| In recent years, the environmental friendly high performance lead-free piezoceramics have become a research hotspot and attracted a wide spread attention. In this paper,(K,Na)NbO3-based (abbreviated as KNN-based) lead-free piezoceramics were modified with second phases. Microstructure and electric properties were investigated. Meanwhile, The effect of B2O3-CuO-BaO-MnO2(abbreviated as BCBM) frit contents on sintering characteristics, crystal structure, microstructures and electric properties were systematically studied.(K0.49Na0.51)0.94Li0.06Nb0.94SbxTa0.06-xO3(KNNLSxT1-x,x=0.00-0.06mol) lead-free piezoelectric ceramics were prepared by the solid state reaction method. The effect of Sb doping amount on the crystal structure and piezoelectric properties were investigated systematically. XRD results indicated that the crystal structure of the ceramics changes from an orthorhombic phase to a tetragonal one with the increasing of Sb doping amount, and the polymorphic phase transition of orthorhombic to tetragonal phases was observed when x=0.04-0.05. The optimal piezoelectric properties can be obtained when the composition of x=0.04. The piezoelectric constant d33=258pC/N, planar electromechanical coupling coefficient kp=54%, mechanical quality factor Qm=61and relatively high Curie temperature Tc=405℃. Due to its relatively high d33and kp, this lead-free piezoceramics shows good prospective application.Then, in order to get the higher performance lead-free piezoelectric ceramics, BaZrO3was further introduced as the second component. The high performance Lead-free piezoelectric ceramics of (K0.45+xNa0.55-x)0.98Li0.02(Nb0.77Ta0.18Sb0.05)O3-yBaZrO3(x=0,0.04; y=0-0.02mol) were prepared and studied. The optimal piezoelectric properties were obtained when x=0.04and the powders calcined at850℃. Results indicated that the K/Na value deviated from0.5/0.5may improve the performance. The dielectric properties were improved by the substitution of BaZrO3. The crystal structure of the ceramics changes from orthorhombic phase to tetragonal phase with the increasing of BaZrO3substitution amount, and the coexistence of orthorhombic-tetragonal phases are observed when y=0.005～0.008. The optimized piezoelectric properties can be obtained for the ceramics with x=0.005as follows:d33=372pC/N, kp=47.2%,εT33/ε0=1470, tanδ=0.021, Qm=86, remanent polarization Pr=18.15μC·cm-2and coercive field Ec=1.1kV/mm.The structure and electric properties of the lead-free piezoceramics (1-x)(K0.49Na0.51)0.98Li0.02(Nb0.77Ta0.18Sb0.05)O3-x(Ba0.85Ca0.15)(Ti0.9Zr0.1)O3[(1-x)NKNSLT-xBCZT, x=0～0.02] were investigated systematically. Results indicated that the introduction of BCZT had improved the sintering temperature and inhibited the grain growth to some extent. The d33and kp firstly increased and then decreased with the increasing of BCZT doping amount. The optimized piezoelectric properties can be obtained for the ceramics with x=0.01as follows:d33=335pC/N, kp=44.7%. On the contrary, the Qm firstly decreased and then increased with the increasing of BCZT doping amount. Tc, as well as the orthorhombic-tetragonal phases transformation temperature To-T decreased gradually when the doping content increases.Finally, the effect of the BCBM frit content on the phase structure, microstructure and electrical properties of (K0.49Na0.51)0.98Li0.02(Nb0.77Ta0.18-Sb0.05)O3-0.005BaZrO3ceramics were systematically studied. Research results showed that the BCBM frit can reduce the sintering temperature and have a remarkable effect on the density of ceramics, which indicated that the addition of BCBM acts as sintering aids. BCBM enhanced the Qm significantly and reduced the tanδ. The pure single phase ceramics can be obtained when doping1wt%BCBM and prepared by calcinating the powder at800℃and then sintered at1050℃, the uniform grain size and compact structure, displayed the best overall performance as follows:the d33=345pC/N, kp=44.5%, Qm=135, εT33/ε0=1208, tanδ=0.018. |
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