LiB3O5晶体高温拉曼光谱研究

研究了LiB3 O5晶体在不同温度下(在300-1173 K的温度范围)的拉曼光谱,分析了LBO晶体结构随温度变化的规律.随着温度的升高,LBO晶体的拉曼光谱谱峰都不同程度地向低波数方向移动,也存在不同程度的展宽,同时强度减弱.发现晶体在1100 K存在明显相变,与LBO晶体的相图给出的1107 K的相变温度基本相符.     

Li2B4O7晶体及其熔体结构的拉曼光谱研究

采用高温原位拉曼光谱技术,研究了Li₂B₄O₇从常温至1 373 K温度范围内的拉曼光谱。在升温过程中,晶体的拉曼光谱出现展宽和红移现象,且强度降低。晶体熔化时,由2个[BO₄]和2个[BO₃]组成的[B₄O₉]环状结构转变成(B₃O₆)3- 六元环和[BO₃]结构,[BO₄]结构减少直至消失。基于密度泛函理论,计算了Li₂B₄O₇晶体的拉曼光谱,对其振动模式进行了分析归属。利用量子化学从头计算法计算了由[B₃O₆-BO₃]为基础相互连接形成的x(Li₂B₄O₇)(x=2, 3, …, 9)的环状团簇模型的拉曼光谱,对Li₂B₄O₇熔体的结构进行了模拟分析。计算结果表明Li₂B₄O₇熔体的阴离子基元为三个(B₃O₆-BO₃)组成的大三元环超级结构。     

Bi4Ge3O12晶体及其熔体结构的高温拉曼光谱研究

研究了BGO晶体在不同温度下(在300—1323 K的温度范围)的拉曼光谱及其熔体的高温拉曼光谱，分析了BGO晶体结构随温度变化的规律及BGO熔体的结构特征.随着温度的升高，BGO晶体的拉曼光谱谱峰都不同程度地向低波数方向移动，也存在不同程度的展宽，同时强度减弱.另外，在BGO熔体中存在［GeO₄］和［BiO₆］的结构基团；但两种结构之间的联键消失，即在熔体中二者是相互独立的生长基元. 关键词： 高温拉曼光谱 熔体 BGO晶体     

Bi2ZnOB2O6单晶偏振拉曼光谱

本文通过分析不同几何配置下的偏振拉曼光谱对非线性光学晶体的晶格振动模式进行了研究. 首先根据因子群分析,将晶体的振动模按晶体对称群的不可约表示进行分类,其次测量了晶体在10–1600 cm^-1范围内,不同几何配置下的偏振拉曼光谱,并在此基础上指认了晶体的晶格振动模式. 300 cm^-1以下的振动峰,归结为晶体的外振动,来自[BiO₆],[ZnO₄],[BO₄]和[BO₃]原子基团的平动和转动;300cm^-1以上为晶体的内振动,主要与Bi-O,和Zn-O键振动有关. 晶体拉曼光谱中最高振动频率达到1407 cm^-1,被指认为[BO₃]三角形中B-O键的伸缩振动,体现了[BO₃]基团中高的电子非局域化程度. 关键词： 2ZnOB₂O₆单晶')" href="#">Bi₂ZnOB₂O₆单晶 偏振拉曼光谱 振动模式     

正磷酸盐晶体Ba3(PO4)2和Sr3(PO4)2高温拉曼光谱研究

测量了碱土金属正磷酸盐Ba₃(PO₄)₂和Sr₃(PO₄)₂常温及高温拉曼光谱, 对拉曼振动模式进行指认, 并分析了晶体拉曼振动光谱及晶体结构在高温下的变化. 在温度升高的过程中, 拉曼振动频率向低频移动且振动峰宽度展宽, 晶体中的P-O平均键长随温度升高而变长, 但O-P-O的键角并未发生变化. 晶体在900 ℃以下无结构相变发生. 关键词： 3(PO₄)₂和Sr₃(PO₄)₂')" href="#">Ba₃(PO₄)₂和Sr₃(PO₄)₂ 高温拉曼光谱 振动模式 高温结构     

碱金属阳离子对[B3O7]型非线性光学晶体结晶习性的影响

本文利用高温拉曼光谱技术和从头计算的方法, 研究了LiB₃O₅和CsB₃O₅晶体高温熔融体的结构, 分析了碱金属阳离子对熔体结构的影响, 以及熔体结构的差异与LiB₃O₅和CsB₃O₅晶体结晶习性的联系. 结果表明: LiB₃O₅和CsB₃O₅晶体高温熔融体中的结构基团 主要为B₃Ø₇和B₃Ø₆两种不同类型的硼氧六元环; 环内BØ₄ 四面体的数量影响了六元环呼吸振动峰的拉曼频率, 随BØ₄四面体数量的增加六元环呼吸振动峰向低频移动; LiB₃O₅晶体高温熔融体中, BØ₄四面体含量相对较多; 然而, 离子半径相对较大的Cs⁺离子却阻碍了熔体中BØ₄四面体的形成, 造成CsB₃O₅晶体高温熔融体中BØ₄/BØ₃比值的降低. 结合LiB₃O₅和CsB₃O₅晶体生长动力学过程的分析 (Wang D, Wan S M et al. 2011 Cryst. Eng. Comm. 13 5239), 阳离子的不同导致高温熔体中BØ₄四面体数量的差异, 被认为是影响LiB₃O₅和CsB₃O₅晶体结晶习性的重要因素, 有效降低高温熔体中BØ₄四面体的数量, 将是实现LiB₃O₅晶体生长的关键条件. 关键词： 硼酸盐晶体 熔体结构 拉曼光谱 结晶习性     

Dy3Al5O12磁热性质研究

用量子理论计算了Dy₃Al₅O₁₂的晶场能谱、Zeeman劈裂能级和波函数. 在外磁场H_e为0<H_e<9 T, 温度为3<T<42 K 范围内, 计算了该晶体的磁矩、磁熵变, 计算结果与相关实验数据吻合较好. 该计算结果表明, Dy₃Al₅O₁₂内磁性离子间的交换作用非常微弱, 可以忽略. 从理论上给出了绝热退磁过程中温度变化ΔT与T的关系, 并与Gd₃Ga₅O₁₂晶体进行了比较, 发现不同外磁场下, Dy₃Al₅O₁₂和Gd₃Ga₅O₁₂的低温制冷性能在不同温区有差别. 在进行低温(T<10 K)制冷时, 若外磁场较低, 选择Dy₃Al₅O₁₂作为磁制冷材料较好; 若外磁场较高, 选择Gd₃Ga₅O₁₂作为磁制冷材料较好.     

DyP5O14晶体的新相

本文首次观察到具有单斜I(P2₁/c)的DyP₅O₁₄晶体,并用光学显微镜,X射线结构分析和红外光谱等方法予以证明。DyP₅O₁₄在室温下存在着mmmF₂/m类铁弹体的单斜I结构,其铁弹相变温度为159±3℃。单斜I的DyP₅O₁₄的晶胞参数,a=8.62?,b=8.84?,c=12.82?,β=90.28°。这一发现是L _关键词：     

PbMoO4晶体生长基元和生长习性的高温拉曼光谱研究

应用高温拉曼光谱研究了PbMoO₄熔体中的生长基元.通过对不同温度下PbMoO₄晶体拉曼光谱和熔点温度附近熔体高温拉曼光谱的研究,发现PbMoO₄熔体中存在Pb²⁺阳离子和［MoO₄］^2－阴离子生长基元.进一步讨论了PbMoO₄晶体生长基元和各个低指数晶面间的相互作用,解释了晶体的生长习性和枝晶生长的原因,并指出:PbMoO₄晶体生 关键词： 钼酸铅晶体 枝晶 籽晶取向 拉曼光谱     

Bi2Sr2CaCu2O8单晶中的反常尖锋效应

使用牛津震动样品磁强计(VSM)研究了Bi₂Sr₂CaCu₂O₈单晶的磁滞回线.在20到40K温度之间发现了反常的尖锋效应,随样品O含量的增加,发生尖锋效应的外场也相应提高.可以认为在尖峰效应处发生了由涡漩物质的有序固态到无序固态的相变,在有少量点缺陷存在的BSCCO单晶相图上,B_sp线终止于20K温度处,在20K以下温区没有发生准格子到涡漩玻璃的相变,涡漩固相始终以准格子形式存在;可以认为尖峰效 关键词： 2Sr₂CaCu₂O₈单晶')" href="#">Bi₂Sr₂CaCu₂O₈单晶 磁滞回线 尖锋效应 相变     

In situ AFM and Raman spectroscopy study of the crystallization behavior of Ge2Sb2Te5 films at different temperature

Using in situ atomic force microscope (AFM) and Raman spectroscopy, the real-time crystallization properties of Ge₂Sb₂Te₅ films at different temperature were characterized. The given AFM topograph and phase images revealed that the structure of amorphous Ge₂Sb₂Te₅ films began to change at a temperature of as low as 100 °C. When the temperature reached 130 °C, some crystal fragments had formed at the film surface. Heating up to 160 °C, the size of the visible crystal fragments increased, but decreased at a higher temperature of 200 °C. When the Ge₂Sb₂Te₅ film was cooled down to room temperature (RT) from 200 °C, the crystal fragments divided into crystal grains due to the absence of heating energy. The Raman spectra at different temperature further verified the structure evolution of the Ge₂Sb₂Te₅ film with temperature. This work is of significance for the preparation of Ge₂Sb₂Te₅ films and the erasing of data.     

镶嵌在SiO2薄膜中InAs纳米颗粒的Raman散射

对镶嵌在SiO₂薄膜中纳米InAs颗粒的Raman散射谱进行了研究.与大块InAs晶体相比,InAs纳米颗粒的Raman散射谱具有相似的特征,即由纵光学声子模和横光学声子模组成,但是散射峰宽化并红移.用声子限域效应解释了散射峰的红移现象,并结合InAs纳米颗粒的应力效应解释了红移量与理论值的差异. 关键词： 2薄膜')" href="#">SiO₂薄膜 InAs量子点 Raman散射     

Investigation of the Cr:LiSrAlF6 crystal by high-temperature Raman spectroscopy

In this paper, Cr-doped LiSrAlF₆ crystals are investigated using high-temperature Raman spectroscopy and the single-crystal Raman spectra of Cr:LiSrAlF₆ are analysed by factor group theory and comparison with other fluorides. The results indicate that Cr:LiSrAlF₆ is stable below its melting point; Raman peaks located at 561, 322 and 250 cm^-1 are assigned to the A_1g modes of AlF₆, SrF₆ and LiF₆ octachdra, respectively; with temperature increasing, Raman peaks associated with AlF₆ octahedra shift towards low frequencies, while LiF₆ and SrF₆ octahedra are temperature-insensitive; around the crystal melting point, three new Raman peaks occur, which are associated with the AlF₆ octahedral chain structure. Finally, the microstructural evolution of Cr:LiSrAlF₆ from room temperature to its melting point is discussed based on its Raman spectra.     

Cd0.96Zn0.04Te低温Raman光谱中荧光背景的猝灭现象

研究了Cd_0.96Zn_0.04Te表面低温Raman散射光谱中的样品荧光背景随激光功率的变化行为,观察到了荧光的“猝灭”现象和同时伴随的声子峰红移.分析表明样品荧光的“猝灭”现象与声子峰红移显示的表面结构变化有关,而激光对Cd_0.96Zn_0.04Te表面的加热是导致表面晶体结构变化的原因. 关键词： 低温Raman光谱 0.96Zn_0.04Te')" href="#">Cd_0.96Zn_0.04Te 荧光背景 猝灭     

六方晶型MgTiO3温致微结构变化及其原位拉曼光谱研究

采用固相烧结法制备了六方晶型结构的MgTiO₃粉体. 经高温原位X射线衍射分析(293-1473 K)进行了表征与确认,获得了晶胞参数及其随温度的变化,测量了高温原位拉曼光谱(273-1623 K),并运用第一性原理理论计算方法对应核实了拉曼谱峰的归属. 结果表明,随着温度升高,MgTiO₃晶面间距和晶格常数增大,从而反映对于拉曼光谱较为敏感的键长和键角的变化;温致拉曼位移可以反映Ti-O,Mg-O等键长以及Ti-O-Ti,Ti-O-Mg与Mg-O-Mg等键角随温度的细微变化,相关关系则独立于温度,有效提升了原位拉曼光谱微探针诊断技术的分析能力;拉曼谱峰随温度升高而展宽,表明原子瞬间运动振幅加剧,弥散性增加,稳定性有所下降,但仍维持六方晶型. 关键词： 3')" href="#">MgTiO₃ 微结构 拉曼光谱 高温     

In situ Raman spectroscopy of phase transformation in CrOx-Y2O3 system at elevated temperatures

A CrO_x-Y₂O₃ sample was prepared by a deposition-precipitation method and phase transformation of the sample under N₂ and air atmospheres was characterized by in situ Raman spectroscopy and X-ray diffraction (XRD) techniques. It was found that when the CrO_x-Y₂O₃ sample was heated, CrO₃ transformed to YCrO₄ and then to YCrO₃ and Cr₂O₃. Also, the transformation started from the surface region of the sample and then extended to the bulk, due to the fact that the phase transformation was detected by Raman spectroscopy at lower temperature compared to that by XRD. In addition, both atmosphere and temperature had influence on the phase transformation in the surface region, while the phase transformation in the bulk was merely dependent on the temperature. It was also found that low oxidation state Cr(III) species on the surface could be re-oxidized to high oxidation state Cr(V) or Cr(VI) species when the thermal treated sample was exposed to ambient air.     

Effect of grain size on the magnetic properties of superparamagnetic Ni0.5Zn0.5Fe2O4 nanoparticles by co-precipitation process

Ni_0.5Zn_0.5Fe₂O₄ (NZFO) spinel-type nanoparticles were directly fabricated by the chemical co-precipitation process using metal nitrate and acetate as precursors since nitrogen and carbon would be taken away in the forms of oxynitride and oxycarbide, respectively, after the precursors were annealed and then investigated in detail by employing X-ray diffraction (XRD), magnetic measurement and Raman spectroscopy. XRD analysis indicates that the as-prepared nanocrystals are all of a pure cubic spinel structure with their sizes ranging from 20.8 to 53.3 nm, as well as peaks of some samples shifting to lower angles due to lattice expansion. Calculations from the derived XRD data indicate that the activation energy is 30.83 kJ/mol. The magnetic measurements show that these samples are superparamagnetic. The saturation magnetization increases with annealing temperature, which may be explained by super-exchange interactions of Fe ions occurring at A- and B-sites. The variation of coercivity with particle size is interpreted on the basis of domain structure and crystal anisotropy. Furthermore, these nanoparticles exhibit a redshift phenomenon at lower temperatures seen in the Raman spectra, which could be related to ionic substitution.     

K3C60在200K附近的取向相变机理

研究了K₃C₆₀单晶薄膜在200K附近的导带结构.样品温度为190K时,同步辐射角分辨光电子谱能够观察到[111]方向有规律的能带色散.而在220K附近色散不存在.这一实验结果与K₃C₆₀在200K存在取向相变相符合.用反铁磁Ising模型对实验结果进行了分析.结果表明,K₃C₆₀在200K的相变是由低温下的一维无序取向结构转变为200K以上的双取向结构畴与无序分子(约占40 关键词： 3C₆₀')" href="#">K₃C₆₀ 取向相变机理     

The Raman spectra and cross-sections of the ν2 band of H2O, D2O, and HDO

We report the experimental Raman spectra of the ν₂ band of H₂O, D₂O, and HDO in the vapor phase at room temperature. A complete interpretation of the Raman intensities is carried out employing the variational rovibrational wavefunctions obtained from a Hamiltonian in Radau coordinates and an ab initio polarizability surface at 514.5 nm. We show the importance of the rotation-vibration coupling to obtain the correct line intensities. Several tables with the assignments of the individual rotational-vibrational transitions and their Raman scattering strengths are reported. From these tables, the ν₂ Raman spectra can be simulated up to 2000 K for H₂O, and up to 300 K for D₂O and HDO.