium titanate powders were investigated,and it was found that the particle size of barium titanate nano powders tended to decrease with the increase of impact initial velocity and high gravity factor.The best reaction conditions:the average particle size of the prepared barium titanate nano powders was 132 nm at an initial impact velocity of 21.24 m/s and a high gravity factor of 45.00,and the particle size distribution was between 95-150 nm.Compared with the barium titanate nano powder particles have smaller particle size,more uniform particle size distribution and no obvious agglomeration.It is shown that the IS-RPB reactor has a better micro-mixing effect and can form more small nuclei with the smaller particle sizes of barium titanate when using the same concentration as well as the volume ratio of raw material.However,due to the size effect,the small particle size of barium titanate will make the dielectric constant decrease,which is not conducive to subsequent industrial applications.Therefore,in this paper,the rare earth element Sm³⁺-doped Ba Ti O₃ was used to improve its dielectric properties.In order to investigate the dielectric properties of Sm³⁺-doped Ba Ti O₃ ceramics prepared by IS-RPB,the nano-barium titanate ceramics were prepared by resistive and microwave tube calciners,respectively,and the nano-barium titanate ceramics prepared by obtaining powders under different preparation conditions were compared,and the effects of molding pressure and sintering temperature on the densities and dielectric properties of the nano-barium titanate ceramics were also investigated.The results showed that the 0.3%Sm³⁺-doped Ba Ti O₃ powder was prepared by IS-RPB The smallest particle size of 86 nm was achieved,calcination temperature of 950°C and holding time of 2 h.And sintered in a microwave muffle furnace at a sintering temperature of 1150°C,the holding time is two hours,and a molding pressure of 12MPa,and good performance ceramics were obtained with a grain size of 124 nm,a dense density of 6.54 g/cm³,a dielectric constant of 3740,and a dielectric loss of 0.043.With the increase of sintering temperature and molding pressure,the bulk density of nano-barium titanate ceramics increases,the porosity decreases,and the dielectric properties are high;the sintering temperature of barium titanate ceramics sintered in microwave muffle furnace is 150℃lower than that in resistance furnace,which effectively overcomes the problem of high sintering temperature in resistance furnace,and the ceramics sintered with higher density and better dielectric properties than those sintered in resistance rate.The synthesis shows that the preparation of barium titanate nano-powders by IS-RPB combined with microwave muffle furnace has small particle size and narrow particle size distribution;the dense and dielectric properties of ceramics are better,which can easily meet the application requirements of high-tech fields and realize industrial production,the research results can provide new ideas and basic data for subsequent industrial production.