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Study on the finite-size effects in ferroelectric thin films and fine-particles

铁电薄膜和细颗粒的有限尺寸效应研究

基本信息

批准号：
09450126
负责人：
ISHIKAWA Kenji
金额：
$ 2.11万
依托单位：
Shizuoka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1999
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09450126/
关键词：
ferroelectrics thin film fine-particle finite size effect surface relaxation PbTiOィイD23ィエD2 BaTiOィイD23ィエD2 low temperature growth 相転移 PZT レーザアブレーション

项目摘要

Finite size effects on the dielectric properties in ferroelectric materials were studied. Recently, the thickness of ferroelectric films is less than several tens of nanometer. Accordingly, the diameter of the particles in the film may be less than 10 nm. It is known that some dielectric properties differ from that of bulk materials when the size of crystallites approaches nano-meter size. However, the microscopic understanding of the size effect has not been obtained. In this research, we deal with the size effects on the phase transition in several perovskite type ferroelectrics.The first result concerns with the origin of the size effect on the phase transition. The size effects are successfully described by phenomenological theories based on the Landau-Ginzburg equation. The theory assumes the electric polarization near the surface is not uniform and differs from the bulk value. We found that the crystal lattices of lead titanate and barium titanate relaxes towards outside by X-ray measurements with the use of a simple model. We pointed out that the size effect should be caused by the non-homogenous polarization caused by the surface relaxation.We also studied the low-temperature growth of perovskite type ferroelectric films. If we can crystallize the film at low temperatures, we can obtain film composed of very small particles. The phase transition temperatures of such small particle should be lower than that of bulk crystals by the size effect. The dielectric constant of the film is expected to be larger than that of bulk material. We proposed a technique to insert a seeding layer between the film and the substrate. For example, insertion of PbTiOィイD23ィエD2 seeding layer made it possible to obtain a well crystallized film at very low temperature such as 450℃.

研究了铁电材料介电性能的有限尺寸效应。近年来，铁电薄膜的厚度已小于几十纳米。因此，膜中颗粒的直径可以小于10nm。众所周知，当微晶尺寸接近纳米尺寸时，某些介电性能不同于块体材料。然而，尚未获得对尺寸效应的微观理解。在这项研究中，我们研究了几种钙钛矿型铁电体中相变的尺寸效应。第一个结果涉及相变尺寸效应的起源。基于朗道-金兹堡方程的现象学理论成功地描述了尺寸效应。该理论假设表面附近的电极化不均匀并且与体积值不同。通过使用简单模型的 X 射线测量，我们发现钛酸铅和钛酸钡的晶格向外弛豫。我们指出尺寸效应应该是由表面弛豫引起的非均匀极化引起的。我们还研究了钙钛矿型铁电薄膜的低温生长。如果我们能够在低温下使薄膜结晶，我们就可以获得由非常小的颗粒组成的薄膜。由于尺寸效应，这种小颗粒的相变温度应该低于块状晶体的相变温度。薄膜的介电常数预计比块体材料的介电常数大。我们提出了一种在薄膜和基材之间插入晶种层的技术。例如，PbTiOィイD23ィエD2晶种层的插入使得可以在非常低的温度（例如450℃）下获得良好结晶的薄膜。