Preparation And Electrical Properties Of Bi_0.5Na_0.5TiO₃-based Ceramics

Piezoelectric ceramics are essential to the electronics industry.For a long time,lead-based ceramics?Pb?Zr,Ti?O₃,PZT?have been dominating the main market of industrial applications,however,toxic lead will cause harm to the environment during the production and use process.With the increasing awareness of ecological environment protection,the development of high-performance lead-free ceramics materials has become an important issue.Among the lead-free ceramic systems,Bi_0.5Na_0.5Ti O₃?BNT?-based ceramics family is one of the most important candidates.Moreover,its relaxation characteristics extend its application to the dielectric energy storage field.Up to now,great progress has been achieved on BNT-based ceramics.Briefly,in the field of piezoelectric ceramics:researchers have mixed BNT and other perovskite oxides with different phase structures to form a morphotropic phase boundary?MPB?solid solutions.In the field of energy storage ceramics:researchers have improved the energy storage performance of BNT-based relaxation ferroelectric ceramics by ionic doping and substituting.Under such research background,this paper has mainly carried out the following work:First,Zn O was introduced into 0.82[0.94Bi_0.5Na_0.5Ti O₃-0.06Ba Ti O₃]-0.18K_0.5Na_0.5Nb O₃?BNT-BT-KNN?to form 0-3 type composite ceramics,BNT-BT-KNN:x Zn O?x=0,0.10,0.20,0.30,0.40?.X-ray diffraction?XRD?and scanning electron microscope?SEM?investigations confirm that the BNT-BT-KNN:x Zn O ceramics consist of two coexisted phases.The breakdown electric field E_B of ceramics increases with increasing Zn O content.For x=0 and x=0.40 samples,the maximum recoverable energy storage density is 0.74 J/cm³ and 1.03 J/cm³ while the maximum energy storage efficiency is 86.7%and 72.7%under the electric field of 9.0 k V/mm and14.0 k V/mm,respectively.The recoverable energy storage density and efficiency of the composite vary less than 2.5%from 25°C to 125°C,which indicates temperature-insensitive energy storage performance.These experimental results provide an alternative way to improve energy storage performance of relaxor ferroelectrics.Second solid solution ferroelectric ceramics of 0.8Bi_0.5Na_0.5Ti O₃-?0.2-x?Bi_0.5K_0.5Ti O₃-x Bi(Zn_0.5Ti_0.5)O₃,0.8NBT-?0.2-x?KBT-x BZT with?x=0,0.01,0.02,0.03,0.04,0.05?,were prepared and investigated.XRD results show that all samples persist rhombohedral-tetragonal morphotropic phase boundary?MPB?structure at room temperature,i.e.,the introduction of BZT does not deviate MPB.SEM results show that the average grain size of the samples gradually increases with the increase of x.Ferroelectric and piezoelectric tests show that the ferroelectricity and piezoelectricity of the sample are enhanced first and then weakened as x increases.The sample of x=0.02 has the optimal electrical property with remnant polarization,bipolar total strain,piezoelectric constant of 26.5mC/cm²,0.30%,121 p C/N respectively.And the depolarization temperature is increased from 93°C for x=0 to 135°C for x=0.05based on dielectric measurement.Piezoresponse force microscopy?PFM?investigation reveals that the domain structure transforms from labyrinthian domain for x=0 to coexistence of nanodomain and labyrinthian domain for x=0.02,end up with large amount of nanodomain?x=0.04?.Our work confirms that domain engineering is an alternative method to develop high performance piezoelectric materials.