Preparation Of Tetragonal Barium Titanate Nanotubes And Size Effects Investigation Of Barium Titanate Nanocrystalline

The contents of this thesis are preparation of tetragonal Barium titanate(BaTiO3nanotube arrays, using the titania nanotube arrays (TiNTs) as the template fabricated by the anodic oxidation method. The Tetragonal BaTiO3nanotube arrays were synthesized by hydrothermal method combined with an annealing process. We also investigated the size effect on phase transitions and dielectric behaviors of nano-crystalline BaTiO3ceramics, the conclusion we obtained can be useful for synthesizing one-dimensional ferroelectric materials.A variety of TiNTs were prepared in electrolytes containing certain degree of F" ion, we choose the best formula after modifying the parameters of anodic oxidation. The length of as-prepared TiNTs nanotube arrays can reach10μm, and the inner diameter locates at50～1OOnm. Afterwards, we using the TiNTs as templates, taking the hydrothermal as the method, the hydrothermal temperature, the concentration of the hydrothermal solution and the hydrothermal time into consideration, Tetragonal Barium titanate (BaTiO3) nanotube arrays were first successfully prepared, The in-situ chemical conversion of TiO2nanotube array templates ensured that BaTiO3maintained the morphology of the nanotube architectures. Moreover. X-ray diffraction and Raman spectrum characterization were used to confirm that the BaTiO3nanotube arrays had a tetragonal phase after the use of a simple annealing technique. Typical hysteresis loops showed their ferroelectricity, with the remanent polarization and coercive fields being2.57μC/cm2and2.52kV/cm, respectively. The relative dielectric constant of the tetragonal BaTiO3nanotube arrays reached up to1000and the dielectric loss was as low as0.02at1kHz at room temperature.Size effect on the domain, phase transition, dielectric properties of BaTiO3are studied, Multiple ferroelectric domains present in nano-crystalline BaTiO3ceramics observed by transmission electron microscope (TEM). Tetragonal (T) and orthorhombic (O) at room temperature and orthorhombic coexists with rhombohedral (R) at low temperature mixture structures are proved by in-situ temperature high resolution x-ray diffraction (HRXRD). The distortion of phase transitions from cubic (C) to T to O and further to R support the existence of an intrinsic mechanism, and the phase transitions of O-R and T-0are more susceptible to GS than C-T. The decrease tendency of relative dielectric constant for nano-crystalline BaTiO3ceramics ascribes grain boundary effects and residual internal stress. Dielectric loss for fine grain size (FGS) BaTiO3is lower than coarse grain size (CGS) before Curie phase transition due to diffuse phase transition and grain boundary effects.Size effect on the crystalline phase contents has been investigated for BaTiO3ceramics varied from100to8nm by means of X-ray diffraction and Raman spectroscopy techniques. Mixed phases of tetragonal and orthorhombic at room temperature were corroborated by Raman spectroscopy. Rietveld refinement for X-ray diffraction data revealed that a locally orthorhombic structure preceded the globally tetragonal form with the grain decreasing, and a modified brick-wall model was used to predict the dielectric constant between100and8nm, which demonstrated that grain boundary effects, internal stress and Pinning effect took the dominant role in determining the ultrafine nanocrystalline BaTiO3ceramics dielectric constant.