Study On Preparation And Modification Properties Of Potassium-sodium Niobate-based Lead-free Piezoelectirc Ceramics

In this dissertation, three setups of lead-free piezoceramics asK_0.49Na_0.51NbO₃-xBaTiO₃-0.06BaZrO₃、(K_0.49Na_0.49)NbO₃–BiFeO₃–0.05LiTaO₃�'�K_0.49Na_0.51NbO₃-BaTiO₃-BaZrO₃-LiNbO₃were prepared by conventional solidstate reaction method. The different elements influence on the microstructures,phase transitions, dielectric and piezoelectric properties in KxNa1-xNbO₃thethree systems of lead-free piezoelectric ceramics were investigated.First of all, the lead-free piezoelectric ceramics （0.94-x）K_0.49Na_0.51NbO₃-xBaTiO₃-0.06BaZrO₃（abbreviated as KNN-BT-BZ） with x=0⁰.04were researched in this study. The results indicated that all samples havea single perovskite structure. With the increasing of BaTiO₃content, thepiezoelectric constant d₃₃and the planar electromechanical coupling factor k_pincrease first and then decrease, the mechanical quality factor Q_mand dielectricconstant ε^T₃₃/ε₀increase, the dielectric loss tanδ reduce. When x=0.03, theceramic exhibited excellent electrical performances as follows: d₃₃=322pC/N，k_p=42%，Q_m=193，ε^T₃₃/ε₀=423and tanδ=0.045.The results of the lead-free piezoelectric ceramics （0.95-y）(K_0.49Na_0.51)NbO₃–yBiFeO₃-0.05LiTaO₃（y=0⁰.10, abbreviated as KNN-BF-LT） showed that a morphotropic phase boundary between orthorhombic andtetragonal ferroelectric phases has been identified in the composition range of0.04≤y≤0.06.With the increasing of BiFeO₃content, the piezoelectric constantd₃₃and the planar electromechanical coupling factor k_pincrease first and thendecrease, and dielectric constant ε^T₃₃/ε₀increase, the dielectric loss tanδ increasefirst and then decrease. When y=0.04, the ceramic exhibited excellentelectrical performances as follows: d₃₃=180pC/N， kP=38.2%、 ε^T₃₃/ε₀=372、tanδ=0.027。Finally,the LiNbO₃doping effected on the microstructures, phasetransitions, dielectric and piezoelectric properties in （1-z）[0.91K_0.49Na_0.51NbO₃-0.03BaTiO₃-0.06BaZrO₃]-zLiNbO₃（KNN-BT-BZ-LN） wasstudied in the compositional range of z=0.00⁰.08. The experimental studiesshowed that a morphotropic phase boundary between orthorhombic andtetragonal ferroelectric phases has been identified in the composition range of0.05<z<0.07.The piezoelectric constant d₃₃and the planar electromechanicalcoupling factor k_pincrease first and then reduced with the increasing ofLiNbO₃doping, but the mechanical quality factor Q_mappeared at the opposite tendency.At the same time, dielectric constant ε^T₃₃/ε₀and dielectric loss tanδ keepincreasing, when z=0.06, the ceramics samples have optimal properties:d₃₃=316pC/N， kP=40.3%， tanδ=0.069， ε^T₃₃/ε₀=1547， Q_m=56。...