Studies On The Phase Structure And Electrical Properties Of BaTiO₃–Bi_0.5Na_0.5TiO₃lead-free Piezoceramics

With the improvement of people’s consciousness of environmentalprotection, developing lead-free piezoelectric ceramics has become aninevitable trend. Lead-free piezoelectric ceramics of BaTiO₃（BT） andBi0.5Na0.5TiO3（BNT） are generally thought as the most potentialmaterials for replacing lead-based ceramics, which with highpiezoelectric properties and ferroelectric properties. Pure BT ceramicsowns a mediate piezoelectric properties, however, it has a low Curietemperature （Tc=120℃）. The introduction of BNT into BT canincrease the Tcof BaTiO₃–Bi0.5Na0.5TiO3（BT–BNT） system, but whichwill bring down piezoelectric properties. Series of BT–BNT lead-freepiezoelectric ceramics are prepared by traditional solid state reactionmethod in this paper. The microstructure, electric properties andtemperature characteristic were investigated of LiNbO3introducinginto BNBT6ceramics. The phase structure, piezoelectric andferroelectric properties of BaZrO₃（BZ） into （0.8-y）BT–0.2BNT–yBZceramics and different BNT to （0.97-x）BT–xBNT–0.03BZ ceramicswere investigated. Through the above work, the following results wereobtained:（1） Samples of0.06BT （0.94-x）BNT xLiNbO₃（BNBT6–xLN）ceramics are all perovskite structure of rhombohedral and tetragonalphase coexistence. When x≥0.025, he electric hysteresis loops appeardeformation, presenting a characteristic of double hysteresis loop. Withincreasing x, both the dielectric constant （εr） and dielectric loss （tanδ）increase gradually. The depolarization temperature Tdis shifted toward lowertemperatures. The introduction of LiNbO3increases the piezoelectricconstant d33first and then decreasing. When x=0.02, d33gets amaximum value of150pC/N, with kp=27%, Pr=34.1μC/cm2， Ec=28.8kV/cm， Td=68℃. （2） The researching of （0.98-y） BT–0.2BNT–yBZ ceramics foundthat: when y≤0.05, Zr can go into the BT-BNT lattice and form puresolid solution. With increasing y, when y=0.08, the second phase（BaZrO₃） was found. A morphotropic phase boundary （MPB） betweentetragonal and pseudo-cubic phases exists at x=0.03–0.04. The optimalpiezoelectric coefficient d33=71⁷2pC/N, with kp=15.4%, εr=661,Pr=18.5μC/cm2, Ec=34.1kV/cm.（3） Furthermore, a relaxor behavior is induced and the tetragonal–cubicphase transition shifts towards lower temperatures after the addition of BZ.When y=0.08, dispersion degree γ value is1.89. The Tcof ceramicsshift to low temperatures with increasing y. When x=0.03, Tcdecreases to150℃.（4） For the （1-x） BT–xBNT–0.03BZ ceramics, all of the samplesare pure perovskite phase with tetragonal phase. With the increasing ofthe content of BNT, the densites of ceramics are improved, and therelative densities can reach as high as97.4%. The d33of ceramics alsoincrease with the increasing x.（5） Mn doping on0.77BT–0.2BNT–0.03BZ ceramics show thatthe piezoelectric properties decrease gradually with increasing Mn, butthe mechanical quality factor Qmof samples increase gradually with theincreasing Mn. The Qmobtains the maximum value of220at x=0.8%.The densities of the ceramics also can be improved.