Study On Structure And Properties Of （K, Na, Li, Bi）（Nb, Ti）O₃Piezoelectric Ceramics

In this dissertation, KNN-based lead-free piezoelectric ceramics were synthesizedby solid-state reaction method. The phase structure, microstructure, dielectric andpiezoelectric properties of ceramic samples were investigated in detail. The mainresearch content is comprised of three parts as follow:（1）（1-x）K0.5Na0.5NbO₃-x（Na0.8K0.2）0.5Bi0.5TiO₃（x=0-5%） lead-free piezoelectricceramics. The effects of the content of （Na0.8K0.2）0.5Bi0.5TiO₃on the phase,microstructure, dielectric and piezoelectric properties of samples were investigatedcarefully. The results show that all samples possess pure perovskite structure. With theincreasing amount of （Na0.8K0.2）0.5Bi0.5TiO₃, the phase structure of samples at roomtemperature changes from orthorhombic symmetry to tetragonal symmetry and both thepiezoelectric constant d33and planar coupling factor kpof samples increase firstly thendecrease while Curie temperature decrease gradually. A polymorphic phasetransition（PPT） from orthorhombic to tetragonal symmetry locates in the composition of2%≤x≤3%in this system and the ceramic sample with x=3%own peak piezoelectricproperties （d33=189pC/N, kp=41%Qm=96, tanδ=0.028）. In addition, diffusion coefficientof samples increase gradually and relaxation properties enhanced with the increase of xvalue.（2）[（NaxK（1-x））0.985Bi0.015](Nb0.97Ti_0.03)O₃（x=0.40-0.65） lead-free piezoelectricceramics. The influences of different x on the phase structure, microstructure,piezoelectric and dielectric properties of samples were studied in detail. The resultsindicate that all samples possess perovskite structure. With the increase of x content, thegrain size of samples increase firstly then decrease; the Curie temperature of all samplesare in the range of340℃～365℃and mechanical quality factor Qmvalue is about80.The polymorphic phase transition （PPT） from orthorhombic to tetragonal symmetrylocates in the composition of0.45≤x≤0.63in which the ceramic samples possess highpiezoelectric properties. The ceramic sample in the composition of x=0.60own toppiezoelectric properties （d33=253pC/N，kp=0.43，tanδ=0.024，Qm=73，TC=359℃） in thissystem.（3）（1-x）(K_0.48Na_0.48Li0.04)NbO₃—x（Na0.8K0.2）0.5Bi0.5TiO₃（x=0-3%） lead-freepiezoelectric ceramics. The influences of different x on the phase structure,microstructure, piezoelectric and dielectric properties of samples were investigated. Theresults show that Orthorhombic-Tetragonal phase transition temperature and Curietemperature decrease gradually with the increase of x content while both the piezoelectricconstant d33and planar coupling factor kpof samples increase firstly then decrease. The typical PPT locates in the composition of0.5%＜x＜1.5and the ceramic with x=1%possess both good piezoelectric properties （d33=226pC/N，kp=0.41） and high Curietemperature（437℃）. However, the piezoelectric properties of the ceramic near PPT issensitive to temperature.