Ferroelectric microregion and photo-induced superparaelectricity

铁电微区和光致超顺电

基本信息

批准号：
17540289
负责人：
UWE Hiromoto
金额：
$ 2.3万
依托单位：
University of Tsukuba
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2005
资助国家：
日本
起止时间：
2005 至 2006
项目状态：
已结题

项目摘要

Magnetoresistance mobility has been measured by means of pulse photoconductivity measurements in KTaO_3 and SrTiO_3 at the temperature range below 100K. The employed method of the photoconductivity measurement for materials with high dielectric constant is based on an idea that we use both edges of several millimeters of the sample itself as blocking electrodes. Temperature variation of the magnetoresistance mobility coincides with the previous measured Hall mobility. For the measurements using long-wavelength light to excite electrons within a crystal, nonlinear conduction is observed above a moderately low electric field. For SrTiO_3, the streaming conduction is observed, in which drift mobility of electrons saturates with increasing field. The kinetic energy of the streaming electron is found to coincide with the energy of the ferroelectric soft phonon. For the stress induced ferroelectric phase transition, we also find the streaming motion of photo-induced carriers, in which kineti … More c energy of the streaming electron coincides with the energy of the ferroelectric soft phonon Eu to vanish at the ferroelectric transition. For KTaO_3, the saturation phenomenon of the drift mobility is not observed. Although belong to the same category of the quantum ferroelectric, electron-phonon interaction with ferroelectric soft phonon differs between them and the strength is bigger for SrTiO_3 than for KTaO_3. This seems to correspond to the fact that doped SrTiO_3 is superconductive at low temperatures but doped KTaO_3 is not. For the measurement with short-wave length light to investigate conduction in surface region in SrTiO_3, the magnetoresistance mobility is found to exhibit anomalies at temperatures of previous reported unusual behavior. We have also tried to prepare single crystals of SrTiO_3 with a good quality by the floating zone (FZ) method. When comparing with commercial crystals by the Bernouilli method, our FZ crystals with are found to have smaller etch-pit density and almost equal internal strains. However, the magnetoresistance mobility is found to be smaller than for crystals by the Bernouilli method. The Sr defect number for the FZ crystal seems to be larger than for Bernouilli crystals, which leads to the high scattering of photo carriers in FZ crystals Less

在低于100K的温度范围内，通过脉冲光电导测量KTaO_3和SrTiO_3来测量磁阻迁移率。高介电常数材料的光电导测量所采用的方法是基于我们使用几毫米的两个边缘的想法。对于使用长波长光激发的测量，磁阻迁移率的温度变化与之前测量的霍尔迁移率一致。对于晶体内的电子，在中等低的电场上方观察到非线性传导，对于SrTiO_3，观察到电子的漂移迁移率随着电场的增加而饱和。发现流动电子的动能与能量一致。对于应力引起的铁电相变，我们还发现了光致载流子的流动运动，其中流动电子的动能与的能量一致。对于KTaO_3，铁电软声子Eu在铁电转变时没有观察到漂移迁移率饱和现象，尽管它们与量子铁电体属于同一类别，但它们与铁电软声子的电子-声子相互作用有所不同。 SrTiO_3 的强度大于 KTaO_3，这似乎与掺杂的 SrTiO_3 在低温下具有超导性但掺杂的事实相对应。 KTaO_3 则不然。对于用短波长光测量来研究 SrTiO_3 表面区域的传导，发现磁阻迁移率在先前报道的异常行为的温度下表现出异常。通过浮区 (FZ) 方法获得良好的质量当与采用伯努利方法的商业晶体进行比较时，发现我们的 FZ 晶体具有更小的蚀坑密度和几乎相同的内部。然而，通过伯努利方法发现磁阻迁移率小于晶体，FZ 晶体的 Sr 缺陷数似乎大于伯努利晶体，这导致 FZ 晶体中光载流子的高散射。