Preparation And Characterization Of Nanoparticles Doped BaTiO₃-based Ceramics

Barium Titanate (BaTiO₃) is widely used in preparation of capacitance, thermal resistor, energy conversion device, for their exceptional ferroelectric, piezoelectric, pyroelectric and dielectric properties. Especially, it is mostly applied in making multilayer ceramic capacitor (MLCC) materials. At present, MLCC has a trend of high credibility, specific votume (small size and large capacity) and low cost. So, researchers have paid their attention to the preparation of high pure BaTiO₃ nanopowders, and doped BaTiO₃. In this paper, Monodisperse TiO₂, ZrO₂ and Cu nanoparticles were prepared through two-phase method using oleic acid (OA) as surfactant. Monodisperse BaTiO₃ powders and ceramics were synthesized with H₂TiO₃ through co-precipitation method also using OA as surfactant. Nd(OH)₃ nanowires and square-shaped nanostructures of Co₃O₄ synthesized via hydrothermal method. Nb₂O₅ nanoparticles were prepared by precipitation method. And nanosized Nd(OH)₃, Co₃O₄ and Nb₂O₅ doped BaTiO₃-based ceramics with high dielectric constant and low sintering temperature were prepared, respectively. Furthermore, nanosized Nd(OH)₃, Co₃O₄ and Nb₂O₅ complexly doped temperature-stable BaTiO₃-based ceramics with high dielectric constant were prepared.1. Monodisperse TiO₂ nanorods, ZrO₂ and Cu nanoparticles were synthesized through two-phase method using OA as surfactant and hexamethylene as solvent. The concentration of NaOH, reaction time or the ammonia replacing NaOH has slight effect on the morphology of TiO₂ nanorods. But the TiO₂ longer nanorods were obtained with ethanol as solvent and the Ca(NO₃)₂ in solution.2. The content of OA has slight effect on the size of tetragonal ZrO₂ nanoparticles. But the diameter of ZrO₂ nanoparticles increased withont the surfactant of OA, and the ZrO₂ nanoparticles were composed of pure monoclinic and tetragonal phase. Nd(OH)₃ nanowires and cubic nanostructures of Co₃O₄ were synthesized by hydrothermal method. Nb₂O₅ nanoparticles were prepared by precipitation method. The concentration of precursor N₂O₅, or the rate of drop ammonia has effect on the size and morphology of Nb₂O₅ nanoparticles. Two-phase method has a potentiality in controlling the size and microstruction of nanoparticles, and can be used to prepare other nanomaterials. At the same time, this method establishes a base in preparing nano-dopants for BaTiO₃.3. BaTiO₃ powders were synthesized with H₂TiO₃ through co-precipitation method using OA as surfactant, and the powders were all in nanometer scale which size were rang from 30 to 50 nm. The powders were calcined at 850℃for 2 h and obtained pure BaTiO₃ phase powders except for [H₂TiO₃]/[OA] 1:1. After sintering, the ceramics were completely consisted of tetrahedron BaTiO₃ phase. The density of the ceramics([H₂TiO₃]/[OA] rate of 2:1.), which were sintered at 1250℃for 2 h , was 5.6 g·cm-3, room temperature permittivity reached to 2586, while the dielectric loss was 0.020.4. The Nd-doped BaTiO₃ nano-powders were synthesized by the reactive templated grain growth method using the Nd(OH)₃ nanowires as template. The main phase was BaTiO₃ and the impure phases were TiO₂ and Ba₆Ti₁₇O₄₀. The morphology of BaTiO₃ nano-powders was nanorod and the length shortened as the calined temperature increased.5. A nano-doping process was introduced in preparing Nd(OH)₃ nanowires doped BaTiO₃-based dielectrics. The dielectric constant first increased and then decreased with the content of Nd(OH)₃ (0.5～2.5 mol%) increased and the courier peak moved towards low temperature. When the content of Nd(OH)₃ was 1.0 mol%, the dielectric constant also first increased and then decreased as the calcined temperature and sintering temperature increased. The density of ceramics calcined at 900℃for 2 h and sintered at 1250℃for 2 h was 5.8 g·cm-3, room temperature permittivity was 3873, and the dielectric loss was 0.016.6. While the dielectric constant decreased as the content of Co₃O₄(0.5～2.5 mol%) increased and the courier peak didn't change. When the content of Co₃O₄ was 1.5 mol%, the dielectric constant also decreased as the calcined and sintering temperature increased. The density of ceramics calcined at 800℃for 2 h and sintered at 1250℃for 2 h was much compact with high dielectrics constant at courier point, which was 10995. Nano-doping process can improve the dielectrics constant, reduce the sintering temperature, and obtain grain refining ceramics.7. The BaTiO₃-based dielectrics with low sintering temperature, high dielectrics constant and well temperature-stable were prepared by nano-doping with different size and morphology of Nb₂O₅ nanoparticles. Especially, using the monodispersed Nb₂O₅ nanoparticles as nano-dopant can obtain the "core-shell" structure. Nanosized Nd(OH)₃, Co₃O₄ and Nb₂O₅ complexly doped temperature-stable BaTiO₃-based dielectrics were prepared by solid-state method. The nano-doping ceramics sintered at 1250℃for 2 h with fine grain size, high density, and satisfy with the requirement EIAX7R.