化学计量比LiNbO3晶体的畴结构及完整性研究

本文对用助熔剂提拉法生长的两种化学计量比LiNbO3晶体进行了测试分析,并与同成分LiNbO3晶体相比较.通过差热分析和X射线粉末衍射测试,得出随着晶体中Li2O含量的增加,其居里温度变高,晶格常数变小.用酸腐蚀晶体,通过直接观察和金相照片,分析其畴结构,得出SLN11是单畴生长,首次观察出SLN19晶体在Z切面上出现了三块面积较大的对称反畴区,将其称为区域性单畴.另外,还对晶体在(001)方向抛光面的不同位置测量了其回摆曲线,得到了其中SLN19晶体有着较完整的结晶面.期望通过改变生长参数,长出完全单畴且更加接近化学计量比的LiNbO3晶体.     

三元铁电单晶Pb(Yb1/2Nb1/2)O3-Pb(Zn1/3Nb2/3)O3-PbTiO3生长及性能表征

采用高温助熔剂法首次成功生长出了Pb(Yb1/2Nb1/2) O3-Pb(Zn1/3Nb2/3) O3-PbTiO3 (PYZNT)三元铁电单晶,并对晶体组分、介电、铁电和压电性能进行了研究.结果表明,晶体为纯三方钙钛矿相,实际组分为0.68PYN-0.22PZN-0.1PT.分别对晶体的介电,铁电和压电性能进行研究.介电常数ε'和介电损耗tanδ对温度和频率表现出典型的弛豫行为.晶体的居里温度TC为80℃.由于反铁电体PYN含量较高,晶体具有非常大的矫顽场,在100kV/cm的外电场条件下极化还不能反转,因而无法得到饱和的电滞回线.在未极化条件下,测得晶体的压电常数d33为78 pC/N.     

La3+掺杂对Pb(Lu1/2Nb1/2)O3反铁电单晶储能性能的影响

采用顶部籽晶法生长了La3+掺杂Pb(Lu1/2Nb1/2)O3(PLN)反铁电单晶,晶体组分简写为xLa-PLN(x=1;、3;、5;),并详细研究了La3+掺杂对PLN晶体储能性能的影响.通过ICP测试了不同配比晶体的实际掺杂比例,分别为0.3;、1.1;、2.9;.XRD显示该晶体体系为正交相钙钛矿结构,且存在两套超晶格衍射点阵,分别由A位铅离子反平行排列和B位离子有序排列导致.介电温谱给出了晶体的介电常数、介电损耗随温度和频率的变化规律,不存在弥散相变.变温电滞回线显示,该体系均表现出典型的双电滞回线特性,且随着La3+含量的增加,有效储能密度逐渐增大,最高储能密度达到5.1 J/cm3.这主要是由于La3+掺杂导致体系的容忍因子下降,从而增强了反铁电稳定性,最终提高了PLN体系的能量存储密度.     

四方相区NBT-KBT无铅铁电介电弛豫与铁电相变研究

本文研究了具有四方结构的(Na1-xKx)0.5Bi0.5TiO3体系中x＝0.22,0.26和0.30陶瓷材料不同温度下的电滞回线,结合变温XRD和介电温谱分析,发现该体系四方结构的组成为反铁电体,但紧靠准同型相界的四方结构由于场诱导下引起的反铁电-铁电相变,表现出铁电体特性,材料在升温过程中由于反铁电宏畴向微畴的转变导致了介电峰的产生,且在介电温谱上表现出强烈的介电常数-频率依赖性,为弛豫铁电体特征.     

近化学计量比LiNbO3晶体各向畴形态的研究

本文对采用双坩埚提拉法生长的近化学计量比LiNbO3晶体沿其各向切块腐蚀后通过直接观察和在金相显微镜下观察,对其各个面的畴结构进行了分析.我们发现晶体a面上由于镜相对称不反映畴结构,b面和c面上的腐蚀形貌则完全显露而且按一定的方向整齐地排列,证明我们生长的SLN晶体是完全单畴结构的晶体.     

高分辨X射线衍射术对NdP5O14晶体的自发应变及铁弹畴结构的研究

利用助溶剂法,已经生长出15mm×25mm×60mm的大尺寸NdP5O14(NPP)晶体.用高分辨X射线衍射术对自发应变及铁弹畴结构进行了研究.对几个不同的反射,可在其摇摆曲线上观测到由基体畴和铁弹畴之间的取向差导致的反射峰的分离.通过反射峰分离的特点,可以确定铁弹畴结构.NPP晶体中大多数铁弹畴为a型畴,b型畴只出现在严重形变的区域. 基于NdP5O14晶体畴结构,我们分别计算了802,402和204反射的峰分离量.实验测量结果符合计算结果.另外,通过测量基体畴和铁弹畴的800反射的峰分离量我们确定了NdP5O14的自发应变是0.0082.通过结构和对称性分析,我们对这种晶体的畴结构进行了详细讨论.     

弛豫铁电晶体PZNT(001)晶面的腐蚀行为

采用化学腐蚀方法研究了坩埚下降法生长的PZNT93/ 7晶体(001)晶面的腐蚀行为.在PZNT晶体表面观察到反平行180°原生态铁电畴,在抛光样品表面观察到位错蚀坑、包裹物、机械加工划痕等缺陷形貌,并对腐蚀机理进行了探讨.化学腐蚀还揭示了微观畴的动力学变化,显示畴结构对环境变化十分敏感.     

基于偶极子翻转理论的铁电薄膜电滞回线模型

结合铁电体的宏观特性及微观特性,基于偶极子翻转理论(DST),将偶极子翻转的概率函数进行傅里叶展开,建立了一个铁电薄膜电滞回线模型.运用该模型对不同的电滞回线进行模拟,模拟结果与实验结果具有很好的一致性.该模型表达式简洁,参数少且易计算,具有普遍适用性.     

双掺杂TGS晶体——LUTGS

分别在58～54℃和45～38℃温区生长了完整的LUTGS单晶.揭示了两种晶体的生长习性.通过对两种晶体电滞回线、介电、热释电性能的测量,发现两温区生长的LUTGS单晶的热释电材料优值M(P/ε)无大差异,但都比纯TGS有显著提高.     

氟化钡晶体电注入着色

在不同的温度,电压和时间条件下,经点阴极电注入,有效地使氟化钡晶体着色.在室温下,分别对着色前后的晶体进行系统光谱测量.在着色前的氟化钡晶体中未观测到明显的吸收峰.在着色后的氟化钡晶体中,观测到大量的F和FA色心以及一些未知色心.对不同电注入温度、电压和时间条件下的着色氟化钡晶体光谱进行比较分析,得到了经点阴极电注入着色氟化钡晶体色心强度随着色温度,电压和时间的变化规律并给出了色心形成机理以及色心强度随温度、电压和时间变化机理.     

Growth and dielectric properties of Ta2O5 single crystal by the floating zone method

Large Ta₂O₅ single crystal with high‐dielectric permittivity was successfully grown by floating zone (FZ) method under air atmosphere. The grown crystal that has been obtained was typically about 8 mm in diameter and 90 mm in length. The crystal growth parameters were optimized. The crystal symmetry, characterized by means of X‐ray diffraction (XRD), was found to be tetragonal. The relative permittivity and loss tangent along growth and [001] direction were measured in the temperature range between ‐200 °C and 200 °C, which showed a strong dielectric anisotropy. At a frequency of 1 MHz and 20 °C, the dielectric permittivity along the growth direction and [001] direction are 81.17 and 25.04 respectively. The stabilization of high‐temperature phase can explain the dielectric enhancement.     

Low‐temperature elastic and dielectric properties of K3Na(SO4)2 crystals

Elastic and dielectric properties of glaserite K₃Na(SO₄)₂ single crystal were examined using the method of composite oscillators, Brillouin light scattering methods and dielectric spectroscopy. Measurements were performed in the temperature range from 18 K to 300 K. Anomalies in the temperature dependencies of Brillouin shift and dielectric permittivity at about 70 K confirmed the earlier predicted phase transition at 75 ± 25 K. Temperature dependences of the resonance frequency of the vibrating composite oscillator, Brillouin shift measured in the [110] direction, components of dielectric permittivity tensor reveal an anomaly at about 50 K. Moreover, thermal hysteresis of the dielectric permittivity suggested the presence of an incommensurate state between T ₁ = 50 K and T ₂ = 70 K. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

高质量直径180mm氟化锂晶体的生长

通过对晶体原料的提纯及生长工艺条件的优化,采用改进的坩埚下降法成功地制备出直径达到180mm的高质量氟化锂单晶.晶体的透过率在0.2～6.5 μm波长范围内最高透过率约为94;.     

Accurate Modelling of Liquid Crystal-Based Microwave Devices

Liquid crystal substrates have been shown to provide the means to develop low-cost, reconfigurable, adaptive and tuneable microwave devices for mobile and wireless communication systems. In order to take maximum advantage of the possibilities that these materials offer and to design LC-based devices appropriately, techniques for the characterisation of the liquid crystal dielectric properties are needed. Similarly, appropriate modelling methods are required to simulate accurately the switching behaviour of the liquid crystal and the characteristics of the wave propagation through the devices, taking full consideration of the point-by-point variation of the material tensor permittivity.     

Growth and characterization of L‐histidine hydrochloride monohydrate single crystals

Good optical quality single crystal of L‐histidine hydrochloride monohydrate (LHC) a novel semi organic NLO material was grown by slow solvent evaporation technique. The crystal was characterized by X‐ray diffractometry (XRD), Fourier Transform Infra‐red (FTIR), UV‐Vis‐NIR, TGA, DTA, microhardness and solubility studies. The SHG efficiency is found to be higher than that of KDP crystal. The dielectric constant and dielectric loss of the crystal was studied as function of frequency and the results are discussed. Photoconductivity studies were also carried out which reveals the positive photoconducting properties of the sample. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electron microscopy study of an Old Russian (XII century) encolpion cross with black inlay

The phase compositions of the basic material (alloy) of a pre-Mongolian Old Russian encolpion cross found near Suzdal and its black inlay have been investigated by methods of scanning and transmission electron microscopy and energy-dispersive X-ray microanalysis. The cross material is lead–zinc–tin α-bronze, and the black is copper sulfide with lead inclusions. As a result of the corrosion, tin and copper oxides and zinc sulfides, which made the cross dark gray, were formed on its surface. It is shown that the corrosion depth is as large as 50 μm; thus, laps must be prepared to accurately determine the morphology and phase composition of the corrosion layer. Decoration with black was apparently performed by pouring with copper sulfide melt or melting a powder preliminarily placed in grooves forming an image on the surface.     

双温区热扩散掺杂Fe2+∶ZnSe激光晶体的制备及激光输出性能

本文以CVD ZnSe晶片为基质材料,以FeSe粉末为掺杂物,采用双温区热扩散掺杂技术获得了尺寸为Ø22 mm×4 mm的Fe²⁺∶ZnSe激光晶体。通过二次离子质谱(SIMS)测试该晶体样品表面铁离子浓度为3.43×10¹⁸ cm^-3,并通过X射线光电子能谱(XPS)分析了晶体样品中铁元素的离子价态。采用UV/Vis/NIR分光光度计和傅里叶红外光谱仪测试了Fe²⁺∶ZnSe激光晶体的透过谱图。测试结果显示,在3.0 μm处出现了明显的Fe²⁺吸收峰,峰值透过率为5.5%。以波长为2.93 μm的Cr, Er∶YAG激光器为泵浦源,温度77 K时抽运尺寸10 mm×10 mm×4 mm的 Fe²⁺∶ZnSe晶体,获得了能量为191 mJ、中心波长4.04 μm的中红外激光输出,光光转换效率13.84%。     

Dielectric relaxation of (N(C2H5)4)2CoCl2Br2 nanocrystallites incorporated into the PMMA matrix

The dielectric properties of tetraethylammonium dibromo-dichloro-cobaltate (N(C₂H₅)₄)₂CoCl₂Br₂ (TEA-CBC) nanocrystallites incorporated into the polymethylmethacrylate (PMMA) matrix were investigated within the spectral range of 3 × 10⁵–3 × 10⁹ Hz in the temperature range of 90–300 K. The considerable difference of the dielectric spectra of the nanocomposite compared to the TEA-CBC crystal and to the pure PMMA matrix was observed. The phenomenon of the ‘negative capacity’ has been found in the considered material. Its dependence on the NC content was investigated. Temperature investigations of the dielectric permittivity for the TEA-CBC NC incorporated into the polymer PMMA matrices have shown the sharp-like resonance dependences of the imaginary part of the dielectric permittivity near 1.2 GHz. The intensity of the corresponding resonance peaks increase sub-linearly with increasing NC content. Taking into account the substantial growth of the imaginary part of the permittivity with increasing NC concentration, one can assume that the main contribution to the effect is given by the interface NC-PMMA regions. Additional experiments were performed to eliminate the influence of ‘geometry factor’.     

On the Dielectric Behavior of Unaligned Samples of 4-n-Octyl-4′-cyanobiphenyl (8CB)

Data on the dielectric properties of the liquid crystal 4-octyl-4′-cyanobiphenyl (8CB) have been determined onto unaligned samples, for a large scale of frequency, as function of temperature. The components of the complex dielectric permittivity as well as the corresponding dielectric parameters were evaluated using Havriliak-Negami (HN) functions. The dielectric characteristics were discussed and were compared with the literature, a good agreement being observed. The method allows to obtain for the first time the dielectric strength for a large range of the temperature and gives the two functions describing the relaxation processes in the isotropic range.     

大尺寸氟化钡晶体的生长

通过软件模拟设计合理的炉体温场结构,并对晶体原料的提纯及生长工艺条件进行优化,采用改进的坩埚下降法成功地制备出了大尺寸、高质量的氟化钡晶体.晶体的透过率在0.2 ～10 μm波长范围内高于85;,最高透过率约为94;.