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

提出了一种以草酸钛钛酸钡为原料制备无杂质、无缺陷的钛酸钡纳米粒子的新方法。这种方法被称为两步热分解法，包括以下两个步骤：(1)步骤1：通过在空气中热分解草酸钛钛酸钡制备Ba2Ti2O5CO3中间化合物；(2)步骤：通过真空热分解Ba2Ti2O5CO3制备纳米BaTiO3。通过密度、杂质、TG-DTA、FT-IR、拉曼光谱、透射电子显微镜、拉曼光谱等多种测试手段对其进行了表征，结果表明所制备的BaTiO_3纳米粒子是无缺陷、无杂质、致密的。然而，没有办法测量颗粒的介电常数。由此，提出了一种新的粉末介电常数测量方法。粒度为17~1,000 nm BaTiO_3微粉的介电测量在一定的颗粒尺寸下，薄膜的介电常数最大。此外，具有最大介电常数的尺寸强烈依赖于制备方法。用原来的两步热分解法制备BaTiO_3微粉时，在70 nm处出现介电常数最大值15,000。另一方面，用改进的三步热分解法制备BaTiO_3微粉时，在140 nm处有最大介电常数5,000。为了验证这些高介电常数的有效性，用这些粒子制备了粒子/聚合物复合材料，并测量了它们的介电性能。结果表明，使用高介电常数制备的粒子/聚合物复合材料的介电常数总是比使用正常介电常数3,000制备的高得多。前者是在10℃~(-2)托尔真空中制备的，后者是在空气中制备的。用Rietveld方法对BaTiO_3粒子进行了结构修正，结果表明，BaTiO_3粒子总是由两部分组成：(A)表面立方层和(B)体四方层。此外，在10℃真空下制备的BaTiO_3纳米粒子的表面立方层厚度比在空气中制备的BaTiO_3纳米粒子的表面立方层厚度要薄得多。因此，为了解释这些差异，提出了一个基于“表面松弛”的新模型。此外，为了测量这些粒子的声子态，制备了表面光滑的三维胶体晶体，并测量了它们的远红外反射光谱。到目前为止，除了拉曼散射之外，还没有办法测量纳米粒子的声子态，但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，确定了不同纳米BaTiO_3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。较少

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