Nd：LiTaO3背散射组态下的喇曼光谱异常

本文研究了掺钕钽酸锂组体背射几何组态下的喇曼光谱，与纯钽酸锂晶体的喇曼光谱相比，发现喇曼谱中不仅有Ｅ（ＬＯ＋ＴＯ）模向Ａ１（ＴＯ）模的转变，而且还有新振动模的出现和部分振动模强度的变化，本文用光折变理论结合掺杂后晶体微观结构的改变对实验结果作了分析和探讨。     

Nd∶LiTaO_3背散射组态下的喇曼光谱异常

本文研究了掺钕钽酸锂晶体背散射几何组态下的喇曼光谱，与纯钽酸锂晶体的喇曼光谱相比，发现喇曼谱中不仅有Ｅ（ＬＯ＋ＴＯ）模向Ａ１（ＴＯ）模的转变，而且还有新振动模的出现和部分振动模强度的变化，本文用光折变理论结合掺杂后晶体微观结构的改变对实验结果作了分析和探讨．     

钽酸锂晶体的喇曼光谱及其方向色散的测定

为了测定钽酸锂铁电晶体异常声子的方向色散,我们找到一种较为满意的直角散射几何配置,制备了十个不同取向的样品,并为消除内反射光引起的附加散射,在样品表面上镀了增透膜,获得了波夫与光轴成不同夹角时的一系列寻常声子和异常声子的喇曼光谱.对这些喇曼光谱进行了识别,认定了四个A_1光学声子和九个E光学声子,确定了十三个异常声子方向色散支.由于全部异常声子的散射峰能始终一起出现在同一喇曼光谱中,使得异常声子方向色散的确定一目了然.最后用单轴晶体异常声子方向色散公式计算了异常声子的方向色散曲线,实验与理论计算相当符合.     

铌酸钡钠和钽酸锂铁电相变的实地观察

本文报道了用透射电子显微镜实地观察铌酸钡钠和钽酸锂铁电相变的实验结果。在室温电畴的尺寸为0.2—1μm。当温度增加到接近居里点时,形成准规则排列的微畴结构,其尺寸为几百埃,实验结果用稍微修正了的模型进行了解释。在钽酸锂中当接近铁电相变温度时,发现了强烈的辐照损伤,这可能跟相变的软模有关。 关键词：     

激光光散射作为铁电材料科学研究的工具

自1960年以来,激光非弹性光散射技术极为广泛地应用于材料科学的研究方面。喇曼光谱,布里渊光谱以及自关联光谱技术在铁电的有关领域获得了许多重要而新型的信息。本文将简要地评述这些技术的应用情况。     

激光光散射作为铁电材料科学研究的工具

自1960年以来,激光非弹性光散射技术极为广泛地应用于材料科学的研究方面。喇曼光谱,布里渊光谱以及自关联光谱技术在铁电的有关领域获得了许多重要而新型的信息。本文将简要地评述这些技术的应用情况。     

单模石英光纤中受激喇曼散射的研究

利用连续光纤激光器为泵浦源,对单模石英光纤中的受激喇曼散射进行了实验研究.在较低功率泵浦下,观察到由自发喇曼散射向受激喇曼散射演化的过程中,光谱不断变窄;当Stokes波信号功率较强时,观察到光谱峰值相对于泵浦波的频移量从440 cm－1转化到490 cm－1.在改进耦合系统后,不仅观察到一级喇曼频移,并且观察到了高阶Stokes光.在产生多级喇曼光谱时能量移动比较复杂,每两级的喇曼频移间隔并不完全相同.     

超声空化对丙酮激光喇曼光谱的影响

本研究设计了一种可吸入超声的喇曼光谱样品池,对丙酮的激光喇光曼谱的检测表明,超声空化降低了喇曼光谱的强度,我们认为,超声空化减少了激光光路上参与散射的丙酮分子数是光谱强度降低的主要原因。     

固体催化剂表面酸类型的激光喇曼光谱特性研究

本文对离子型固体如多相催化载体的表面酸类型进行了吸附态的激光喇曼光谱特性的研究。并对不同类型的固体样品进行了考查,对表面脱附净化方法作了改进。实现了原位(In-Situ)测定并和真空法作了比较,实验结果证明喇曼光谱是研究多相催化剂表面酸性能的一种较好的方法,它不但能严格的区分开吡啶的物理吸附和化学吸附,而且能区别开是吸附在Bronsted酸位上还是Lewis酸位上。对不同类型的载体,催化剂和分子筛进行了测定,所得结果和其催化性能很好的关联。     

LiNbO_3:Fe晶体的光折变对喇曼光谱的影响

我们观察到了LiNbO_3:Fe晶体中某些几何配置下十分异常的喇曼光谱现象。这一现象是与该晶体光折变后出现的异常光散射现象相联系的。     

Raman Spectra Study on LiTa0.9Nb0.1O3 Single Crystal

In this letter, Raman spectra of LiTa_0.9Nb_0.1O₃ single crystal in both of its ferroelectric phase and paraelectric phase are presented for the first time. Comparing with LiTaO₃ crystal, we find that the distribution and Raman shifts of normal vibrational mades are similar, but the line-shape and relative intensities of these modes have changed.     

On the universal regularities of the lattice dynamics in ferroelectrics

The main regularities revealed for the dynamic response in recent Raman spectroscopic investigations of ferroelectric crystals of the displacive type (LiNbO₃, LiTaO₃) and the order-disorder type (KDP, DKDP) are discussed. The characteristic feature of the dynamic response for all the crystals (KDP, DKDP, LiNbO₃, LiTaO₃) under investigation in the vicinity of the phase transition temperature is an intense central peak that follows from the theoretical predictions for the order-disorder phase transition. The possible factors responsible for the central peak, the character of the behavior of this peak outside the aforementioned temperature range, and the specific features of the behavior of the width and intensity of the central peak over a wide range of temperatures for order-disorder crystals are analyzed.     

Soft vibrational mode in LiNbO3 and LiTaO3

The temperature dependence of the far-infrared reflectivity as obtained with a scanning interferometer for the A₁- and E-type modes of both LiNbO₃ and LiTaO₃ is reported in the ferroelectric phase. Results of a Kramers-Kronig analysis are compared with Raman and neutron scattering data which are controversial about the existence of a soft vibrational mode. For LiTaO₃, spectra are obtained 300 K above the Curie temperature, in the paraelectric phase. The lowest-frequency A₁ (TO) mode is unambiguously found as soft and becomes rapidly overdamped.     

RAMAN SPECTROSCOPIC STUDY OF Nd-DOPED LITHIUM TANTALATE

Raman spectra of Nd-doped LiTaO₃ have been measured at right angle scattering geome-tries at room temperature. The spectra have drastically anomalous phenomena as compared with those of pure LiTaO₃. We may attribute these anomalies to the enhanced photoinduced refractive index change and the change of LiTaO₃ microstructure resulting from Nd doping.     

Absence of relaxor-like ferroelectric phase transition in (Pb,Sr)TiO3 thin films

We have performed dielectric and micro-Raman spectroscopy measurements in the 298–673 K temperature range in polycrystalline Pb_0.50Sr_0.50TiO₃ thin films prepared by a soft chemical method. The phase transition have been investigated by dielectric measurements at various frequencies during the heating cycle. It was found that the temperature corresponding to the peak value of the dielectric constant is frequency-independent, indicating a non-relaxor ferroelectric behavior. However, the dielectric constant versus temperature curves associated with the ferroelectric to paraelectric phase transition showed a broad maximum peak at around 433 K. The observed behavior is explained in terms of a diffuse phase transition. The obtained Raman spectra indicate the presence of a local symmetry disorder, due to a higher strontium concentration in the host lattice. The monitoring of some modes, conducted in the Pb_0.50Sr_0.50TiO₃ thin films, showed that the ferroelectric tetragonal phase undergoes a transition to the paraelectric cubic phase at around 423 K. However, the Raman activity did not disappear, as would be expected from a transition to the cubic paraelectric phase. The strong Raman spectrum observed for this cubic phase is indicative that a diffuse-type phase transition is taking place. This behavior is attributed to distortions of the perovskite structure, allowing the persistence of low-symmetry phase features in cubic phase high above the transition temperature. This result is in contrast to the forbidden first-order Raman spectrum, which would be expected from a cubic paraelectric phase, such as the one observed at high temperature in pure PbTiO₃ perovskite. PACS 78.30.-j; 77.80.Bh; 64.70.Kb; 68.55.-a; 77.22.-a; 77.55.+f     

Raman scattering in a ferroelectric sodium nitrite crystal

Raman spectra of the ferroelectric sodium nitrite are recorded over a wide spectral range at different temperatures, including the ferroelectric phase transition interval. The room-temperature Raman spectrum reveals the overdamped А₁(z) soft mode which is attributed to the ferroelectric phase transition.     

Nature of the ferroelectric-paraelectric phase transition in lithium tantalate

It is suggested that the ferroelectric phase transition in LiTaO₃ has characteristics of both displacement and order-disorder types, with peaks in the ion coordinate distribution function of the paraelectric phase at both centrosymmetric and off-center positions.     

Low temperature,high pressure Raman study of SbSBr

Abstract

We have measured the Raman spectra of the quasi-one-dimensional crystal SbSBr as a function of pressure at 295, 70, 37 and 25 K.

The pressure coefficients of the observed Raman modes have been determined and used to distinguish inter-from intrachain modes. Spectral features characteristic of the ferroelectric phase have been attributed to impurities or lattice imperfections and not to the presence of the ferroelectric phase, providing indication that the para-to ferroelectric phase transition occurs below 25 K.     

Relationship between phase structure and electrical properties of (K0.5Na0.5)NbO3-LiTaO3 lead-free ceramics

Lead-free piezoelectric ceramics of (1−x)K_0.5Na_0.5NbO₃-xLiTaO₃ (KNN-LT) system have been investigated in this work. X-ray diffraction, Raman spectra measurements, DSC (Differential Scanning Calorimetric), and dielectric constant versus temperature provide direct evidence that the phase transition temperature between tetragonal and orthorhombic shift to lower temperature with the increasing of LT content. The KNN-0.05LT ceramics exhibit the highest high-field d₃₃ up to 220 pm/V. At the same time, we also investigated the relationship between phase structure and electric properties, showing that the orthorhombic phase presents better piezoelectric temperature stabilities than the tetragonal phase. The result may provide a new way for KNN-based lead-free ceramics.