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

提出了一种以草酸钛钡为原料制备无杂质、无缺陷钛酸钡纳米颗粒的新方法。该方法称为两步热分解法，由以下两步组成：即(1)1^<st>步骤：通过草酸钛钡在空气中热分解制备Ba_2Ti_2O_5CO_3的中间化合物；(2)2^< and >步骤：通过Ba_2Ti_2O_5CO_3在真空中热分解制备BaTiO_3纳米颗粒。通过密度、杂质、TG-DTA、FT-IR、拉曼、TEM、拉曼等多种测量方法对纳米BaTiO_3进行了表征，结果表明纳米BaTiO_3具有无缺陷、无杂质、致密等特点。然而，没有办法测量粒子的介电常数。从而为粉末介电常数的测量提供了一种新的方法。对17 ~ 1000 nm的BaTiO_3细颗粒进行粉末介电测量，得到了一定粒径下的最大介电常数。此外，最大介电常数的尺寸与制备方法密切相关。采用原始的两步热分解法制备BaTiO_3细颗粒时，在粒径为70 nm处的介电常数最大值为15000。另一方面，当采用改进的三步热分解法制备BaTiO_3细颗粒时，在140 nm处的介电常数最大可达5000。为了证实这些高介电常数的有效性，用这些粒子制备了颗粒/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颗粒/聚合物复合材料的介电常数始终高于使用正常介电常数3,000制备的颗粒/聚合物复合材料。前者在10^<-2>的真空条件下制备，后者在空气中制备。采用Rietveld法对BaTiO_3颗粒进行结构细化，发现所有BaTiO_3颗粒始终由两部分组成；(a)表面立方层(b)块状四边形层。此外，在10^<-2> torr的真空条件下制备的BaTiO_3纳米颗粒的表面立方层厚度比在空气中制备的BaTiO_3纳米颗粒薄得多。因此，为了解释这些差异，提出了一种基于“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。迄今为止，除了拉曼散射之外，没有办法测量纳米粒子的声子态，但利用三维胶体晶体，获得了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纳米粒子的软模频率。结果表明，BaTiO_3粒子的介电常数随软模频率的降低而增大。软模频率的减小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