Low Temperature Synthesis And Dielectric Properties Of Nanometer-sized Batio₃-based Solid State Solution

Electronic ceramic material is an important field in material science, which is applied to semiconductor, piezoelectricity, dielectric material and insulation material. BaTiO₃ as a kind of very important dielectric material, has been widely applied in the production of electric components such as high-property ceramic capacitor, multilayer ceramic capacitor, PTC heat-sensitive resistance, resonance implement, medium amplifier, and is indispensable in electronic industry. Its dosage is largest as capacitor material and basic matrix of electric function ceramic at present.In order to meet the high-capacity need of dielectric material, preparing symmetrical and little-size nanometer powder is the sticking point. In my research work, firstly synthesis methods of pure BaTiO₃ were probed to obtain excellent crafts of powder preparation. Nanometer-sized BaTiO₃ powders were prepared with inorganic salt, such as TiCl₄, Ba(OH)₂, as raw material by low temperature solid state reaction. Powders synthesized by this method. XRD analysis showed that the powders were cubic provskite structure. The powders are less aggregation and symmetrically ball-like through TEM analysis. Through changing the conditions of reactive system, such as reactant concentration, hydrolysis time, grinding time, drying time, the best crafts parameters were obtained, which can prepared small-sized and evenly scattered nanometer BaTiO₃ powder. The powders synthesized by the method were sintered to ceramic, and measure their capability. The ceramic has good capacity. From the experiment, the relationship of capacity and grain size is determined.But because of the structure of BaTiO₃ molecule, it has some shortcoming. For example, it has the highest dielectric constant at 120℃(～10⁴), while its dielectric constant at room temperature is only 1/6 of the Curie point, which greatly limited its practical applications. Otherwise, its dielectric loss is large, and its capacity changes greatly with the variety of temperature. It is hypothesized theoretically that the Curie point of BaTiO₃ may be lowered and broadened when the large Ba²⁺ ions are partially replaced by small-sized ions, or inactive Ti⁴⁺ ions are partially replaced by active ions. Additionally, the difference between ceramic and single crystal is that there are many crystal boundary in the ceramic, which have important effects on the performance of material. Thus it is needed to adulterate some ions into the powder grain and crystal boundary. At present, solid phase adulteration was adopted in the production process of electric component in industry. The oxides of Sr, Zr and some rare earth elements are adulterated in BaTiO3 to improve its property, but the solid phase adulteration is not homogeneous and the expected improvements of the parameters for the component can not be achieved. Although a Sol-Gel method for adulterating BaTiO₃ has been reported in recent years, its wide use is limited by the high price of the materials. With the concept of Environmentally Benign Chemistry gradually accepted and the rapid development of electric industry, these traditional methods can't meet the need of the modem electronic industries. Study on the new method is very important for the need request of high quality. In my present work, a new method (low temperature solid state reaction) has been exploited to synthesize BaTiO₃. This method has many advantages, no solvents, no pollution and high yield.Firstly, a suitable amount of TICl₄ was slowly dropped to water solution under stirring. The pH value of the solution was adjusted to 7 by dropping ammonium hydroxide, H₂TiO₃ was formed. Then it was filtered and washed with double-distilled water until the Cl^- was't determined. Subsequently pure H₂TiO₃ was mixed with Ba(OH)₂·8H₂O. The mixture was ground for about several hours at room temperature, and then dried it at 120℃. At this moment, the BaTiO₃ phase was formed.Then we used this method to synthesize a series of BaTiO₃-based solid solution. Through trying different elements and review their effects on BaTiO₃, Sn and Sr are determined to be adulterated into BaTiO₃. With the effects of the ions, the capacity is enhanced obviously. Its dielectric constant is closed to 14000, but dielectric loss is only 0.03. From the experiment, I summarized and discussed the effects of ions and experiment conditions on material capacity.