| The main interest of this thesis lies in the crystal structure, ferroelectric and dielectric properties of typical BLSFs Bi3TiNbO9 (BTN) and its intergrowth ceramics Bi3TiNbO9– Bi4Ti3O12 (BTN-BIT).Bi3NbTiO9 was discovered by Aurivillius in 1949. Subbarao and Newnham showed it to be a ferroelectric with the highest known Curie point in the BLSF family at that time of 940oC. However, the information about its electrical properties and the effect of doping is still very limited. In the present, most studied of the Bi3NbTiO9 compounds have been as a function of the structure and improvements of the sample's preparation. Ceramic pellets of Bi3-xNdxTiNbO9 (NBTN-x, x = 0.00, 0.25, 0.50, 0.75) were prepared by the conventional solid-state reaction method with starting metal oxides Bi2O3 (99.0% purity), TiO2 (98.0% purity), Nd2O3 (99.0% purity) and Nb2O5 (99. 5% purity) powder. In this work, we have measured the dielectric properties in the vicinity of the transition temperature of NBTN-x for the first time, and we have also studied the crystal structure, microstructure, ferroelectric and dielectric properties of pure bulk BTN-x ceramics.The microstructure of NBTN-x, x = (0.00 ~ 0.75) ceramics were studied by X-ray diffraction and Raman spectroscopy. With different Nd3+ contents (x), NBTN-x ceramics bring out orthorhombic phase (x = 0) while the end number (x = 0.75) is determined to exhibit tetragonal phase by X-ray diffraction. Raman spectra were also used to explain this inflect of microstructure, which resulted from the fact that Nd3+ substitutes for the Bi3+ in A site rather than in the [Bi2O2]2+ layer, the tilt of the Ti/NbO6 octahedra decreased with increasing x. The hysteresis properties of the BTN-x showed low polarization values (2Pr = 3.7μC·cm?2). Nd3+ doping BTN showed no improvement on ferroelectricity. With different Nd3+ contents (x), The curie temperature declined rapidly from 940oC (x = 0) to 480oC (x = 0.75). The decreasing curie temperature of BTN-x implicated the disorder of lattice constant; correspond with the results of X-ray diffraction and Raman spectroscopy. The activation energies fitted from cole-cole plots were 0.648eV, 0.757eV, 0.999eV and 1.003 eV, respectively.Intergrowth ceramics Bi3TiNbO9– Bi4Ti3O12 (BTN-BIT) were prepared. The X-ray diffraction (XRD) and Raman patterns show that the intergrowth structure has been formed and no second phases exist. This results in a large increase of remnant polarization from 3.74 to 10.17μC/cm2 but the hysteresis loop appears no saturated. We have tried several methods including the changes in experimental approach, cool rapidly by placing it in H2O2, sintering in oxygen atmosphere to improve its ferroelectric property. But no perfect effect has been received.SrBi2-xLnxNb2O9 (Ln=La, Nd and Sm) indicates that Bi3+ ions in the Bi2O2 layers could be replaced by Ln ions. The transition from a normal ferroelectrics to a relaxor-type ferroelectrics was induced by doping of Ln ions into Bi2O2 layers. The substitution of Ln ions for Bi3+ ions resulted in a decrease in the coercive field and the remanent polarization. The finding of the relaxor behavior in SrBi2-xLnxNb2O9 would make for the better understanding of the relaxation nature of layered perovskites. |
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