Preperation Of Temperature-Stable Dielctric Ceramics Based On Barium Titanate

The preparation and the dielectric property of temperature-stable dielectric materials based on Barium Titanate have been investigated in this dissertation.1. The BaTiO₃ nano-sized powders with particles about 60⁷0nm and fine-grained ceramics (0.7¹.0 μm) are prepared by Sol-Gel method. When the Nb/Co ratio is 1.5-2.0, the contents of Co and Nd both are 0.70 mol%, the X7R ceramics with dielectric constant around 3000 at room temperature were prepared at wide ranges of the calcining and sintering temperature.2. The nano-sized and homogeneous powders with particles about 40⁶0 nm and ceramics of Manganese-doped BaTiO₃ were prepared by Sol-Gel process. Because of the effect of the superfluous Manganese additives, the second phase such as hexagonal BaTiO₃ and BaMnO₃ are formed easily. The optimum calcining and sintering temperature are 800℃ and 1250℃ for 2 hours respectively. With the increase of Manganese content, the e-T curve gets flat although the dielectric constant of the ceramic decreases observably. As the Manganese content is within 0.50 mol%, the ceramic has not too much loss of dielectric constant, and other good characteristics such as dielectric loss and temperature dependence of permittivity accompanied it.3. The nano-sized and homogeneous powders with particles about 50nm and ceramics of Silicon-doped BaTiO₃ were prepared by Sol-gel process. Because of the effect of the superfluous Silicon additives, the second phase Ba₂TiSi₂O₈ is formed easily. The existence of Ba₂TiSi₂O₈ decreases the densification and the dielectric constant because it is not Ferro-dielectric. The optimum calcining and sintering temperature are 900℃ and 1250℃ for 2 hours respectively. With the increase of Silicon content, while the e-T curve gets flat, the dielectric constant increases firstlyand then decreases. When the Silicon content is 0.30 mol%, the dielectric constant (4081) is the highest.4. The nano-sized Nb-Co-Nd doped BaTiO3 and the Nb-Co-Nd-Mn-Si doped BaTiC>3 powders with particles about 50 and 60 nm respectively are prepared by Sol-Gel method. The Nb-Co-Nd doped BaTiC>3 powders which composed of tetragonal BaTiC<3 must be calcined at 128CC or ever higher. When the content of Nd is higher than 1.0 mol%, the temperature-stable are enhanced. When the Nb/Co ratio is 2.0, two peaks appear in the e-T curve. The dielectric constant of Nb-Co-Nd doped BaTiC?3 ceramic prepared by Sol-Gel method is higher than the one of ceramics prepared by solid-doping method. By addition of Mn and Si, the sintering temperature can be decreased and the e-T curve gets flat.