Morphotropic Phase Transition And Electric Properties Of NBT-KBT-BT Ternary Lead-free Piezoelectric Ceramics

Sodium bismuth titanate (Na_0.5Bi_0.5TiO₃, abbreviated as NBT) is a kind offerroelectric materials with ABO3structure, which has larger remanent polarization（P_r=38μC/cm²） at room temperature and high Curie temperature（T_c=320oC）, so NBThas been considered to be one of the most promising materials and an excellentcandidate of lead-free piezoelectric ceramics because of its strong ferroelectricity.However, the Piezoelectric properties of NBT is only64pC/N because of its highcoercive field （E_c=73kV/cm）. In order to reduce the coercive field, the potassiumbismuth titanate （KBT） and barium titanate （BT） have been soluted to NBT in thispaper, and using Sol-Gel method and combustion method to prepare the power ofNBT-KBT-BT. The Relationship between the composition of the ternary system andthe phase structure electrical properties was be investigated.From the result of XRD fine scanning and electric hysteresis loop, complexphase structure was found in （1-x）[0.82NBT-0.18KBT]-xBT system with tinychange of x. The shape of electric hysteresis loop was standard when x=0.05, wherethe phase structure was tetragonal. With the increase of x, the result of XRD finescanning did not change obviously, but antiferroelectric characteristics was found inthe electric hysteresis loop when x=0.06、0.07, so the phase structure of ternarysystem ceramic was tetragonal antiferroelectric phase when x=0.06、0.07. When xdecreases to0.04, not only the double hysteresis loop was found but also thenumber of XRD peaks increased, that indicated rhombohedral and tetragonal-likephases coexist when x=0.04, and the electrical properties of the Ternary system ishighest: S=0.18%, d₃₃=540pm/V.Then, studied the （1-4x）NBT-3xKBT-xBT system and （1-2x）NBT-xKBT-xBTsystem, the results are as follows:1) the grain size of NBT-KBT-BT system is verysmall （only about1-2um） when use the Sol-Gel method and combustion method,and it was decreased slightly with the increasing of KBT and BT. In addition,fibrous structure was found at the surface of the ceramics;2) T-like phase and theR-like phase were be found in the two systems, the dielectric and piezoelectric arehigher when the components in the tetragonal-like phase.When x=0.05in（1-2x）NBT-xKBT-xBT system, where rhombohedral-like and tetragonal-like phasescoexist, the electrical properties of the Ternary system is highest:S=0.4%，d₃₃=655pm/V.The additives of La3+and Zr4+obviously influenced the phase structure and properties of the0.90NBT-0.05KBT-0.05BT ceramics. The dielectric loss ofNBT-KBT-BT ceramics reduced significantly when La3+doped. In0.90(N_0.5B_0.5)_（1-x）L_xT-0.05（K0.5B0.5）（1-x）LxT-0.05BT system, dielectric losstanδ=0.043when x=0.020, and the piezoelectric coefficient reach to411pm/V whenx=0.015. The emanent polarization of the NBT-KBT-BT ceramics increased whenZr4+doped. In0.90(N_0.5B_0.5)T_（1-x）Z_x-0.05(K_0.5B_0.5)T（1-x）Z_x-0.05BT system,2Prwasenhanced to42μC/cm²and the piezoelectric coefficient d₃₃=343pm/V when x=0.005.In addition, the grain size reduced obviously when x>0.010.