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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℃.

研究了有限尺寸对铁电材料介电性能的影响。目前，铁电薄膜的厚度还不到几十纳米。因此，所述薄膜中的颗粒直径可小于10nm。众所周知，当晶体尺寸接近纳米尺寸时，某些介电性质与块体材料不同。然而，对尺寸效应的微观理解尚未得到。在本研究中，我们研究了几种钙钛矿型铁电体中尺寸对相变的影响。第一个结果与相变尺寸效应的起源有关。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。该理论假定近表面的电极化是不均匀的，与体值不同。通过x射线测量，我们发现钛酸铅和钛酸钡的晶格向外松弛。指出尺寸效应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。如果我们能在低温下使薄膜结晶，我们就能得到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低于体晶的相变温度。预计薄膜的介电常数要大于块状材料的介电常数。我们提出了一种在薄膜和衬底之间插入播种层的技术。例如,插入PbTiOィイc15ィエD2播种层能获得一个在非常低的温度下结晶膜如450℃。