HP Laboratories, Long Down Avenue, Stoke Gifford, Bristol BS34 8QZ, UK.
Philos Trans A Math Phys Eng Sci. 2013 Mar 4;371(1988):20120253. doi: 10.1098/rsta.2012.0253. Print 2013 Apr 13.
In recent years, several papers reported an enhanced dielectric anisotropy when ferroelectric particles were suspended in a liquid crystal. These results seem to be sensitive to the liquid crystal used and the preparation method of the ferroelectric particles. In this paper, we compare different preparation methods of suspended barium titanate in two different liquid crystal hosts. As a control experiment, we followed similar preparation steps with non-ferroelectric silica particles. In all cases, we found a broadening of the optical Frederiks transition but no change in the dielectric anisotropy. Raman spectroscopy has been used to investigate the loss of tetragonal structure in the barium titanate as a function of milling time and particle size. As reported in the earlier literature, barium titanate does not exhibit a well-defined tetragonal crystal structure below a certain particle size and loses its ferroelectric features. This provides a simple rationalization for the absence of any dielectric enhancement.
近年来，有几篇论文报道称，当铁电粒子悬浮在液晶中时，介电各向异性会增强。这些结果似乎对所用的液晶和铁电粒子的制备方法很敏感。在本文中，我们比较了悬浮在两种不同液晶基质中的钡钛酸盐的不同制备方法。作为对照实验，我们用非铁电二氧化硅粒子遵循了类似的制备步骤。在所有情况下，我们都发现了光弗氏跃迁的展宽，但介电各向异性没有变化。拉曼光谱已被用于研究钛酸钡在研磨时间和粒径的作用下四方结构的损失。正如早期文献所报道的，钛酸钡的四方晶体结构在一定粒径以下不会表现出良好的定义，并且会失去其铁电特性。这为介电增强的不存在提供了一个简单的合理化解释。
