THz Region Dielectric Response and The Size Effect of Ferroelectric Microcrystallits

在这项研究中，我们的目标是明确铁电微晶的尺寸效应和太赫兹区介电响应的起源。为了实现这一目标，必须具备以下两点；(1)制备粒径为10 ~ 1000 nm的理想无缺陷钛酸钡微晶；(2)开发粉末介电测量方法，研究其在MHz频段频率和THz频段的介电响应。因此，通过本研究发现了以下四点。(1)建立了草酸钛钡的两步热分解方法，并利用该方法成功制备了粒径从17 nm到数百nm的无缺陷、无杂质钛酸钡微晶。(2)结合(A)钛酸钡悬浮液与有机溶剂的介电测量和(b)亚百万阶元有限元模拟，提出了一种测量粉末介电常数的方法，该方法成功地估计了粉末介电常数。(3)通过以上两者的结合，成功地消除了钛酸钡微晶对粒径的依赖。在粒径大于200nm的颗粒上，介电常数几乎恒定在3000左右。在200 nm以下，介电常数随粒径的减小而增大，在70 nm左右，介电常数在15000左右达到最大值。然后，在70 nm以下，介电常数随着粒径的减小而急剧减小，在17 nm处介电常数在100左右达到最小值。(4)利用这些钛酸钡微晶，通过改进的胶体外延法成功地形成了胶体晶体。利用钛酸钡微晶胶体晶体的远红外测量结果，成功地估计了介电响应在几太赫兹到几百太赫兹范围内。少

In this study, our objective is to clear an origin of a size effect and THz region dielectric response of the ferroelectric microcrystallites. For this objective, the following two points must be required; (I) preparation of ideal defect-free barium titanate microcrystallites with the particle sizes from 10 nm to 1000 nm, and (II) development of powder dielectric measurement method to study dielectric response at MHz region frequency and THz region. As a result, the following four points were found through this study. (1) A 2-step thermal decomposition method of barium titanyl oxalate was developed, and using this method, defect-free and impurity-free barium titanate microcrystallites were successfully prepared with particle sizes from l7 nm to several hundred nm. (2)By the combination between (a) the dielectric measurement using barium titanate suspension with organic solvent and (b) the simulation using a finite element method with submillion order elements, a powder dielectric measu … More rement method was developed, and this method succeeded to estimate the dielectric constants of the powders. (3) By the combination of the above two things, the size dependence on the particle sizes of barium titanate microcrystallites was successfully cleared. Above the prticles with sizes over 200 nm,the dielectric constants were almost constant at around 3000. Below 200 nm, the dielectric constants increased with the decreasing particle size, and at around 70 nm, the dielectric constant became to maximum around 15000. Then, below 70 nm, the dielectric constants decreased drastically with decreasing particle size, and at 17 nm, the dielectric constant became to minimum around 100. (4) Using these barium titanate microcrystallites, the formation of the colloidal crystals was succeeded by the modified colloidal epitaxy method. As the result of the far infra-red measurement using the colloidal crystals of barium titanate microcrystallites, the dielectric response was successfully estimated from a couple THz to a couple hundred THz region. Less