THz Region Dielectric Response and The Size Effect of Ferroelectric Microcrystallits

在这项研究中，我们的目标是弄清铁电微晶的尺寸效应和THz区介电响应的来源。为实现这一目标，必须做好以下两个方面的工作：(1)制备理想的无缺陷钛酸钡微晶，其粒径在10~1000 nm之间；(2)发展粉末介电测量方法，研究其在MHz和THz频段的介电响应。因此，通过本研究发现了以下四点。(1)提出了草酸钛钛酸钡的两步热分解法，并利用该方法成功地制备了颗粒尺寸在17 nm~数百nm之间的无缺陷、无杂质的钛酸钡微晶。(2)通过(A)有机溶剂钛酸钡悬浮液介电测量与(B)亚百万阶单元有限元模拟相结合，提出了一种粉末介电测量方法…提出了一种新的估算粉末介电常数的方法，并成功地估算了粉末的介电常数。(3)通过以上两方面的结合，成功地解决了钛酸钡微晶的尺寸依赖关系。在尺寸大于200 nm的颗粒上方，介电常数几乎不变，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，介电常数随着颗粒尺寸的减小而急剧下降，在17 nm处，介电常数在100左右达到最小值。(4)用改进的胶体外延法制备了钛酸钡微晶。利用钛酸钡微晶胶体晶体的远红外测量结果，成功地估计了从几太赫兹到几百太赫兹的介电响应。较少

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