Study On The Effect Of Antiferroelectric Components On The Microstructure And Electrical Properties Of BNT Based Lead-free Ceramics

Na_0.5Bi_0.5Ti O₃?BNT?based ceramics have high Curie temperature,good ferroelectric and antiferroelectric properties.It is one of the strong competitors to replace lead-based ceramics.BNT-based ceramics are worthy of in-depth research and development in the fields of energy storage and strain.Antiferroelectrics have a strong resistance to breakdown,large storage density and high electrostriction.In order to increase the saturation polarization(P_max)of the BNT-based ceramics and enhance its breakdown strength to obtain excellent electrical properties.This paper mainly studies the effects of three antiferroelectric components,Cs₂Nb₄O₁₁?CN?,Sr_0.7Ca_0.3Ti O₃?CST?and Ag Ta_0.15Nb_0.85O₃?ATN?,on the structure and electrical properties of lead-free ceramics with BNT solid solution of Bi_0.5K_0.5O₃?BKT?or Ba Ti O₃?BT?as the second component.?1?The effect of CN doping on the structure and electrical properties of 0.82BNT-0.18BKT-x CN?BNKT-x CN?ceramics were studied.Research indicates that under different CN doping contents.When a small amount of CN is doped,the BNKT-x CN ceramic is a standard perovskite structure.With the increase of CN doping content,the XRD pattern shows a split peak of the second phase with a tungsten bronze structure,but the main phase is still perovskite structure.SEM images show that CN phase can refine grains with increasing doping content.When x=0.03,generate large grains related to the tungsten bronze structure on the surface of small ceramic grains.The x=0.005 doping can achieve the anti-ferroelectric property of BNKT ceramics at room temperature.Further appropriate doping can pinch the ferroelectric curve,improve the saturation polarization,and increase the energy storage density.The x=0.02 obtains the optimal energy storage density,and 1.0 J/cm³ is obtained under an electric field of 100k V/cm.But excessive doping will cause long-range order to be destroyed and weaken ferroelectricity.The maximum electrostriction of 0.48%is obtained at x=0.005.The temperature-dependent dielectric spectrum further confirms that the main phase of BNKT-x CN ceramics is a pseudocubic phase.?2?The effect of CN doping on the structure and electrical properties of 0.94BNT-0.06BT-x CN?BNBT-x CN?ceramics were studied.Research indicates that the main phase of BNBT-x CN ceramics is still perovskite structure under different doping content of CN.Due to the increase of CN doping,CS₂Nb₄O₁₁ phase was formed.SEM shows that the microstructure is dense packing,and the rod-shaped grains are formed under low doping content.After increasing the doping content,the rod-shaped grains disappear and large block grains are formed.With the increase of doping content,the ferroelectric property of BNBT-x CN ceramics is gradually weakened and has relaxation characteristics.At x=0.01,the energy storage density is 0.70 J/cm³and the energy storage efficiency is 44.83%.The dielectric spectrum verified that the main phase is a pseudocubic phase.?3?The effect of CST doping on the structure and electrical properties of 0.82BNT-0.18BKT-x CST?BNKT-x CST?ceramics were studied.Research indicates that the CST doped BNKT ceramics are standard perovskite structure,under low doping,the trigonal phase and tetragonal phase coexist,and as the doping content increases,the main phase becomes a pseudocubic phase.Irregular grains were observed through SEM,which may be caused by the sintering temperature set too high relative to the composition point during the sintering process,or because the holding time during sintering exceeds the required amount too much.When the CST doping content is x=0.15,the maximum saturation electro-induced strain of 0.34%is obtained at 60 k V/cm,and its inverse piezoelectric coefficient d^*₃₃=567pm/V.When the doping content of CST x=0.30,the maximum saturated electric strain of 0.60%was obtained under the electric field of 100 k V/cm,and its reverse piezoelectric coefficient d^*₃₃=600 pm/V;At the composition point of x=0.25,under the electric field intensity of 100 k V/cm,the maximum energy storage density of 1.01 J/cm³ is obtained,and the energy storage efficiency is 56.2%.From the dielectric spectrum,with the increase of CST doping content,the depolarization temperature T_d decrease and below room temperature,T_m=280?does not change,but the dielectric constant decreases.?4?The effect of CST on the structure and electrical properties of 0.94BNT-0.06BT-x CST?BNBT-x CST?ceramics was studied.It is found that BNBT ceramic doped with CST shows the standard perovskite structure,and the main phase of the ceramic is a pseudocubic phase.SEM images show that with the increase of CST doping content,the grain size of BNBT-x CST ceramics decreases significantly and then gradually increases.The x=0.24 achieves good energy storage property,the maximum energy storage density is 0.96 J/cm³ under 90 k V/cm.The maximum electrostriction of 0.66%is obtained at x=0.16,and the reverse piezoelectric coefficient is d^*₃₃=733pm/V.Dielectric temperature spectrum analysis shows that with the increase of temperature,there is a strong frequency dispersion between T_P and T_m,and the frequency dispersion disappears when it reaches T_m.The T_m peak gradually moves towards the low-temperature direction with the increase of doping content,and the doping of CST has little effect on the T_m peaks.?5?The effect of ATN doping on the structure and electrical properties of 0.82BNT-0.18BKT-x ATN?BNKT-x ATN?ceramics were studied.Research indicates that when the doping content of ATN is low,BNT-BKT ceramics illustrate the standard perovskite structure.With the increase of the content of ATN,the heterophase of Nb rich phase is formed.SEM images show that as the ATN doping content increases,the grains gradually become smaller and rod-shaped grains are generated.When x=0.15,large size grains are formed on ceramic surface.Appropriate doping can pinch the ferroelectric curve and improve the saturation polarization,but excessive doping will cause the long-range order to be destroyed and the ferroelectricity will be weakened.Due to the influence of cation volatilization during the sintering process,the electro-induced strain has obvious asymmetry.When the ATN doping content x=0.05,the maximum electro-induced strain of 0.30%is obtained.?6?The effect of ATN doping on the structure and electrical properties of 0.94BNT-0.06BT-x ATN?BNBT-x ATN?ceramics were studied.Research indicates that under different ATN doping contents,the main phase of BNBT-x ATN ceramics is perovskite structure.Due to the volatilization of potassium and sodium ions during high-temperature sintering,niobium-rich impurity phases are easily formed.The microstructure of BNBT-x ATN ceramics with different doping contents is compact.With the increase of doping content,rod-shaped grains are formed;BNBT-x ATN ceramics have good ferroelectric properties at different doping contents.Due to the influence of sintering conditions,some ions volatilization leads to obvious asymmetry of electrostriction,and the maximum strain of BNBT-x ATN ceramics is 0.49%at x=0.01.