高压下铌酸锌钶铁矿结构相变的原位拉曼光谱和X射线衍射研究

通过原位高压拉曼光谱和X射线衍射对ZnNb₂O₆晶体在29 GPa以下的结构转变进行了研究.拉曼光谱显示, 多数拉曼峰强度减弱, 且随着压力增加向高波数方向移动.压力频移曲线分别在10, 16 和20 GPa处形成了拐点.原位X射线衍射谱在10.6 GPa以上有旧峰消失和新峰出现.结果分析表明, ZnNb₂O₆钶铁矿结构压缩过程中发生了一个可逆压致相变, 此相变从10 GPa左右开始, 到16 GPa左右完成, 继续增加压力到20 GPa以上则形成无序状态.     

8-羟基喹啉及其衍生物的锌配合物合成研究进展

简述了有机发光材料8-羟基喹啉金属螯合物的发展,综述了固相法和液相法合成8-羟基喹啉锌,例举了在喹啉环上的2、5和7号位引入供电子基团或大共轭基团的8-羟基喹啉衍生物的锌配合物性质,介绍了通过改变聚合度制备8-羟基喹啉衍生物的锌配合物方法,杂环和8-羟基喹啉共同做锌的配体合成新的发光材料的方法;最后对8-羟基喹啉和8-羟基喹啉衍生物的锌配合物的合成进行总结和展望。     

高压下D,L-扁桃酸结构相变的拉曼光谱研究

采用金刚石对顶砧高压装置,在室温下对D,L-扁桃酸(C8H8O3)进行了原位高压拉曼光谱研究,实验最高压力为2.2 GPa.结果表明,原来的一些拉曼峰在0.6 GPa左右突然消失或者劈裂,并同时出现了一些新的拉曼峰.通过进一步分析D,L-扁桃酸的拉曼频率随压力的变化,发现许多拉曼峰的移动在0.6 GPa时都出现了拐点.D,L-扁桃酸在0.6 GPa发生了由正交相(Pbca)到单斜相(P21/c)的压致结构相变.通过分析相变前后晶体结构及拉曼振动模式的变化,认为此压致结构相变是由高压下分子的密堆积效应和氢键结构的重新排列导致.完全卸压至常压后,卸压拉曼光谱与常压拉曼光谱一致,表明此压致相变可逆.     

金刚石Raman光谱荧光本底及其对高压原位Raman光谱测试的影响

金刚石对顶砧(diamond anvil cell,DAC)装置(如图1所示)是目前产生压力最高的静态高压实验装置,它以金刚石单晶作对顶砧单轴挤压样品产生高压,由于金刚石在很宽的能量范围对光子(可见光、高能X射线等)透明,在高压实验中可以通过显微镜观察样品,并可对样品进行高压原位X射线衍射和光谱(红外光谱、Raman光谱等)测试,这一特点使其在高压科学领域得到广泛的应用.在高压原位Raman光谱测试中,激发光源透过金刚石对顶砧照射到样品上产生Raman信号,样品的Raman信号穿过金刚石对顶砧经显微镜物镜收集并最终被探测器接收.与常规的Raman光谱测试相比,基于DAC装置的高压原位Raman光谱测试光路中多出了金刚石对顶砧,需要采用长焦物镜收集信号,并且随着实验压力的升高,样品的Raman信号强度降低,因此提高信噪比是获得较高质量高压原位Raman光谱的关键,而金刚石对顶砧的荧光本底是影响信噪比的关键因素.本文通过对20多颗金刚石对顶砧进行Raman光谱测试,对金刚石的Raman光谱信号(一级和二级)和非随机噪声进行了系统的评估,并结合高压原位Raman光谱测试的具体特点,探讨金刚石对顶砧荧光本底对测试结果的影响.     

8-羟基喹啉席夫碱衍生物及其金属配合物的合成及荧光性质研究

设计合成了三种新的8-羟基喹啉席夫碱衍生物4-(8-羟基喹啉-5-亚胺甲基)-7-甲氧基苯并吡喃-2-酮(3a),4-(8-羟基喹啉-5-亚胺甲基)-7-己氧基苯并吡喃-2-酮(3b)和4-(8-羟基喹啉-5-亚胺甲基)-7-十八烷氧基苯并吡喃-2-酮(3c)及其铝、锌配合物,产物结构经1H(13C)NMR,MS,HRMS,IR和元素分析表征,研究了它们的荧光发光性能.     

微纳米VO2膜层高温相变原位X射线衍射测试方法研究

通过设计、自制加热样品台结合商业X射线衍射仪的小角掠入射衍射模式,开发了微纳米膜层的原位高温相变测试方法,解决了样品表面微纳米膜层材料（厚度 < 10 μm）的高温相变难以原位测量的问题.研究了样品台与膜层表面的温度分布特征,验证了自制加热样品台的控温效果,原位测试了不同温度下二氧化钒（VO₂）膜层的X射线衍射图谱,揭示了VO₂膜层的高温相变行为.     

YBa2Cu3O7—x超导化合物在加热过程中相转变的高压电镜原位观察

对YBa_2Cu_3O_(7-x)超导化合物在加热过程中的相转变进行了高压电镜原位观察,并做了在空气中的X射线衍射分析和真空处理样品的X射线衍射物相分析。结果表明,在真空环境下,相变温度与氧含量有关,一般比在空气中低100～120℃。在320～350℃,孪晶带开始消失,在样品表面出现一些Cu_2O黑斑,并开始由正交结构YBa_2Cu_3O_(7-x)向正交结构Y_2BaCuO_5化合物转变,在500℃左右相转变结束。在冷却过程中未发现相转变。     

硝基苯2位取代8-羟基喹啉锌配合物的合成及光学性质研究

近年来许多研究表明8-羟基喹啉是一个良好的发光性材料,在8-羟基喹啉环上引入不同的功能团可以调控其相应锌配合物的发光颜色。本文在2位上引入硝基苯基团,设计合成了2-(4-硝基苯-乙烯基)-8-羟基喹啉(1)和2-(3-硝基苯-乙烯基)-8-羟基喹啉(2)及其各自的锌配合物(3)、(4)四个新化合物;利用UV、荧光等分析其结构及研究其反应;紫外光谱显示化合物3和4的λmax分别是340nm和305nm。     

以5-取代-8-羟基喹啉和2-苯基吡啶为配体的金属铱配合物的合成、表征及光致、电致发光性质

本文通过在8-羟基喹啉的5位上引入氨基和取代的苯基,合成了系列二-[2-苯基吡啶（C^N）][5-取代-8-羟基喹啉（N^O）]铱（Ⅲ）配合物（（C^N）2IrQ）.这里CN代表2-苯基吡啶,Q代表5-取代-8-羟基喹啉.通过1HNMR、13CNMR、MS、元素分析、单晶X-衍射等对配合物的化学和晶体结构进行了表征.利用循环伏安、UV-Vis、光致和电致发光光谱等对它们的光物理性质进行了表征.热重分析表明苯环上的取代基对配合物热稳定性有很大影响.常温下,几种5-取代苯基喹啉铱配合物的溶液和固体产生红色磷光发射,光致发光（PL）光谱在666和687nm附近出现两个强度基本相等的发射峰.配合物的发光性质主要受喹啉环和5位苯基的影响,苯环上的取代基团对配合物的发光性质影响不大.而5-氨基喹啉铱配合物PL光谱的最大发射峰在550nm,其PL光谱主要受2-苯基吡啶的影响.将配合物二-[2-苯基吡啶（C^N）][5-（4-甲氧基苯基）-8-羟基喹啉（N^O）]铱（Ⅲ）（7b）掺杂在聚2,7-（9,9-二辛基）芴（PFO）和30%（质量分数）的2-对叔丁基苯基-5-对联苯基-1,3,4-口恶二唑（PBD）的主体材料中,制备了聚合物发光器件（OLED）,器件电致发光（EL）光谱的发射峰在672nm处,18V时最大亮度为350cd/m2,在电压14V时CIE色坐标值为（0.61,0.33）,是一红光OLED器件.     

掺杂钙铬酸镧材料的低温相变行为

通过DSC, X射线衍射等技术研究了一系列掺杂钙铬酸镧材料的低温相变行为, 并对其热膨胀过程进行了分析. 发现铬酸镧在240 ℃左右发生低温相变, 在260 ℃左右结束. 随钙含量的增加, 相变的开始和终了温度均显著升高, 相变属吸热反应. 铬酸镧及掺杂铬酸镧材料的低温结构相变均是由正交结构向菱形结构的转变. 在相变过程中无明显质量变化, 但会发生较大的体积收缩.     

Pressure-induced structural changes of the tetragonal Bi2CuO4

The tetragonal compound Bi₂CuO₄ was investigated at high pressures by using in situ Raman scattering and X-ray diffraction (XRD) methods. A pressure-induced structural transition started at 20 GPa and completed at ∼37 GPa was found. The high pressure phase is in orthorhombic symmetry. Raman and XRD measurements revealed that the above phase transition is reversible.     

Untersuchung von CuGaSe2 und CuGaTe2 unter hohem Druck

Investigation of CuGaSe₂ and CuGaTe₂ under High Pressure The X-ray powder diffraction analysis at 300 K in dependence on the pressure gives a transition from the chalcopyrite-type to the NaCl structure for CuGaSe₂ at 12.5 GPa and for CuGaTe₂ at 8 GPa. The phase transition is associated with a discontinuity of the volume of 8.6 and 3.8%. These results were discussed in relation to other tetrahedrally coordinated compounds.     

Perovskite-to-postperovskite transitions in NaNiF3 and NaCoF3 and disproportionation of NaCoF3 postperovskite under high pressure and high temperature

High-pressure structural phase transitions in NaNiF(3) and NaCoF(3) were investigated by conducting in situ synchrotron powder X-ray diffraction experiments using a diamond anvil cell. The perovskite phases (GdFeO(3) type) started to transform into postperovskite phases (CaIrO(3) type) at about 11-14 GPa, even at room temperature. The transition pressure is much lower than those of oxide perovskites. The anisotropic compression behavior led to heavily tilted octahedra that triggered the transition. Unlike oxide postperovskites, fluoropostperovskites remained after decompression to 1 atm. The postperovskite phase in NaCoF(3) broke down into a mixture of unknown phases after laser heating above 26 GPa, and the phases changed into amorphous ones when the pressure was released. High-pressure and high-temperature experiments using a multianvil apparatus were also conducted to elucidate the phase relations in NaCoF(3). Elemental analysis of the recovered amorphous samples indicated that the NaCoF(3) postperovskite disproportionated into two phases. This kind of disproportionation was not evident in NaNiF(3) even after laser heating at 54 GPa. In contrast to the single postpostperovskite phase reported in NaMgF(3), such a postpostperovskite phase was not found in the present compounds.     

New observations on the pressure dependence of luminescence from Eu2+-doped MF2 (M = Ca, Sr, Ba) fluorides

The luminescence from Eu(2+) ions in MF2 (M = Ca, Sr, Ba) fluorides has been investigated under the pressure range of 0-8 GPa. The emission band originating from the 4f(6)5d(1) --> 4f(7) transition of Eu(2+) ions in CaF2 and SrF2 shows the red-shift as increasing pressure with pressure coefficients of -17 meV/GPa for CaF2 and -18 meV/GPa for SrF2. At atmospheric pressure, the emission spectrum of BaF2:Eu(2+) comprises two peaks at 2.20 and 2.75 eV from the impurity trapped exciton (ITE) and the self-trapped exciton (STE), respectively. As the pressure is increased, both emission peaks shift to higher energies, and the shifting rate is slowed by the phase transition from the cubic to orthorhombic phase at 4 GPa. Due to the phase transition at 4-5 GPa pressure, the ITE emission disappears gradually, and the STE emission is gradually replaced by the 4f(6)5d(1) --> 4f(7) transition of Eu(2+). Above 5 GPa, the pressure behavior of the 4f(6)5d(1) --> 4f(7) transition of Eu(2+) in BaF2:Eu(2+) is the same as the normal emission of Eu(2+) in CaF2 and SrF2 phosphors.     

Supramolecular reaction between pressure-frozen acetonitrile phases alpha and beta

The balance of weak CH...N bonds involving the H 3C- and -CN groups has been related to the structural rearrangement between centrosymmetric and polar acetonitrile structures. The linear highly polar molecules arrange antiparallel in phase alpha below a freezing temperature of 225 K/0.1 MPa and above a freezing pressure of 0.38(5) GPa/296 K and in a polar mode in phase beta below 206 K/0.1 MPa and at pressures higher than 0.63(5) GPa/296 K. The alpha <--> beta phase transition has been considered as a supramolecular reaction between 2-dimensional and 3-dimensional hydrogen-bonding networks, the latter favoring the polar association. Acetonitrile has been in situ pressure-frozen, and its structure has been determined at room temperature by single-crystal X-ray diffraction at 0.57(5), 0.63(5), and 1.50(5)GPa. The crystallization pressure at 296 K has been determined as 0.38(5) GPa both by ruby fluorescence in a diamond anvil-cell and by the compressibility measurement in a cylinder-and-piston device. Acetonitrile mixed with methanol trimerized at 1.60 GPa and 473 K yielding 4-amino-2,6-dimethylpyrimidine: it was in situ crystallized, and the structure of a single crystal, recovered at ambient conditions, was determined.     

Pressure-induced cubic to monoclinic phase transformation in erbium sesquioxide Er(2)O(3)

Cubic Er(2)O(3) was compressed in a symmetric diamond anvil cell at room temperature and studied in situ using energy-dispersive X-ray diffraction. A transition to a monoclinic phase began at 9.9 GPa and was complete at 16.3 GPa and was accompanied by a approximately 9% volume decrease. The monoclinic phase was stable up to at least 30 GPa and could be quenched to ambient conditions. The normalized lattice parameter compression data for both phases were fit to linear equations, and the volume compression data were fit to third-order Birch-Murnaghan equations of state. The zero-pressure isothermal bulk moduli (B(0)) and the first-pressure derivatives (B(0)') for the cubic and monoclinic phases were 200(6) GPa and 8.4 and also 202(2) GPa and 1.0, respectively. Ab initio density functional theory calculations were performed to determine optimized lattice parameters and atom positions for the cubic, monoclinic, and hexagonal phases of Er(2)O(3). The calculated X-ray spectra and predicted transition pressure are in good qualitative agreement with the experimental results.     

Compression behaviors of binary skutterudite CoP3 in noble gases up to 40 GPa at room temperature

The binary skutterudite CoP(3) has a large void at the body-centered site of each cubic unit cell and is, therefore, called a nonfilled skutterudite. We investigated its room-temperature compression behavior up to 40.4 GPa in helium and argon using a diamond-anvil cell. High-pressure in situ X-ray diffraction and Raman scattering measurements found no phase transition and a stable cubic structure up to the maximum pressure in both media. A fitting of the present pressure-volume data to the third-order Birch-Murnaghan equation of state yields a zero-pressure bulk modulus K(0) of 147(3) GPa [pressure derivative K(0)' of 4.4(2)] and 171(5) GPa [where K(0)' = 4.2(4)] in helium and argon, respectively. The Gru?neisen parameter was determined to be 1.4 from the Raman scattering measurements. Thus, CoP(3) is stiffer than other binary skutterudites and could therefore be used as a host cage to accommodate large atoms under high pressure without structural collapse.     

In situ high-pressure x-ray diffraction study of H2O ice VII

Ice VII was examined over the entire range of its pressure stability by a suite of x-ray diffraction techniques in order to understand a number of unexplained characteristics of its high-pressure behavior. Axial and radial polycrystalline (diamond anvil cell) x-ray diffraction measurements reveal a splitting of diffraction lines accompanied by changes in sample texture and elastic anisotropy. In situ laser heating of polycrystalline samples resulted in the sharpening of diffraction peaks due to release of nonhydrostatic stresses but did not remove the splitting. Radial diffraction measurements indicate changes in strength of the material at this pressure. Taken together, these observations provide evidence for a transition in ice VII near 14 GPa involving changes in the character of the proton order/disorder. The results are consistent with previous reports of changes in phase boundaries and equation of state at this pressure. The transition can be interpreted as ferroelastic with the appearance of spontaneous strain that vanishes at the hydrogen bond symmetrization transition near 60 GPa.     

Pressure-induced isostructural phase transition and correlation of FeAs coordination with the superconducting properties of 111-type Na(1-x)FeAs

The effect of pressure on the crystalline structure and superconducting transition temperature (T(c)) of the 111-type Na(1-x)FeAs system using in situ high-pressure synchrotron X-ray powder diffraction and diamond anvil cell techniques is studied. A pressure-induced tetragonal to tetragonal isostructural phase transition was found. The systematic evolution of the FeAs(4) tetrahedron as a function of pressure based on Rietveld refinements on the powder X-ray diffraction patterns was obtained. The nonmonotonic T(c)(P) behavior of Na(1-x)FeAs is found to correlate with the anomalies of the distance between the anion (As) and the iron layer as well as the bond angle of As-Fe-As for the two tetragonal phases. This behavior provides the key structural information in understanding the origin of the pressure dependence of T(c) for 111-type iron pnictide superconductors. A pressure-induced structural phase transition is also observed at 20 GPa.