Bismuth Titanate Materials: Synthesis, Characterization And Their Properties

The synthesis, characterization, optic and photocatalytic properties of Bi₁₂TiO₂₀, Bi₂Ti₂O₇ and Bi₄Ti₃O₁₂ nanoparticles and the effects of composition and crystal lattice upon microstructural, dielectric, piezoelectric and electrical properties of pure and doped Bi₄Ti₃O₁₂ ceramics have been widely investigated. The key points of this dissertation are described as follows.The Bi₁₂TiO₂₀ nanowires have been synthesized via a simple solution-phase hydrothermal process, then complex architectures, such as microspheres, mircoflowers, nanrods and nanowires, were prepared through the same route. The effect of reaction parameters, such as temperature, pH and PVA concentration, and reaction time, were studied in order to control the morphologies. A possible growth mechanism is proposed to explain the transformation of nanoparticles-mircoflowers- nanowires-microspheres. Most importantly, the optic and photocatalytic properties of these samples are further investigated, displaying high photocatalytic activities of nannowires. Besides, the Bi₂Ti₂O₇ and Bi₄Ti₃O₁₂ spherical colloids have been synthesized by the hydrothermal process without any surfactant or template, also the the photocatalytic properties of Bi₂Ti₂O₇ and Bi₄Ti₃O₁₂ well-defined spherical architectures were investigated. In addition, the Bi₄Ti₃O₁₂ nanoparticles have been fabricated via metal-organic polymeric precursor, and their PL properties also were investigated. Then the well-dispersed Bi₄Ti₃O₁₂ nanocrystals were synthesized by PBR(Peroxide-Based-Route) assisted with inverse microemulsion process. Analysis of nonisothermal DSC data yielded the activation energy of crystallization (Ea) and the Avrami exponent (n), respectively.The effects of composition and crystal lattice upon microstructure, dielectric, piezoelectric and electrical properties of BIT, Bi4Ti3-xWxO12+x+0.2wt%Cr2O3(BTWC), Bi₄Ti_3-2xNb_xTa_xO₁₂(BTNT) and Bi₄Ti_3-2xNb_xTa_x-ySb_yO₁₂(BTNTS) ceramics have been widely investigated. The process of as-synthesized BIT were optimized and the main parameters were determined, as well as the piezoelectric coefficient (d₃₃) of BIT is 8pC/N. As for BTWC, the results shown the lattice parameters; the second phase existed during the higher level of W/Cr doping; the dielectric constant and loss increased at room temperature with increase of doping content; the higher value of d₃₃, 22pC/N, was obtained for the sample with x=0.025, which may result from the lower conductivity. With regard to BTNT and BTNTS, the results shown the orthorhombic structure for all samples; the addition of Nb/Ta caused a remarkably suppressed grain growth while there is no much difference upon grain size for BTNTS; as the doping content increased, the Curie temperatures of BTNT decreased significantly, even to 630oC while it's no big difference for BTNTS. The co-doping at B-site could induce the distortion of oxygen octahedral and reduce the oxygen vacancy concentration, resulting in the enhancement of d33. Especially, the highest values of 26 and 35pC/N, were obtained for Bi₄Ti₂.98Nb₀.01Ta₀.01O₁2 and Bi₄Ti_2.98Nb_0.01Ta_0.002Sb_0.008O₁₂, respectively. The activation energy associated with the electrical relaxation and DC conductivity were determined from the electric modulus spectra, suggesting the movements of oxygen ions are possible for both ionic conductivity as well as the relaxation process. To ascertain the electrical conduction mechanism in the ceramics, various physical models have been proposed, suggesting the conductivity behavior of the ceramics can be explained using correlated barrier hopping model.