Preparation of Nanopartide-dispersed Hybrid-Polymer Nonlinear Optoelectronic Materials and Phase Control

提出了一种以草酸钛氧钡为原料制备无杂质、无缺陷钛酸钡（BaTiO_3）纳米粒子的新方法。该方法被称为两步热分解法，并且由以下两个步骤组成;即，(1)1（<st>2）真空热分解<nd>Ba_2Ti_2O_5CO_3制备BaTiO_3纳米粒子。通过密度、杂质、TG-DTA、FT-IR、拉曼、TEM、拉曼等测试手段对所制备的BaTiO_3纳米粒子进行了表征，结果表明所制备的BaTiO_3纳米粒子无缺陷、无杂质、致密。然而，没有办法测量颗粒的介电常数。因此，一种新的粉末介电常数的测量方法是新开发的。对17 ~ 1000 nm的BaTiO_3微粉的粉末介电性能进行了测试，结果表明：BaTiO_3微粉的介电常数随BaTiO_3含量的增加而增加; ...更多信息 在一定的颗粒尺寸下导致最大介电常数。此外，具有最大介电常数的尺寸强烈依赖于制备方法。当使用原始的两步热分解法制备BaTiO_3细颗粒时，在70 nm的颗粒尺寸处观察到介电常数最大值为15，000。另一方面，当使用改进的三步热分解法制备BaTiO_3细颗粒时，在140 nm处观察到介电常数最大值为5，000。为了证实这些高介电常数的有效性，制备使用这些颗粒的颗粒/聚合物复合材料，并测量这些介电性能。结果，使用高介电常数的颗粒/聚合物复合物总是显示出比使用正常介电常数3，000制备的那些高得多的介电常数。前者在10 ℃真空中制备<-2>，后者在空气中制备。用Rietveld方法对BaTiO_3颗粒的结构进行了细化，发现BaTiO_3颗粒总是由两部分组成：（a）表面立方层和（B）体相四方层。在10 μ m真空中制备的BaTiO_3纳米粒子的表面立方层厚度<-2>比在空气中制备的BaTiO_3纳米粒子的表面立方层厚度薄得多。因此，为了解释这些差异，提出了一个新的模型的基础上“表面弛豫”。此外，为了测量这些粒子的声子状态，制备了具有光滑表面的3D胶体晶体，并测量了它们的远红外反射光谱。迄今为止，除了拉曼散射外，还没有其他方法来测量纳米颗粒的声子态，但是使用三维胶体晶体，可以获得清晰的远红外反射光谱。通过对这些光谱的分析，确定了各种BaTiO_3纳米颗粒的软模频率。结果表明，BaTiO_3颗粒的介电常数随软模频率的降低而增大。此外，软模频率的降低与表面立方层的厚度密切相关。少

A new preparation method was proposed to prepare impurity-free, defect-free barium titanate (BaTiO_3) nanoparticles using barium titanyl oxalate. This method was called a 2-step thermal decomposition method, and composed of the following two steps ; i.e., (1)1^<st> step : a preparation of intermediate compound of Ba_2Ti_2O_5CO_3 by thermal decomposition of barium titanyl oxalate in air and (2) 2^<nd> step : a preparation of BaTiO_3 nanoparticles via thermal decomposition of Ba_2Ti_2O_5CO_3 in vacuum. As the results of characterization using many kinds of measurements such as density, impurity, TG-DTA, FT-IR, Raman, TEM observation, Raman and so on, it was cleared that these BaTiO_3 nanoparticles were defect-free, impurity-free, and dense. However, there was no way to measure dielectric constant of particles. Thus, a new measurement method for powder dielectric constants was newly developed. The powder dielectric measurement of BaTiO_3 fine particles with sizes from 17 to 1,000 nm revea … More led the maximum dielectric constant at a certain particle size. Moreover, the sizes with maximum dielectric constants were strongly dependent on the preparation methods. When the BaTiO_3 fine particles were prepared using the original 2-step thermal decomposition method, a dielectric constant maximum of 15,000 was observed at 70 nm particle size. On the other hand, when the BaTiO_3 fine particles were prepared using the modified 3-step thermal decomposition method, a dielectric constant maximum of 5,000 was observed at 140 nm. To confirm the validity of these high dielectric constants, particle/polymer composite using these particles was prepared and these dielectric properties were measured. As the result, the particle/polymer composite using the high dielectric constant showed always much higher dielectric constants than those prepared using the normal dielectric constant of 3,000. The former BaTiO_3 was prepared in vacuum of 10^<-2> torr while the latter BaTiO_3 was prepared in air. Structure refinement of BaTiO_3 particles using a Rietveld method revealed that all of BaTiO_3 particles were always composed of two parts ; (a)surface cubic layer and (b)bulk tetragonal layer. Moreover, a thickness of surface cubic layer for BaTiO_3 nanoparticles prepared in vacuum of 10^<-2> torr was much thinner than that for BaTiO_3 nanoparticles prepared in air. Thus, to explain these differences, a new model on the basis of "surface relaxation" was proposed. Moreover, to measure phonon state of these particles, 3D colloidal crystals with a smooth surface were prepared, and their far infrared reflection spectra were measured. To date, there was no way to measure phonon state of nanoparticles except for Raman scattering, but using the 3D colloidal crystals, the clear far infrared reflection spectra were obtained. By the analysis of these spectra, soft mode frequency was determined for various BaTiO_3 nanoparticles. As the result, it was cleared that the dielectric constant of BaTiO_3 particles increased with decreasing soft mode frequency. Moreover, the decrease of soft mode frequency was strongly related to the thickness of surface cubic layer. Less