Investigation On Flash Sintering Behavior Of Several Typical Ferroelectric Ceramics Material

With the development of modern information technology,the industrial demand of electronic ceramic materials is increasing rapidly.However,the preparation of ceramic materials usually needs to be carried out at high temperature,which consumes a lot of energy and increases the production cost.Flash sintering technology is a new electric field assisted sintering technology developed in recent years.It can realize the rapid densification of ceramic green at very low temperature.This technology injects new power into the industrial production of ceramic materials.In this paper,the flash sintering behavior of BaTiO3,Na0.5Bi0.5TiO3 and NaNbO3,which are three typical ferroelectric ceramic materials with great development prospect,is studied.On the one hand,we hope to speed up the application process of flash sintering technology,on the other hand,we hope to explore the mechanism of flash sintering technology through the flash sintering behavior of these three ceramics.In addition,the structure,micro morphology,dielectric properties and ferroelectric properties of the ceramics prepared by flash sintering were studied systematically.When the applied electric field strength is increased from 100 V/cm to 160 V/cm,the onset temperature of flash sintering is reduced from 1121? to 1052?,which shows that the flash sintering technology can greatly reduce the sintering temperature and improve the sintering efficiency.In addition,the SEM results show that the grain size of the anode and cathode regions of BaTiO3 ceramics prepared by flash sintering is significantly different,and the grain size of the anode region is larger than that of the cathode region,which leads to the higher dielectric constant of the cathode region for BaTiO3 ceramics.On this basis,the flash sintering behavior of Nb2O5 doped BaTiO3 ceramics was further studied.The results show that under the same applied electric field,with the increase of Nb2O5 doping amount,the onset temperature of BaTiO3 flash sintering decreases,which is mainly due to the increase of carrier concentration in BaTiO3 due to Nb2O5 doping.Under the action of electric field and thermal activation,the increase of carrier motion makes BaTiO3 samples easier to reach the flash sintering state at a lower furnace temperature.The flash sintering behavior of Na0.5Bi0.5TiO3 ceramics with different applied electric field was studied.When the applied electric field increased from 100 V/cm to 180 V/cm,the onset temperature of flash sintering of the samples decreased from 994? to 785?.Compared with the traditional sintering,flash sintering can effectively reduce the sintering temperature of Na0.5Bi0.5TiO3 ceramics and shorten the sintering time,thus inhibit the volatilization of Bi element in Na0.5Bi0.5TiO3.The XRD results show that the phase structure of Na0.5Bi0.5TiO3 ceramics prepared by flash sintering under different applied electric fields has not changed.In addition,the breakdown strength of Na0.5Bi0.5TiO3 ceramics is increased with the enhancing of electric field strength due to the decrease of grain size.The constant temperature flash sintering experiment of La2O3 doped NaNbO3 shows that the incubation time of flash sintering is obviously shortened with the increase of electric field strength.This is because that the increase of driving force for nucleation of stress defects under high electric field,which promotes the occurrence of flashover.When the DC electric field is 160 V/cm,the flashover incubation time of NaNbO3 is shortened from 28 s to 9 s with the increase of La2O3 doping from 0.05 to 0.1,which is caused by the increase of defect concentration in NaNbO3 ceramcis.The mechanism of nonlinear increase of conductivity and the rapid densification of samples in flash sintering are obtained by theoretical analysis.The nonlinear increase of conductivity is caused by the interaction of electric field and temperature field.In the early stage of flash sintering,due to the application of electric field for a long time,Poole Frenkel emission reduces the coulomb barrier around the local carrier,which makes the carrier migration and charge accumulation in the sample intensified.Followed by,an induction electric field is established between the sample and the anode and cathode ends of the sample.At the same time,with the increase of furnace temperature,the number of thermally activated carriers increases,which promotes the induced electric field increases.Finally,under the critical temperature of the corresponding electric field,a large number of carriers in the sample migrate under the action of the internal induced electric field,which makes the non-linear increase of the conductivity of the sample and triggering the flash sintering.The power dissipation in the sample produces uneven region because of the flash sintering.The runaway phenomenon of joule heat causes some solid particles in the sample to melt into liquid phase,and then forms a liquid film around the solid particles.Due to the surface tension,the liquid film exerts a certain force on the solid particles.At the same time,due to the appearance of liquid phase,the mass transfer mode of particles in the sample changes from solid diffusion charge to flow mass transfer,so the mass transfer speed between particles is faster,which makes the sample complete densification process in a short time.