Phase transition of nanophase ferroelectric PbTiO_3 ultrafine powder

With the development of optoelectronics, nanometer materials play a more and moreimportant role. Recent theoretical researches indicate that the nanosized semiconductorcrystallites demonstrate a high nonlinear optical susceptibility and a fast response speed.Studies on nanometer-sized particles are very active. Because of the multielements of chemi-cal composition and higher crystallization temperature, it is very difficult to preparenanosized ferroelectric particles through conventional ceramic method.

Sol-Gel Preparation and Phase Transition of RE Orthoborates

The rare earth berate YBO3 synthesized by sol-gel technique was found to be in two phases. However, the low-svmmetry form of YBO3 which was found also in some other rare earth (Sm, Eu, Gd) berates has a much different dependence on the preparing conditions, The photoluminescent spectra indicate that there are more than two sites for Eu3+ in the sol-gel prepared polycrystalline YBO3:Eu with low-symmetry.

纳米相铁电PbTiO_3超微粉的相变特性

通过溶胶－凝胶工艺和水解老化过程制备了纳米相钛酸铅（ＰｂＴｉＯ＿３）超微粉。经过ＸＲＤ分析精确地确定了晶格常数和晶粒尺寸。ＰｂＴｉＯ＿３超微粉的相变采用不同升温速率的ＤＳＣ分析和ＳＨＧ（ｓｅｃｏｎｄｈａｒｍｏｎｉｃｇｅｎｅｒａｔｉｏｎ）分析，得到了相变温度（ｏｎｓｅｔ温度）与晶粒尺寸的关系。结果表明：ＰｂＴｉＯ＿３的晶粒尺寸位于１０～１００ｍｍ范围，相变温度比体材料要低，并且相变区域被展宽。认为小晶粒尺寸可能是导致相变区域展宽的原因。最后将纳米相ＰｂＴｉＯ＿３微粉的相变与弛豫型铁电体的扩散相变（ｄｉｆｆｕｓｅｄｐｈａｓｅｔｒａｎｓｉｔｉｏｎ）进行了比较，并对超微粉的纳米结构、纳米相变和临界尺寸进行了讨论。

飞秒脉冲激光在铁电体中的冲击受激拉曼散射

将冲击受激拉曼散射应用于某些铁电体中 ,在时间域内分析物质晶格振动。τωα <2π是应用冲击受激拉曼散射的必要条件。使用钛宝石激光再生放大系统作为激发源 ,在LiTaO3 晶体内获得了声子电磁激元振荡模。将同种方法用于KDP ,在其铁电体相位转换点以上 5 0K的温度范围内 ,仅发现了波矢 q =6848cm- 1 ,弛豫时间常数τ0 =1 33× 10 - 1 3 s的弛豫振动软模 ,显示出KDP铁电体相位转换的弛豫特性。