BaTiO3晶体的各向异性散射

本文详细报道了对BaTiO_3晶体各向异性散射的观察结果。首次观察到一种由环和双曲线组成的散射图。利用光折变四波相互作用理论较圆满地解释了所观察的现象和实验结果。     

Pressure-Induced Phase Transition in BaTiO3 Nanocrystals

The crystal structure and electric properties of BaTiO3 nanocrystals are studied by in situ high-pressure synchrotron radiation x-ray powder diffraction. The phase transition takes place not only in the samples of BaTiO3 nanocrystals that are tetragonal phase with grain sizes more than 100nm, but also in the samples of BaTiO3 nanocrystals that are cubic phase with grain sizes less than 100nm. The pressures of phase transition are found to increase with decrease of the grain size from about 4 to 10GPa for crystallites ranging from 200 to 10nm in radius. The bulk moduli are calculated according to Birch-Murnaghan state equation before and after the phase transition.     

异型BaTiO3自泵浦相位共轭镜实验研究

本文首次演示了一种高效异型BaTiO_3自泵浦相位共轭镜,用该相位共轭镜的45°角和135°角切面获得其共轭反射率分别大于60％和40％,文中还给出了其它实验结果和结论。     

飞秒激光诱导玻璃内析出BaTiO3晶体

使用800nm、120fs、200kHz的高重复频率超短脉冲激光照射BaO-TiO2-SiO2系玻璃，玻璃经飞秒激光照射数秒钟后，激光会聚点的发光由800nm波长的红色突然转变为非常强的400nm的蓝色，对激光辐照点的发光光谱和X射线衍射分析表明，具有倍频效应的BaTiO3晶体已经产生。     

Dielectric Properties of Fine-Grained BaTiO3 Ceramics under High Pressure

We investigate the temperature dependence of the dielectric constant of BaTiO3 ceramic with coarse to nanograin size under different hydrostatic high pressures up to 5000 bar in the range between room temperature and 200℃. The ferroelectric-to-paraelectric phase transition temperatures Tc are determined from the peak of dielectric constant versus temperature. The values of average grain-size are estimated from the SEM images. It is found that the magnitude of dTc/dp varies considerably from sample to sample depending on grain size. The Curie point Tc of the sample with small grain size decreases more sharply than that of samples with larger one.     

钛原子位置对立方BaTiO3电子结构的影响

本文基于密度泛函理论(DFT)的第一原理方法,计算了Ti原子位置对BaTiO3电子结构的影响.Ti的位置变化导致晶格畸变,使电子结构发生变化;从能带结构、能态密度(DOS)、电子密度、Mulliken布居等计算结果分析表明,导带和价带主要由Ti的3d电子和O的2p电子,Ti原子位置的变化,使Ti的3d电子能量分布上移,而O的2p电子能量下移;Ti位置变化,Ti的3d电子与的sp电子形成的杂化轨道更趋向离子化,以致于使OI出现了正电荷,表明发生了的2p电子向Ti的转移;O原子电子的转移使得Ti原子在导带的3d电子能量降低,与O原子在价带的2p电子能量重叠,禁带消失;随着畸变程度提高,转移逐渐增强,使禁带宽度逐渐减小,直至完全消失.     

纳米BaTiO3陶瓷的Raman光谱研究

高压能增加陶瓷烧结的致密驱动力和抑制陶瓷晶粒的长大。用高压辅助烧结的方法得到了晶粒尺寸约为60和30 nm的致密纳米BaTiO3陶瓷。BaTiO3陶瓷的晶体结构随温度的变化由变温Raman光谱来研究。在温度范围-190℃到200℃内,与粗晶的BaTiO3陶瓷相比,纳米BaTiO3陶瓷Raman散射结果表明,随着晶粒尺寸的减小,Raman峰的强度变弱,相变越来越弥散,出现了相变峰的消失;而且随着温度的升高,在纳米BaTiO3陶瓷甚至在30 nm BaTiO3陶瓷中都有与粗晶相同的从三方相到正交相到四方相到立方相的连续相变。变温Raman散射也表明,当晶粒大小减小到纳米尺寸时,纳米BaTiO3陶瓷表现出与粗晶不同的新颖性质。在一定的温度范围内,存在多种铁电相的共存。     

Effect of Annealing on Ferroelectric Properties of Nanometre BaTiO3 Ceramics Prepared by High Pressure Sintering Method

Dense nanocrystalline BaTiO3 ceramics with a grain size of 5Onto are prepared under 6 GPa at 1273K using a high pressure sintering method. The sintered bulk is uniform and the relative density is above 97%. We anneal the ceramic samples in oxygen with various temperatures and for the annealing, several broadened peaks can be observed at different times without apparent grain growth. After about 378K（ by dielectric measurements. However, these peaks are very different from those of coarser-grained ceramics. It is indicated that both the elimination of oxygen vacancies and the release of residual stresses caused by high pressure greatly improve the overall ferroelectric properties of BaTiO3 ceramics. The observation of nearly linear polarization hysteresis loop after anneal provides the solid evidence of ferroelectricity in these nano-sized BaTiO3 ceramics. It is believed that the absence of 90° domains and the existence of poor-permittivity nonferroelectric grain boundaries contribute to the slim loop.     

四方相BaTiO3铁电性的第一性原理研究

在广义梯度近似下,利用超软赝势对立方相和四方相BaTiO3晶胞中Ti原子沿c轴位移时体系的能量、原子间电子云重叠布局数和各原子上的净电荷等进行了自洽计算.结果显示,当Ti原子沿c轴位移0.012nm时,四方相BaTiO3体系能量最低,其自发极化强度为0.261C/m2,该结果与实验数据相符合;同时表明,O原子的2p轨道和Ti原子的3d轨道的杂化是BaTiO3晶体出现铁电性的重要原因.     

掺铑BaTiO3单晶场致应变特性的研究

系统地研究了掺铑的BaTiO3单晶在老化后的场致应变性能.研究发现,晶体的场致应变随老化时间的增加而增大,在老化27天后,在300V/mm的电场下,其双向场致应变可达1.11%;在较小的测试频率下(0.01Hz)也可得到0.95%的可逆的巨大的单向场致应变,在低频范围内,晶体的单向场致应变随测试频率增大而减小;研究晶体老化后的电滞回线,发现其形状类似于蜂腰磁滞回线.实验结果表明,对BaTiO3单晶掺杂铑元素可以大大改善其电致伸缩性能,可能产生新的在超大应变及非线性驱动器中的应用.     

Laser Molecular Beam Epitaxy Growth of BaTiO3 in Seven Thousands of Unit-Cell Layers

BaTiO3 thin films in seven thousands of unit-cell layers have been successfully fabricated on SrTiO3 （001） substrates by laser molecular beam epitaxy. The fine streak pattern and the undamping intensity oscillation of reflection high-energy electron diffraction indicate that the BaTiO3 film was layer-by-layer epitaxial growth. The measurements of scanning electron microscopy and atomic force microscopy show that surfaces of the BaTiO3 thin film are atomically smooth. The measurements of x-ray diffraction and transmission electron microscopy, as well as selected-area electron diffraction reveal that the BaTiO3 thin film is a c-oriented epitaxial crystalline structure.     

过渡族元素掺杂BaTiO3-Tb1-xDyxFe2-y层状复合材料中的磁电效应

用溶胶-凝胶法制备1.0%mol Mn,Cr,Co掺杂BaTiO3(BTO)粉体,在1350℃下烧结成多晶陶瓷样品.X射线衍射和差示扫描量热分析表明,室温下掺杂BaTiO3具有四方钙钛矿结构;居里点和相变潜热随Cr,Mn,Co掺杂逐渐降低.将掺杂BaTiO3与Tb1-xDyxFe2-y(TDF)胶合制成双层磁电复合材料,并研究了Cr:BTO-TDF,Mn:BTO-TDF,Co:BTO-TDF层状复合材料中的磁电效应.实验表明,在340×80 A·m-1偏置磁场下,Cr:BTO-TDF的横向磁电电压系数达到最大值586 mV·cm-1·(80 A·m-1-1.在400×80 A·m-1偏置磁场下,Mn:BTO-TDF和Co:BTO-TDF的横向磁电电压系数的最大值分别为480 mV·cm-1·(80 A·m-1-1和445 mV·cm-1·(80 A·m-1-1.研究表明掺杂BaTiO3-TDF层状复合材料中具有较强的磁电耦合.作为无铅压电材料,掺杂BaTiO3制备的磁电效应器件颇具应用前景.     

相方相BaTiO3及BaTiO3：Ge的拉曼散射特性研究

本文报道了在室温下ＢａＴｉＯｅ及ＴｉＯ３：Ｃｅ的拉曼谱的特点，着重讨论了前向散射配置下两个Ａ１（ＴＯ）模（位于２７５ｃｍ＾－１和５１６ｃｍ＾－１左右）出现在Ａ１（ＴＯ）谱中的原因，通过设计特别的前向散射实验得到了此配置下由于晶体出射两对入射光的反射造成的背向散射的强度。在ＢａＴｉＯ３的前向散射谱中扣除了背向散射面对人入射光的反射造成的背向散射的强度。在ＢａＴｉＯ３的前向散射谱中扣除了背向散射信号后     

积分球腔内BaTiO3：Ce晶体的自泵浦相位共轭增强现象的观测

报道了聚四氟乙烯积分球腔内光折变晶体ＢａＴｉＯ３：Ｃｅ在Ｈｅ－Ｎｅ激光作用下产生自泵浦相位共轭的增强现象，并对实验结果进行了分析。     

Ce∶BaTiO3中光折变光栅衍射效率上升现象及分析

在对Ce∶BaTiO3晶体进行双光束干涉光折变光栅暗衰减特性的实验研究中,发现了暗条件下光折变光栅归一化衍射效率长时间上升的异常现象：在e光偏振、大入射角度产生光折变光栅的实验中,衍射效率在长逾8 h的时间内持续上升.而在e光干涉、小入射角度和o光干涉时均未出现衍射效率长时间上升的现象.分析认为：由于自泵浦位相共轭光的产生和晶体中的两个深能级参与了光折变过程,形成了衰减速度不同、光栅方向垂直的两个光栅,导致了暗衰减时衍射效率的长时间上升.     

Co／BaTiO3纳米复合薄膜的PLD法制备

纳米金属一陶瓷复合薄膜是纳米金属颗粒嵌埋在介质载体中形成的一种复合材料。在此体系中纳米金属的小尺寸效应、表面界面效应、量子尺寸效应、量子隧穿效应及陶瓷基体的高介电常数及介电强度，赋予此体系独特的光学特性。如高的三阶非线性光学极化率、超快的三阶非线性响应时间及高三阶非线性系数等，在电子器件和光学材料方面有着潜在的应用前景，引起了国内外学者的极大兴趣。