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

铁电材料对非电性能的有限尺寸影响已被研究。最近，铁电薄膜的厚度比纳米计的几个十倍还少。确切地说，电影中粒子的直径可能小于10纳米。这是众所周知的，因为当晶体的尺寸接近纳米尺度时，晶体材料的尺寸从块状材料中分离出来。However，对尺寸的微观理解，但并没有被发现。在这项研究中，我们确定了几种Perovskite型铁电子的尺寸影响，第一个结果与相位过渡的尺寸影响起源有关。根据兰道-金茨堡方程，尺寸效应被成功地描述为基于现象学理论的大小效应。理论的假定是，表面附近的电极化并不统一，也不符合散装值的差异。我们发现了一种简单模型的使用中的铅钛和钡钛合金的晶体晶格，通过X射线测量来实现外部放松。我们指出了尺寸效应应该被表面放松所导致的非同源极化所导致的，我们也研究了perovskite型铁电薄膜的低温度增长。如果我们能在低温下冻结电影，我们就能用非常小的粒子制作电影。这种小颗粒的相位转换温度应该低于体积晶体的大小效应。“电影的非线性常数是预期的，比大块材料要大。”我们提出了一种技术来插入电影和底层之间的种子层。For example， insertion of PbTiOイイD23イエD2 seeding layer made it possible to obtain a well crystallized film at very low temperature such as 450℃。

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℃.