| Summary: | 碩士 === 國立東華大學 === 材料科學與工程研究所 === 87 === Barium titanate (BaTiO3), a popular electronic ceramic, has been mostly produced by the conventional solid state reaction in industry. The problem of compositional inhomogeneity is serious as the multilevel-doped BaTiO3 is considered. In this experiment, four kinds of multilevel -doped BaTiO3 were studied and prepared by a polymeric route. These systems included [(Ba1-zPbz)1-xLax](Ti1-yZry)1-x/4O3、[(Ba1-zSrz)1-xLax]Ti1-x/4O3、(LaxYyWw)-BaTiO3、and [(Ba1-zCaz)1-xLax] (Ti1-yZry)1-x/4O3. The Y and W label in the third type represented un-published symbols of the periodic table. Before the evaluation of dielectric properties, these systems were under the treatments of sintering, reduction- re-oxidation, sintering-oxidation, and sintering in different powder compacts.
The experimental results showed a good property for the third type of BaTiO3. At a specific composition with W in the 0.1 molar fraction, this BaTiO3 had a diffuse transition, a high dielectric permeability of 36,000, and a loss tangent of 0.26 at Curie temperature of 41C. It possessed a high permeability of 34,000 and a loss tangent of 0.19 at room temperature. At a specific composition with W in the 0.2 molar fraction, this BaTiO3 had a diffuse transition, a high permeability of 120,000, and a loss tangent of 0.38 at Curie temperature of ~-10C. It possessed a high permeability of 65,000 and a loss tangent of 0.54 at room temperature, while a permeability of >20,000 at the temperature less than 75C.
In this experiment, the effect of multilevel-doping on the dielectric properties of BaTiO3 has demonstrated in a complex way. A simple rule to predict the dielectric properties could not be obtained, especially when three dopants were added together. Nevertheless, a high dielectric material has been developed with a great potential in the future.
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