The Preparation And Mechanism Studies Of Potassium Tantalate Niobate And The Related Composites

With the development of laser and infrared detection techniques, research in the field of pyroelectric materials and their application has expanded at a breathtaking pace. Many excellent pyroelectric devices, such as pyroelectric detector and thermal imaging system etc, have been manufactured, which can be used in industry, national defence and daily life. Composites of ferroelectric ceramic inclusions in a polymer matrix have been widely investigated, which combine the advantages of the polymer matrix with those of the ceramic phase. Potassium tantalate niobate (KTN) have extraordinary electro-optic, pyroelectric effects and is a very potential pyroelectric material.To solve the problems in the practical application of KTN materials caused by high preparation temperature, the objective of the current work is to explore new synthesis methods: hydrothermal, simplex solvothermal and mixed solvothermal synthesis; then we attempt to explore a composite based on KTN with outstanding pyroelectric property. Therefore the probable approachs to improve the pyroelectric property of 0-3 ferroelectric composites are phenomenologically discussed from the theoretical point of view. Moreover, we have discussed the polarization mechanism of the material and predict the pyroelectric and piezoelectric properties of 0-3 ferroelectric composites under different poling conditions.In view of the obstacle of the practical application of KTN material, novel preparation methods with the advantage of mild reaction condition are explored. We employ the hydrothermal processing route including hydrothermal, simplex solvothermal and mixed solvothermal method to prepare the KTN powders. Finally high-purity KTN powders have been successfully synthesized by systematic abundant experiments. The synthesis mechanism is discussed thoroughly. The present mixed solvothermal method provides a new potential route for synthesizing ferroelectric potassium tantalate niobate material. The KOH concentration and the solvent composition have important effects on the final products. XRD, SEM and TEM investigations exhibit that the typical samples solvothermally synthesized are nanosized, well-crystallized and single crystalline. The KTN particle shows the pseudo-cubic to tetragonal transition with increasing crystallite size. It is believed that supercritical isopropanol in the solvent plays an important role in synthesizing KTN nanoparticles under milder conditions than hydrothermal route.0-3 KTN/P(VDF-TrFE) bulk composites has been fabricated by hot-pressing method. Dielectric, ferroelectric and pyroelectric properties have been investigated primarily. XRD and SEM results indicate that the product is well crystallized without any other impurity phase, and KTN powders is dispersed uniformly in a P(VDF-TrFE) matrix. The dielectric constant of the composite decreases greatly relative to that of ceramic and is about 100 at room temperature. KTN/ P(VDF-TrFE) 0-3 composite thin films have been fabricated using the spin-coating method. It shows that the film is quite homogeneous and shows better interfacial integration than bulk composites.In order to explore the possible methods for improving the pyroelectric effect of 0-3 ferroelectric composites, a new comprehensive model has been developed for the pyroelectric activity of 0-3 ferroelectric composites which includes additional contributions from the electrical conductivity of the constituents and the frequency of measurement when the secondary pyroelectric effect resulting from the coupled thermoelectroelastic behavior is considered. The boundary conditions are obtained in terms of the Laplace equation and Maxwell's equations. The analytical expressions have been derived for primary and secondary pyroelectric coefficients. The effects of the electrical conductivity of the matrix and the measuring frequency on the pyroelectric property have been investigated in detail. Our model can reflect comprehensively the pyroelectric property of the material and shows reasonably good agreement with experimental data.To better understand the physical process behind poling of 0-3 composite, we have investigated the effect of electrical conductivity of the constituents on the poling behavior of the ceramic inclusions in 0-3 ferroelectric composites. A new model for the pyroelectric and piezoelectric properties in terms of the poling conditions (poling field and poling time) has been developed to include the electrical conductivity. Simulated results show that conductivity plays an important role in the poling process. Properly increasing conductivity of the matrixσm can enhance the polarization in the ceramic inclusion of the composite Pi , therefore make the poling of the composite more efficient. On the contrary, higher conductivity of the ceramic inclusionσiresults in lower polarization Pi , which is unfavorable to the poling of the composite. The model predicts the pyroelectric and piezoelectric properties under different poling conditions, which agrees well with the corresponding experimental data.