Preparation,Microstructure And Piezoelectric Properties Of BaTiO₃-based Ceramics

Piezoelectric ceramics as a type of functional materials which can realize the mutual transformation between mechanical energy and electrical energy are widely used in manufacturing sensors,actuators,ultrasonic transducers and other electronic components.The BaTiO3 ceramics were historically the first polycrystalline material found to exhibit piezoelectricity after being poled under an external electrical field,and had been once well used as a piezoelectric material before Pb(Zr,Ti)O3 ceramics(often abbreviated as,PZT ceramics)appeared.However,for quite a long time,BaTiO3-based ceramics showed only relatively low piezoelectricity(d33 = 190 pC/N).Nevertheless,a number of researchers reported in recent years that they have successfully prepared pure BaTiO3 and BaTiO3-related piezoelectric ceramics with very high d33 values comparable to those values of the PZT ceramics.The results indicate that BaTiO3-based ceramic materials have great prospects for development.Industrial production of BaTiO3-based ceramics is usually made through solid-state reaction route.The choice of raw materials is the basis of ceramic preparation.The piezoelectric properties of ceramic samples prepared by different raw material may change greatly.Different treatment of raw materials can also largely affect the uniformity and particle size of the final ceramic powder,and subsuequently affect the microstructure and piezoelectric properties of obtained BaTiO3-based ceramics.In this paper,we studied the effects of raw materials and pretreatment of raw materials on the preparation and piezoelectric properties of BaTiO3-based ceramics.The main results are as follows:(1)Influences of TiO2 raw materials(specifically,TiO2-01 and TiO2-07 powders)on the physical properties of resultant BaTiO3 ceramics were instestigated.BaTiO3 ceramics with high piezoelectric properties were obtained under the sintering temperature condition of 1220℃,and their d33 values were 404 pC/N and 414 pC/N,respectively.The results show that the grain size effect of BaTiO3 ceramics prepared by the two kinds of TiO2 raw materials are consistent.When the grain size is larger than 1 μm,the piezoelectric coefficient d33 increases as the grain size increases.The change trends of phase transition point for both kinds of BaTiO3 ceramics are the same.When the grain size increases,the orthorhombic-tetragonal transition temperature TO-T decrease,and the curie temperature TC shifts to a higher value.By comparison,the BaTiO3 ceramics prepared from TiO2-01 are dense,the dielectric loss is lower,and the repeatability is better.2)Effect of raw material pretreatment on properties of BaTiO3 piezoelectric ceramics were investigated.BaTiO3 ceramics were prepared by pretreated BaCO3 powder or pretreated TiO2 powder,then physical properties of the resultant ceramics,including piezoelectric properties,dielectric properties,ferroelectric properties and microstructure were examined.Our study showed that an additional ball-milling treatment of BaCO3 powder before being mixed with TiO2 powder can remarkably reduce the size of the rod-like particles,which is an effective mean to get good-quality BaTiO3 fine powder.In such a way,we fabricated a series of small-grained dense BaTiO3 ceramics with significantly high piezoelectric coefficient d33.BaCO3 powder usually consists of large rod-shaped particles,which can not be easily broken up into fine ones when ball-milled together with TiO2 powder.This may lead to chemical compositional non-uniformity and large particle sizes of the subsequently synthesized BaTiO3 powder,and may eventually affect the microstructure and the piezoelectric properties of resultant BaTiO3 ceramics.The BaTiO3 ceramics were prepared with treated BaCO3 powders that have been ball-milled for different time before mixing with raw Ti02 powder.A much enhanced d33 value of 470 pC/N was achieved in comparison to the previous maximum one of 410 pC/N for those BaTiO3 ceramics formed through ordinary ceramic procedure.However,when TiO2-01 powder was pre-milled 3 h,the result was not ideal.The d33 value of obtained BaTiO3 only reached 190 pC/N,and hysteresis loop also appeared the contraction phenomenon.3)Effect of different TiO2 raw material and BaCO3 pretreatment on properties of BCZT piezoelectric ceramics were investigated.A pretreatment of BaCO3 powder before batching could make the particle size of BCZT ceramic powder more uniform but the average particle size was larger.When sintered at the same temperature,the resultant BCZT ceramic prepared from pre-milled BaCO3 powder shows smaller grain sizes.When TiO2-01 powder was used as raw material,a pretreatment of BaCO3 powder could greatly increase the d33 from 540 pC/N to 640 pC/N;however,when TiO2-07 powder was used as raw material,a pretreatment of BaCO3 powder could reduce the d33,reduced from 600 pC/N to 500 pC/N.