Relationship Between Structure and Electric Properties of （0.99–x）BNT–xBKT–0.01KNN Near Morphotropic Phase Boundary

研究了三方、四方共存即准同型相界（morphotropic phase boundary,MPB）]附近（0.99–x）Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–0.01K0.5Na0.5NbO3（0.99–x）BNT–xBKT–0.01KNN,x=0.16～0.23]无铅压电陶瓷的电学性能与其结构之间的变化关系。X射线衍射分析表明,随着x的增大,陶瓷材料相结构由三方相转变为四方相。当x=0.20时,（111）和（200）面衍射峰均形成劈裂峰,标志着该组分的相结构由三方–四方相共同组成,形成MPB区。样品的介电温谱表明,铁电–反铁电转变温度（Td）随着x的增大而减小,但Curie点（TC）并未明显变化。电致应变（S）随着x的增大,呈现先增加后减小的趋势,并在x=0.20时得最大值0.46%,此时动态压电系数约为575 pm/V。电滞回线显示,陶瓷样品的剩余极化强度Pr和矫顽场Ec都随着x的增大而减小,分别由41.5μC/cm2降为15.2μC/cm2和由46.5kV/cm降为15.0kV/cm,并伴随着电滞回线由扁平到束腰的形状变化,呈现从铁电相特性到反铁电相特性的转变过程。

Relationship Between Structure and Electric Properties of (0.99–x)BNT–xBKT–0.01KNN Near Morphotropic Phase Boundary

A relationship between the electric properties and the structure of lead-free ceramics(0.99–x)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3– 0.01K0.5Na0.5NbO3 (0.99–x)BNT–xBKT–0.01KNN,x = 0.16–0.23] near the region where tetragonal and rhombohedral phase co-existed(morphotropic phase boundary,MPB) was investigated.The analysis by X-ray diffraction indicated the transition from rhombohedral to tetragonal phase as the BKT content x increased.The peak splits of(111) and(200) occurred simultaneously at x = 0.20,indicating the ceramic had a structure of coexistence of rhombohedral and tetragonal phases(viz.formed MPB).The results of dielectric temperature spectra showed that the ferroelectric to anti-ferroelectric transition temperature Td decreased with increasing x,while the Curie point(TC) showed slight changes.The electrostrictive strain(S) firstly increased and then decreased,giving a maxi-mum value of 0.46% at x = 0.20,which equaled to the dynamic piezoelectric coefficients of 575 pm/V.The electric hysteresis loop test exhibited that the remanent polarization Pr and coercive field Ec decreased from 41.5 μC/cm2 to 15.2 μC/cm2 and from 46.5 kV/cm to 15.0 kV/cm,respectively,with increasing x,and the loops showed a transition from ferroelectric properties to anti-ferroelectric properties.