| With the development of electronic technology and industry, piezoelectric materials have been widely used in integrated circuits, automatic control, precision control, high-tech communications technology and so on. Sodium bismuth titanate (Na0.5Bi0.5TiO3, NBT) is a kind of perovskite-type relaxor ferroelectrics. NBT has been considered to be the most promising lead-free piezoelectric ceramics.In this thesis, (1-x) Na0.5Bi0.5TiO3-xBaTiO3 lead-free piezoelectric ceramics samples were prepared by traditional electronic techniques. Phase structure, dielectric and piezoelectric properties as a function of the presintering temperature have been investigated. Furthermore, effect of La2O3 addition on microstructure and electrical properties of (Na0.5Bi0.5)0.94Ba0.06TiO3 ceramics samples with a composition in morphotropic phase boundary (MPB) have been investigated. Piezoelectric properties of the ceramics samples has been suggested based on experimental.Reasonable parameters is prerequisite to maintain dense ceramics with excellent properties. From the powder of pre-synthesis temperature, the influence of parameters on the phase composition and dielectric properties of (1-x)Na0.5Bi0.5TiO3-xBaTiO3 powder was investigated. The presintering temperature of (1-x)Na0.5Bi0.5TiO3-xBaTiO3 powder have a major impact on the crystalline phase of ceramics. The single perovskite structure is difficult formed with the lower temperature, the density of ceramics was reduced with the higher temperature. The main results and the conclusions are as follows:when x is less than 0.06, the reasonable presintering temperature should be 850℃; when x is equal to 0.06, the presintering temperature should be 900℃; when x is greater than 0.06, the presintering temperature should be above 950℃.0.94Na0.5Bi0.5TiO3-0.06BaTiO3 ceramics samples have good dielectric properties with the flat curve between temperature dependence and dielectric constants. In addition, the dielectric loss of 0.94Nao.5Bi0.5Ti03-0.06BaTiO3 ceramics samples was the lowest in the measured samples. With presintering temperature increased, the dielectric properties of (1-x)Na0.5Bi0.5TiO3-xBaTiO3 ceramics samples was improved.Phase structure and electric properties of (Na0.5Bi0.5)0.94Ba0.06TiO3 ceramics samples as a function of amount of dopant La2O3 were discussed. Microstructure and morphology characterization was characterize by means of XRD, SEM and other analysis tools; electrical properties of ceramics samples were measured and analyzed by means of quasi-static meter. The main results and the conclusions are as follows:①The XRD results revealed that all samples showed single perovskite structure, La3+ can completely enter solid solution lattice, and the ceramics samples still have three-four co-existence of the crystal structure. The SEM results showed that doping a small amount of La2O3 can improve microstructure of (Na0.5Bi0.5)0.94Ba0.06TiO3 ceramics;②With the increase of doping, the frequency dispersion and diffuse phase transition were remarkable near the ferroelectric-antiferroelectric dielectric peak. Disorder increasing by entry of La3+ makes the relaxation of the system enhance.③With the increase of La2O3 addition, the increase in the number of A vacancies weaken coupling between the cation of A bit and BO6 octahedron. The long-range coulomb was destroyed an the stability of ferroelectric domain reduced. The dielectric peak of ferroelectric-antiferrolectric moved to low temperature side. Finally, the characteristic of relaxor ferroelectric showed at room temperature.④Adding a amount of La2O3, the dielectric constant increases with the doping, showing a "soft doping" feature. Adding higher amounts of La2O3, the dielectric constant decreases rapidly. The increase of La2O3 doping raised the disorder of A bit, at room temperature antiferroelectric phase has emerged. Antiferroelectric region makes the spontaneous polarization declined. Thus, it leads to the decline in dielectric constant and piezoelectric constant. |
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