KNN-based Lead-free Piezoelectric Ceramics With High Electric Breakdown Strength, Piezoelectric Properties And Dielectric Properties

With both environmentally friendly and excellent electrical characteristics, KNN has been the hotspot in research of lead-free piezoelectric ceramics. But the research on KNN-based piezoelectric ceramics mostly focuses on the performance improvement, and few reports of its practical application are mentioned. With the discovery of the characteristics of the KNN-based piezoelectric ceramics with high breakdown field strength, the purpose of this paper is to prepare a variety of ceramic material with high dielectric constant, high breakdown field strength and good piezoelectric properties, satisfying the various performances as a practical application of ceramic capacitor. At the same time, it is expected to replace lead-based piezoelectric material in some piezoelectric and ferroelectric areasFirstly, a basic formula of the ceramic material with high dielectric constant is selected. By optimizing the preparation method and process, the traditional solid phase method is considered to be more useful to material performance. The main performance parameters for ceramics at room temperature are:d33=220pC/N, kp=33.6%,εT33/ε0=2089, tanδ=0.0562, Eb=10kV/mm.By Ni2O3doping,(K0.435Na0.53Li0.035)(Nb0.872Sb0.09Ta0.09) O3+x mol%Ni2O3(x=0,0.025,0.05,0.1) series of ceramic materials was prepared. Comprehensive performance of the ceramics is the best when Ni2O3doping amount is0.025mol%, the specific performance parameters are:d33=244pC/N, kp=34.1%, εT33/ε0=2000, tanδ=0.0377, Eb=16.3kV/mm.The results show that the addition of Ni2O3plays a positive role on the performance of the ceramics, especially on the piezoelectric properties and the breakdown field strength.Four different metal oxides Fe2O3, La2O3, Y2O3and Nd2O3are used for contrast experiment, the doping amount of all the metal oxides are0.05mol%. Results show that the properties of rare earth metal oxide doped ceramics hardly increase, to some degree, all the properties of the ceramics decrease. However, the properties of Fe2O3doped ceramics are improved significantly. On this basis, a series of experiments by doping Fe2O3are conducted. The experimental formula is in accordance with (K0.435Na0.53Li0.035)(Nb0.82Sb0.09Ta0.09)O3+x mol%Fe2O3(0≤x≤0.5). When x=0.2, the best performance of d33=350pC/N, kp=44.9%, ε33T/ε0=2532, tanδ=0.0331, and Eb=16.3kV/mm are achieved. According to data above, the properties of Fe2O3doped ceramics are greatly increased. In particular, the breakdown field strength is comparable to the Ni2O3doped ceramics, and the pretty high dielectric and piezoelectric properties of KNN-based piezoelectric ceramics are obtained, which is among the advanced level of current research in this field.Through the preparation methods and process optimization, the ceramic material formula with high dielectric constant is obtained. By doping different metal oxides, KNN-based lead-free piezoelectric ceramic materials with high dielectric properties, high breakdown field strength as well as high piezoelectric properties are obtained, which make it practical in high voltage ceramic capacitors and more promising to replace PZT based ceramics.