Piezoelectric Property And Dielectric Tunability Of Patassium Sodium Niobate Based Materials

The piezoelectric materials are those with piezoelectric effect. The pressure sensors,acceleration sensors, piezoelectric loudspeakers, ultrasonic motors, and micro displacement controllers can be designed by using the piezoelectric effect. Nowdays, the piezoelectric materials have been widely used in many areas. While, the piezoelectric materials usually show ferroelectric property, pyroelectricity, dielectric tunability, and electro-optical property and have been one of the most widely used functional materials. During the past decades, the lead-based piezoelectric materials have always been dominating the piezoelectric application area due to their excellent piezoelectric property and the good temperature stability. However, the lead of these materials is poisonous and harmful to the environment and human. Many countries have carried many policies to limit the use of lead-based piezoelectric materials to minimize the harmfulness of lead. So, it is emergent to find lead-free piezoelectric materials to replace the application of lead-based materials, which has been one of important subjects of materials research. By far, KNN-based piezoelectric materials have been considered to be one of most promising candidates for lead-based materials due to his excellent piezoelectric, ferroelectric, and dielectric properties. They may also be used in high-temperature areas due to their high Curie temperature(420 ℃). However, many factors, like low density, the piezoelectric property, and the bad temperature stability of the high-performance materials still inhibit the application of KNN-based materials. Thus, it is significant to study the assistant sintering, the improvement of the piezoelectricity, and the way to optimize of the temperature stability of KNN-based materials. In addition, it can expand its application area to study the dielectric tunability of KNN-based materials.The mechanism of the defect and the internal field induced by the volatilization of the A-site elements was analyzed at first. The domain pinning effect of the defect and the internal field, as well as their native effect on the piezoelectricity, are analyzed. Then, it was proposed that the piezoelectric and ferroelectric properties can be enhanced by compensating the volatilization of the A-site elements and lowering the concentration of the defect and the domain pinning effect. Then, the KNTN-Na F ceramics were prepared using the solid state method at each temperature for different doping ratios. The structure of the samples was determined by XRD and the microstructure was determined by SEM. The effect of Na F on the the sintering temperature, the density, and the grain size was studied. The ratio of A/B site elements was determined by the X-ray fluorescence and then, the compensation effect of Na from Na F for the A-site elements was analyzed.The doping mechanism, including donor and acceptor, of different abnormal-valance ions was analyzed at first. The effect of them on the piezoelectric, ferroelectric, and dielectric properties was also analyzed. Then, the Yb3+ was introduced to enhance the piezoelectric properties of KNN ceramics. The Yb-doped KNN samples was prepared at it own temperature with various doping ratios. The occupation of Yb3+ in the KNN crystal lattice was determined by XRD. The effect of Yb doping on the density and the grain size was studied by SEM. At last, the piezoelectric, ferroelectric, and the dielectric properties were studied. The effect of the Yb occupation on the porperties was also analyzed.The temperature dependence of the KNN-based materials with room-temperature phase transition was analyzed. Then, it was proposed that the KNN-based materials with tetragonal phase should show both high piezoelectric property and excellent temperature stability. The(K0.45Na0.55)0.94Li0.06TaxNb1-xO3 ceramics with tetragonal phase was designed and the samples were prepared by the solid state method. The structure was determined by XRD. The dielectric constant of the orthorhombic and the tetragonal phase was studied by the temperature dependence of the dielectric property. At last, the piezoelectric property and the temperature dependence of these samples in the temperature range 20-80 ℃ were studied. La was introduced to eliminate the effect of the phase transition on the temperature stability to further improve the temperature stability of these ceramics.The mechanism of the dielectric polarizations and their response under external field of dielectrics was analyzed. It was proposed that the materials should show excellent dielectric tunability in the vicinity of the Curie temperature due to the presence of the nano-clusters. The KTa0.6Nb0.4O3 crystal was designed and the the Curie temperature was determined by the temperature dependence of the dielectric property. Then, the dielectric tunability of KTa0.6Nb0.4O3 crystal was studied and the contribution of the nano-clusters to dielectric property was analyzed in terms with the Landau-Ginzburg-Devonshire thermodynamic theory completed with the Langevin term. The Fe-doped KNTN ceramics were prepared by the solid state method. The structure and the occupation of Fe3+ in the crystal lattice were studied by XRD. Then, the ferroelectric and the ferromagnetic properties were studied. At last, the dielectric tunability by the external magnetic field was studied.