Study On Textured And Fabrication Of BNT-based Lead-free Piezoceramics

The Bi_0.5Na_0.5TiO₃?designated as BNT?based lead-free piezoelectric ceramicsexhibit good ferroelectric properties such as high Curie temperature,remnant polarization,field induced strain,and anisotropic electromechanical coupling coefficient.Thus,the BNT ceramics have been considered as one of the most promising alternatives of lead-free piezoelectric materials to lead-based piezoelectric ceramics.It is possible that the BNT ceramics could be applied to various electronic components such as sensors,actuators,transducers,and positioning devices.This research was conducted to study the BNT-based piezoelectric ceramics,[Bi_0.5(Na₈₅?96K₁₁?96)_0.5]_?1-x?Ba_xTiO₃,x=0.03-0.07,and to understand the microstructure and property of the morphotropic phase and boundary.The effects of Hf⁴⁺B replacement of Ti⁴⁺by doping on the morphology,structure,piezoelectric,strain and dielectric properties of the material were studied systematically.Also,the texture technology of this BNT on the piezoelectric properties and performance was also evaluated.The phase composition and microstructure were characterized by X-ray diffraction?XRD?and scanning electron microscopy?SEM?.The differences of dielectric,piezoelectric and strain properties of BNT-based ceramic samples were also studied in detail as well.The conclusions drawn from the systematic studies of this research of this research are listed as follow:?1?ThecompositionofBNTpiezoelectricceramicsisbasedon[Bi_0.5(Na₈₅?96K₁₁?96)_0.5]_?1-x?Ba_xTiO₃,x=0.03-0.07.Results show that the samples exhibit the coexistence of ferroelectric tripartite phase and quadrilateral phase,and piezoelectric and dielectric properties have the characteristics of morphotropic-phase-boundary.Also,results show that the BNT-BKT-BT ternary piezoelectric ceramic exhibits a wider morphotropic-phase-boundary composition region as compared with those resulted reported previously.In addition,when x=0.05,the sample exibits much better overall performance,such as the piezoelectric coefficient d₃₃=142 pC/N,and the dielectric constant ?^T₃₃/?₀=1195.?2?The effect of B-substitution of HfO₂ on the structure and properties of(Bi_0.475Na_0.405K_0.055Li_0.015)_0.95Ba_0.05TiO₃ ceramics was studied in this research.Result show that the substitution of Hf⁴⁺to Ti⁴⁺obviously changes the phase structure and significantly influences the piezoelectric?strain and dielectric properties of the material.When the addition amount of HfO₂ is 1mol%,the negative field induced strain of the sample disappears,and the sample exhibits a higher field-induced strain.The sample could reach0.295%strain under the electric field of 6kV/mm,and the inverse piezooelectric coefficient and the dielectric constant is(d^*₃₃=490pm/v and ?^T₃₃/?₀=1408,respectively.?3?The BNT-based textured ceramics by Reactive Templated Grain Growth?RTGG?texturing technology using Na_0.5Bi_0.5TiO₃ as seed crystal were also prepared in this study.Under the heat treatment condition of 4 hours of holding time,the material with a texture of80%or more could be obtained.Compared to the domain random samples,the piezoelectric constant and field-induced strain of RTGG sample were improved by more than 50%.At1100?,BNKLBT-T exhibits much better performance than other BNT-based materials reported with d₃₃=223 pC/N and(d^*₃₃=805 pm/V.