SYNTHESIS OF NANOSTRUCTURED TRANSPARENT BaTiO_3 CERAMICS WITH NOVEL ELECTRONIC AND OPTICAL PROPERTIES

本研究的目的是通过高浓度溶胶-凝胶处理，建立一种具有新型电子和光学性能的纳米结构透明（或半透明）钛酸钡陶瓷，这是我们独立开发的一项重要创新。结果如下：1)透明BaTiO_3整体凝胶的合成：以1.0 mol/L的高浓度Ba、Ti烷氧化物溶液为原料，在0℃下水蒸气水解，30 ~ 500℃陈化数天，成功地合成了透明BaTiO_3整体凝胶。根据水解水用量和水解温度对凝胶性能的影响，定量表征凝胶的结晶程度和孔隙结构。2)澄清了BaTiO_3纳米晶allites的形成机理：发现纳米晶allites BaTiO_3颗粒，当使用足够的水解水时，更多的是由前驱体溶液直接形成的。3)透明凝胶的孔隙结构和光学性质分析：利用N_2吸解吸孔率仪表征了透明BaTiO_3凝胶的孔隙结构，在3 ~ 10nm范围内具有狭窄的孔隙分布。由于尺寸效应的影响，BaTiO_3晶体的光学吸收边缘比块状BaTiO_3晶体的光学吸收边缘要大。4)半透明BaTiO_3陶瓷的制备：在O_2气氛下，在1100℃下烧结具有特定孔隙结构的透明凝胶，成功制备出半透明BaTiO_3陶瓷，该凝胶表现出不同寻常的致密化行为，在500℃以下的低温下开始显著致密化。5)半透明BaTiO_3陶瓷的介电性能和光学性能表征：测量了亚微米级晶粒尺寸的半透明BaTiO_3陶瓷的介电性能。发现半透明陶瓷具有铁电特性，在居里温度下有明显的介电峰，在室温下有明确的磁滞回线。对于大晶粒尺寸的半透明BaTiO_3陶瓷，观察到明显的光散射电光效应，但不幸的是，由于目前的半透明BaTiO_3陶瓷的晶粒尺寸大，没有观察到由于尺寸效应而产生的新的光学性质。少

The objective of this study is to establish a procedure nanostructured transparent (or translucent) barium titanate ceramics with novel electronic and optical properties by high concentration sol-gel processing, which was individually developed by us, to introduce an important innovation in the field of electroceramics.The obtained results are summarized as follows :1) Synthesis of transparent BaTiO_3 monolithic gels : We succeeded in synthesizing transparent BaTiO_3 monolithic gels from highly concentrated Ba, Ti alkoxides solution (1.0 mol/L) by hydrolyzing with water vapor at 0℃, followed by aging for several days at 30-500℃. The gel's properties, including the degree of crystallization and pore structure, were characterized quantitatively on the basis of the influenced of the amount of hydrolysis water and the hydrolysis temperature upon the properties.2) Clarification of the creation mechanism of BaTiO_3 nanocryst allites : It has been found that nanocryst alline BaTiO_3 particles … More are formed directly from the precursor solution when a sufficient amount of hydrolysis water is used.3) Analysis of the pore structure and optical properties of transparent gels : Using an N_2 absorption-desorption porosimeter the pore structure of transparent BaTiO_3 gels has been characterized to have a narrow distribution of pores in the range of 3 to 10nm. The optical absorption edge of the cryst alline BaTiO_3 particles was found to be larger than that of bulk Batio_3 crystal due to probably the size effect.4) Preparation of translucent BaTiO_3 ceramics : We succeeded in producing translucent BaTiO_3 ceramics by sintering transparent gels with a specific pore structure at 1100℃ in an O_2 at mosphere, which gels showed an unusual densification behavior that is characterized by a significant densification starting at a low temperature below 500℃.5) Characterization of dielectric and optical properties of translucent BaTiO_3 ceramics : The dielectric properties of translucent BaTiO_3 ceramics with sub-micrometer grain sizes have been measured. The translucent ceramics have been found to exhibit ferroelectric properties, which was demonstrated by a distinct dielectric peak at the Curie temperature and a well-defined hysteresis loop at room temperature. A distinct electro-optic effect of light scattering was observed for a large grain-sized translucent BaTiO_3 ceramic, though, unfortunately, novel optical properties due to the size effect was not observed for the present translucent BaTiO_3 ceramics because of their large grain sizes. Less