Study On The Structure And Piezoelectric And Dielectric Properties Of Na_0.5Bi_0.5TiO₃-K_0.5Bi_0.5TiO₃ System Ceramics Prepared By Sol-gel Method

In this dissertation, a sol-gel method was employed to prepare the (1-x)Na_0.5Bi_0.5TiO_3-xK_0.5Bi_0.5TiO₃((1-x)NBT-xKBT) (x=0～0.50 ) system lead-free piezoelectric ceramics. The synthesis and preparation, structure characteristics and piezoelectric properties of the material were investigated. The relation among the piezoelectric properties, the composition and the structure were also studied. The dielectric relaxation feature and phase transition of (1-x)NBT-xKBT ceramics and the influence of ferroelectric feature on the peizoelectric properties have been established in terms of experimental results.(1-x)NBT-xKBT powders have been synthesized by a sol-gel method. It was found that the mole ratio of water and alkoxide, pH of precursor solution and temperature of sols contrubuted greatly to the formation of homogeneous, transparent sol and gel, while the sintering temperature has a determinant role on crystalline structure and morphology of the sintered powders. The preferred synthesis conditions to prepare powders with a pure perovskite-type structure were ascertained and (1-x)NBT-xKBT powders were produced.XRD results reveal that (1-x)NBT-xKBT powders prepared by a sol-gel method were synthesized with a pure perovskite-type structure at the temperature of 650℃. And it was also found when x varies from 0.18 to 0.30, the ceramics have rhombohedral and tetragonal co-existed crystalline structure which is the morphotropic phase boundary (MPB). When x equals to 0.30, the piezoelectric constant d33 reaches maximum 150 pC/N, and when x equals to 0.26, electromechanical coupling factor K_q, and dielectric constantεT₃₃/ε₀ reach maximum they are 36.7% and 1107, respectively. Compared with the conventional solid-state reaction method, the ceramic specimens prepared by the sol-gel method exhibit more superior piezoelectric properties. At the same time, it was analysized that dielectric constantε_r and dielectric loss tanδas a function of temperature from room to 500℃under 1kHz,10kHz,100kHz frequency conditions, respectively, it was found that the system ceramics are relaxational ferroelectric material.