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1.
利用原位高压拉曼散射和X射线衍射技术,研究了KBrO3在高压下晶格振动和晶体结构演化行为.最高压力达30.9 GPa.通过拉曼光谱发现,在高压下拉曼峰位除了单调移动,没有其它变化,表明KBrO3在研究的压力范围没有发生相变.原位高压X射线衍射实验数据显示,其在高压下依然保持常压的六方结构.通过进一步分析,分别得到了体弹模量B0=25.9(2) GPa(B′0=5.68(0.38))和部分拉曼峰的Grüneisen参数.  相似文献   

2.
异多核金属三键(W≡C)有机化合物的红外和拉曼光谱研究   总被引:1,自引:0,他引:1  
五种 (Ⅰ ,Ⅱ ,Ⅲ ,Ⅳ ,Ⅴ )异多核金属钨三键W≡C金属有机化合物的红外和拉曼光谱研究表明 ,由于N和P原子为强的σ 给予体和弱的π 接受体 ,在金属原子上分别引入含N或P的功能基团 (TMEDA或DPPE)将降低金属三键 (W≡C)的键强度 ,W≡C伸缩振动νW≡C 波数下降。化合物Ⅲ的压力调制红外和拉曼光谱显示 ,在 2 0kbar压力附近存在一压力诱导相变。低压相区高的压力灵敏度dv/dp(0 75cm-1·kbar-1)和高压相区很低的压力灵敏度 (0 0 8cm-1·kbar-1)指出 ,对W≡C键存在两种压力效应 ,一种是正常的 ,W≡C键强度随压力增加而增强 ,伸缩振动 νW≡C 波数增加 ;另一种是随着压力增加 ,从W到COπ 轨道反馈增加 ,导致W≡C键强度减弱 ,伸缩振动νW≡C 波数下降。  相似文献   

3.
本文利用高斯 94从头计算程序在 6- 31 G基组下对二甲基硅硼烷 ,o- (Si Me) 2 B1 0 H1 0 ,进行几何优化及振动光谱的理论计算 ,并对主要谱带特性进行指认 ,结果与实验基本符合。振动模式分析表明 450 cm-1 以下的两个强带中 32 6cm-1 (计算值为 369cm-1 )似乎是两个 Si原子相对笼骨架中其余 B原子整体的伸缩振动 ,而 399cm-1 (计算值为 42 1 cm-1 )则为 Si- Si(及其联带的 C原子一起参与的 )对称伸缩振动。优化几何及振动光谱的研究表明重的杂原子硅占据二十面体硼笼骨架位置后使笼结构的刚性弱化  相似文献   

4.
根据空间群理论分析和指认了磷酸二氘钾晶体[K(DxH1-x)2PO4,简称DKDP]的拉曼活性晶格振动模,测量了其室温拉曼光谱.结果表明DKDP晶体的晶格振动谱主要是由D2PO4-阴离子团簇的内振动引起的.与HzPO4-阴离子稀溶液的拉曼谱和NaD2(PO4)2晶体的拉曼谱比较,DKDP晶体中D2PO4-阴离子的四个特征内振动模可被指认为881 cm-1(v1),357 cm-1(v2),514/541 cm-1(v3),965 cm-1(v4).  相似文献   

5.
用空间群理论分析和指认了KDP晶体的拉曼活性晶格振动模 ,测量了晶体以及生长溶液的拉曼光谱 ,重点分析了出现在固 /液界面附近的 91 6cm- 1拉曼峰 ,该峰被指认为扭曲的P(OH) 2 集团反对称伸缩振动。依据本文的理论分析和实验测量 ,我们认为H2 PO- 4阴离子集团的二聚物可能是KDP晶体的生长基元。  相似文献   

6.
本文主要通过高压拉曼光谱研究了正铁氧体SmFeO3的晶格振动模式在外加压力作用下的行为规律,高压实验中压力最高为29.7GPa。本文采用溶胶凝胶法,制备出具有正交结构,其空间群为Pnma的SmFeO3。在外加压力作用下,所有观察到的拉曼振动模式都呈现出宽化趋势。特别是位于621.1cm-1的FeO6八面体的反弹性振动模式Ag(1)与位于452.7cm-1的FeO6八面体的弯曲振动模式B3g(3),其压力系数出现最大值。与此相反,Sm-O振动模式Ag(7)的压力系数却非常小。这说明外加压力更容易影响到FeO6八面体的晶格变化,而不是SmO12十七面体的改变。SmFeO3的这种高压下晶格振动模式变化行为类似于G型结构的CaSnO3。同时,文中还给出了所有声子零压模式下的格林爱森参数与体弹模量的比值。这些参数可用于进一步测量单轴或者双轴的应变力,可深入理解声子频率在张力作用下移动的表现行为。  相似文献   

7.
利用活塞圆筒装置在1.2 GPa,1473 K的条件下合成了白硅钙石。采用外加热装置和金刚石压腔结合拉曼光谱分析技术,采集了白硅钙石298,353,463,543,663,773以及873 K温度区间的常压及1 atm~14.36 GPa(常温)压力区间的拉曼谱图。扫描电镜下,该研究合成的样品为结构一致的单一相,颗粒大小为10~20μm。电子探针分析结果表明,样品的组成为 Ca7.03(2)Mg0.98(2)Si3.94(2)O16,该组分完全吻合白硅钙石理论组分。Raman分析结果表明,高温时白硅钙石的拉曼谱图中具有29个振动峰。随着温度的升高,部分振动峰出现了合并或者弱化消失的现象。该现象尤其以800~1200 cm-1范围内的909,927和950 cm-1振动峰峰位最为明显,这些振动峰分别在873,773以及873 K时弱化消失。据此,白硅钙石的结构在实验温压范围内稳定,且随着温度和压力的升高,其拉曼振动峰峰位分别呈现往低频和高频方向线性飘移的趋势。除此之外,根据高温和高压拉曼实验的结果,分别计算了白硅钙石拉曼振动峰峰位的等压 mode-Grüneisen参数和等温mode-Grüneisen参数,其算术平均值分别为1.47(2)和0.45(3)。最后结合高温和高压拉曼实验的结果,计算了白硅钙石的非谐系数,结果表明,Si-O振动模式对于非谐效应的贡献要小于其他振动模式。  相似文献   

8.
采用密度泛函的B3LYP和B3PW91方法在6-311++G**基组水平上全优化了D-荧光素分子的平衡构型和振动光谱。采用标度量子力学力场(SQM)方法研究了D-荧光素分子的振动光谱。为了详细分析振动模式的贡献,定义了分子的局域内坐标,用改编的分子振动计算程序组将计算的笛卡尔坐标力常数转换成了局域内坐标力常数。用GF矩阵方法进行了简正坐标分析,获得了振动频率和势能分布(PEDs)。根据PEDs对所有的振动模式进行了指认。结果表明,在红外光谱中,所有振动模式均有红外活性,其中吸收强度最强的峰的振动频率为1 780cm-1,吸收强度为507KM·mol-1,根据计算所得的PEDs矩阵,可以清楚的看出该振动吸收峰主要由羧基C21O22双键伸缩振动所贡献,其PEDs为93%。在拉曼光谱中,D-荧光素分子的所有振动模式也表现出了拉曼活性,振动频率在1 200~1 700cm-1范围的吸收峰具有较强的拉曼活性。其中吸收强度最强的吸收峰的频率为1 573cm-1,吸收强度为297KM·mol-1,是五元环CN键的伸缩振动所贡献。结果可为进一步研究荧光素衍生物的结构、发光活性提供一定的理论依据。  相似文献   

9.
在对Grüneisen系数高温高压下演化特性不作任何假设的前提下,建立了一种不依赖于等温物态方程具体形式,通过Hugoniot实验数据直接确定0K零压等温体积模量B0K及其对压力的一阶导数B′0K和初始密度ρ0K等0K物态方程输入参数的方法。通过与实验和理论数据的分析和比较,表明用这一方法确定的B0K和B′0K不仅合理,而且具有很高的精度,特别是B′0K的精度,要优于目前传统超声实验的测量精度。此外,这一方法所确定的ρ0K不仅在Gr櫣neisen物态方程的框架内与相应的室温零压特性参数相适配,而且与低温热膨胀实验数据所确定的近0K初始密度ρ0E非常吻合。  相似文献   

10.
刘影  郝伟  卢昊 《光散射学报》2014,26(2):144-147
对硼酸(H3BO3/B(OH)3)粉末进行XRD测试,确定其空间结构和所属对称点群;对硼酸晶体进行晶格振动模式分析,确定其有18个拉曼活性模式4Ag+2E1g+5E2g;并对其进行50~3800cm-1波段的Raman散射测试,利用理论结果对谱图进行了讨论,确定了各振动峰的特性。  相似文献   

11.
The thermal expansion against temperature of ZnS, ZnSe and ZnTe is studied theoretically using the experimental pressure dependence of elastic stiffness constants and phonon frequencies. The mode Grüneisen parameters obtained from the high pressure effect on the one- and two- phonon Raman spectra at the metallic transition pressure by Weinstein are used originally, but do not reproduce the experimental linear expansion coefficient at high temperatures. The contributions from optical modes with large phonon frequency are important to the thermal expansion at high temperatures, and a set of mode Grüneisen parameters, which bring good agreement with the observed linear expansion coefficient not only at low temperatures, but also at high temperatures, are obtained. Then, the phonon dispersion curves of ZnS, ZnSe and ZnTe at their metallic transition pressures are quantitatively shown.  相似文献   

12.
Isotropic negative thermal expansion has been reported in cubic ZrW2O8 over a wide range of temperatures (0-1050 K). Here we report the direct experimental determination of the Grüneisen parameters of phonon modes as a function of their energy, averaged over the whole Brillouin zone, by means of high pressure inelastic neutron scattering measurements. We observe a pronounced softening of the phonon spectrum at P = 1.7 kbar compared to that at ambient pressure by about 0.1-0.2 meV for phonons of energy below 8 meV. This unusual phonon softening on compression, corresponding to large negative Grüneisen parameters, is able to account for the observed large negative thermal expansion.  相似文献   

13.
The volume-dependence of phonon frequencies for Si and Ge is studied using higher-order perturbation and local Heine-Abarenkov model pseudopotential. The obtained mode Grüneisen parameters at atmospheric pressure are in good agreement with the experimental data. The mode Grüneisen parameters obtained for the Raman, TO, LO and LA modes increase slightly with decreasing volume. The other TA mode Grüneisen parameters decrease strongly as function of the volume strain, and give important contribution to the anharmonic properties of Si and Ge. The pressure dependence of phonon frequencies for Raman and some modes at the zone boundaries are estimated over the whole region of the compressed volume before the pressure induced covalent-metallic phase transition.  相似文献   

14.
The thermal expansion of GaP is estimated theoretically as a function of temperature using the experimental pressure dependence of elastic stiffness constants and phonon frequencies. The numerical values of the linear expansion coefficient and the Grüneisen constant do not become negative at low temperatures, contrary to other tetrahedrally bonded covalent solids. This positive thermal expansion of GaP at low temperatures is closely connected with the small values of the transverse acoustical mode Grüneisen parameter and with the large value of the metallic phase transition pressure from the linear correlation obtained by Weinstein.  相似文献   

15.
An infrared study of the phonon spectra of ZrW2O8 as a function of temperature which includes the low-energy (2-10 meV) region relevant to negative thermal expansion is reported and discussed in the context of specific heat and neutron density of state results. The prevalence of infrared active phonons at low energy and their observed temperature dependence are highly unusual and indicative of exotic low-energy lattice dynamics. Eigenvector calculations indicate a mixing of librational and translational motion within each low-frequency IR mode. The role of the underconstrained structure in establishing the nature of these modes and the relationship between the IR spectra and the large negative thermal expansion in ZrW2O8 are discussed.  相似文献   

16.
Yaguang Hao 《中国物理 B》2022,31(4):46502-046502
We report a new type of near-zero thermal expansion material β-CuZnV2O7 in a large temperature range from 173 K to 673 K. It belongs to a monoclinic structure (C2/c space group) in the whole temperature range. No structural phase transition is observed at atmospheric pressure based on the x-ray diffraction and Raman experiment. The high-pressure Raman experiment demonstrates that two structural phase transitions exist at 0.94 GPa and 6.53 GPa, respectively. The mechanism of negative thermal expansion in β-CuZnV2O7 is interpreted by the variations of the angles between atoms intuitively and the phonon anharmonicity intrinsically resorting to the negative Grüneisen parameter.  相似文献   

17.
The third order contribution of the shell-shell interaction between next nearest neighbours has been determined from a calculation of the coefficient of linear thermal expansion of LiH and 7LiD. The Coulomb anharmonicity is included. A shell model fitted to phonon energies from inelastic neutron scattering in 7LiD was used. From this model then averaged Grüneisen constants and individual mode Grüneisen parameters have been deduced.  相似文献   

18.
Using the local-density approximation, calculating the Hellmann-Feynman forces and applying the direct method, the phonon dispersion relations for the rutile-like structure of crystalline SnO2 have been derived for the first time. The phonon frequencies at the point agree very well with Raman and infrared data and other phenomenological model calculations. The LO/TO splitting is estimated by calculating phonons from an elongated supercell. The computations under pressure reveal a soft mode of B1g symmetry which leads to a ferroelastic phase transition. The pressure-dependence of the lattice constants and the Grüneisen parameters of the modes are calculated. Received 18 July 1999  相似文献   

19.
R K Soni  K P Jain 《Pramana》1986,27(5):707-712
The pressure dependence of various phonon modes has been investigated through the ferro-paraelectric phase transition. Most mode frequencies harden before levelling off above the phase transition. Mode Grüneisen parameters are estimated from the pressure dependence of phonon frequencies.  相似文献   

20.
Abstract

Employing resonant Raman and luminescence spectroscopy, various exciton states and phonon modes are studied at low temperature in AgBr under hydrostatic pressure up to 0.7 GPa. The deformation potential for the indirect free exciton gap and mode Grüneisen parameters for various phonons are determined. Excitons bound to neutral donors and isoelectronic iodine are found to essentially derive from L-point valence band states.  相似文献   

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