Study On Property Improvement Of NBT-based Lead-free Piezoelectric Ceramics

Bismuth Sodium Titanate Na0.5Bi0.5TiO3(abbreviated NBT) is a ferroelectric ceramicthat has the A-site complex perovskite type structure. In this paper, NBT-based ceramics withoptimized the morphotropic phase boundary compositions were prepared by the conventionalsolid state reaction. The dielectric relaxation feature, phase transition feature and materialcomposition on the role of the law of ferroelectric and piezoelectric properties beeninvestigated by analysised the structure of perovskite structure of components.The new lead-free piezoelectric materials with high piezoelectric and ferroelectric activitywere prepared.The lead-free piezoelectric ceramics NKBT-LBT and NKBBT-LBT were prepared bysolid solution with Li0.5Bi0.5TiO3into Na0.4K0.1Bi0.5TiO3and Na0.44K0.04Bi0.48Ba0.04TiO3ceramics. In the study of their composition range, the X-ray diffraction (XRD) analysisrevealed that the two sets of ceramic systems form a single perovskite structure, and themorphotropic phase boundary (MPB) between the rhombohedral and tetragonal phases ofNKBT-LBT was identified in the composition range of0.08≤x≤0.10, and the morphotropicphase boundary of NKBBT-LBT was identified in the composition range of0.06≤x≤0.12.With the increasing of LBT content，the sintering temperature and the grain size decreasd. Theferroelectric properties of the NKBT ceramics are further improved with the introduction ofthe LBT content. And the remnant polarization Princreases from7μc/cm2to15μc/cm2. Thepiezoelectric activity is enhanced with an increase in LBT content and piezoelectric constantd33reaches145pC/N at the morphotropic phase boundary.In order to further study the material properties change of NBT-based ceramics, thedense lead-free piezoelectric ceramics NKBT-NN、NKBT-KN and NKBT-LN were preparedby solid solution with NaNbO3、KNbO3and LiNbO3into NKBT-based ceramics. In the studyof their composition range, the X-ray diffraction (XRD) analysis revealed that the three sets ofceramic systems form a single perovskite structure. The grain size decrease with the increase of KN content, the diffuse phase transition characteristics is significant. The dielectric andferroelectric properties are further improved with introduce of NaNbO3component and thepiezoelectric constant was increased to d33=131pC/N. With the increasing of LiNbO3amount,the coercive field declined obviously from29.1kV/cm to19.7kV/cm. At the same time, theferroelectric–antiferroelectric transition temperature moved significant form high temperatureto low temperature and antiferroelectric-paraelectric transition peak was repressed obviously.In order to further the exploration of the relationship between the material structure andproperties of NBT-based ceramic, the the high piezoelectric activity ceramics NKBT-BF andNKBBT-BC were prepared by solid solution with BiFeO3and BiCoO3. For NKBT-BFceramics, the morphotropic phase boundary (MPB) lies in composition range of x=0.02~0.06.The sintering temperature significantly decreases of BF content. The piezoelectric constantd33increased firstly and then decreased.When x=0.06, the maximum of d33was127pC/N.For NKBT-BC ceramics, the morphotropic phase boundary (MPB) lies in a narrowcomposition range of x=0.01~0.02.The relaxation degree gradually increase with theintroduce of BC. The piezoelectric activity is enhanced with an increase in BC content andpiezoelectric constant d33reaches119pC/N at x=0.02.