Rb掺杂C60单晶的相衍变和电子态

在C₆₀单晶超高真空解理面上制备C₆₀的Rb填隙化合物薄膜.用同步辐射光电子能谱研究了相衍变过程.观察到对应于固溶相、Rb₁C₆₀和Rb₃C₆₀的电子态密度分布.当数纳米厚Rb₃C₆₀薄膜在C₆₀单晶（111）解理面形成后，室温条件下进一步沉积Rb至样品表面不产生fcc到bct或bcc结构相变.C_{60 关键词： 4}C₆₀和Rb₅C₆₀吸附相')" href="#">金属性Rb₄C₆₀和Rb₅C₆₀吸附相 60单晶')" href="#">C₆₀单晶 相衍变 同步辐射光电子能谱     

紫外激光和压力共同作用下C60-peapod的聚合相变研究

采用气相扩散方法将C₆₀分子填充到单壁碳纳米管(SWNTs)中，制备出高填充比率的豆荚形纳米材料C₆₀@SWNT，又称为peapod.用金刚石对顶砧(DAC)装置获得高压，在高压下同时利用紫外激光处理样品，通过激光和压力的共同作用研究了C₆₀分子在碳管内的聚合相变.在21.5GPa高压下，同时紫外激光(325nm)照射30min后，拉曼光谱表明C₆₀分子在碳管内发生了聚合，形成一维链状O相聚合结构，且该相变是不可逆的. 关键词： 60 peapod')" href="#">C₆₀ peapod 紫外激光 高压 拉曼光谱     

Lattice vibrational study of the phase transition in the plastic crystal adamantane (C10H16)

Using the Raman technique we have studied the lattice vibrations of the prototype plastic crystal adamantane (C₁₀H₁₆). The measurements, as a function of temperature through the phase transition (208K), show splittings in certain lines. At room temperature using hydrostatic pressure, we also induced a phase transition. The transition is detected by Raman measurements, and we observe splittings of the very same vibrational lines. This indicates that the pressure induced phase transition yields the same crystal structure as the low temperature structure. Some analysis of the pressure and temperature derivatives of the vibrational modes is presented.     

Phase transition at 240 K in C70 single crystal

The thermal expansion of single- and polycrystalline C₇₀ is studied between 5 and 315K using an ultrahigh-resolution capacitance dilatometer. We observe a first-order phase transition in single crystalline C₇₀ at 240K and a transition at 280K in polycrystalline C₇₀. X-ray diffraction measurements at 300K show that the C₇₀ single crystal has fcc symmetry, whereas the polycrystalline sample is multiphase (fcc and hcp). The results are compared to thermal expansion measurements of solid C₆₀.     

Elastic properties study of single crystal NH3 up to 26 GPa

Single crystal Brillouin and Raman scattering measurements on NH₃ in a diamond anvil cell have been performed under pressures up to 26 GPa at room temperature. The pressure dependencies of acoustic velocity, adiabatic elastic constants, and bulk moduli of ammonia from liquid to solid III and solid IV phase have been determined. All the nine elastic constants in orthorhombic structure phase IV were presented for the first time, each elastic constant grows monotonously with pressure and a crossover of the off‐diagonal moduli C₁₂ and C₁₃ was observed at around 12 GPa because of their different pressure derivative values. We also performed ab initio simulations to calculate the bulk elastic moduli for orthorhombic ammonia, the calculated bulk moduli agree well with experimental results. In Raman spectra the very weak bending modes ν₂ and ν₄ for orthorhombic ammonia are both observed at room temperature, a transition point near 12 GPa is also found from the pressure evolution of the Raman bands. Copyright © 2011 John Wiley & Sons, Ltd.     

Sm富勒烯的芯态光电子能谱

用X射线光电子能谱研究了Sm掺杂的固态C₆₀相衍变和芯电子态.在Sm_xC₆₀中Sm的含量x小于0.5时，样品是固溶相；在x=0.5和x=2.75之间的掺杂阶段，样品是这两个相的混合.在x=2.75和x=6之间的高掺杂阶段未观察到相分离的X射线光电子能谱证据.Sm 4f, 4d的实验数据表明Sm的价态是+2.二价Sm 3d_5/2芯态谱线存在两个子峰. 关键词： 60的Sm填隙化合物')" href="#">C₆₀的Sm填隙化合物 相结构 电子态 X射线光电子能谱     

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     

Zero-field μSR in crystalline C60

The C_o60Mu radical in polycrystalline C₆₀ has been studied in zero magnetic field between 9 K and 200 K, and at room temperature. At low temperatures, we observe three low-frequency oscillations which correspond to the intra-triplet transitions of a completely anisotropic muon-electron hyperfine interaction. These signals exhibit a strongly temperature-dependent T₁, attributed to thermally-activated jump rotational diffusion of the C₆₀Mu radical. A fit to an Arhenius law yields an activation energy of 200(20) meV for temperatures below the fcc-sc structural phase transition. At room temperature only the motionally-narrowed 325 MHz singlet-triplet transition is observed.     

预注入对Si1-xCx合金形成的影响

室温下在单晶Si中注入(0.6—1.5)at%的C原子,部分样品在C离子注入之前在其中注入²⁹Si⁺离子产生损伤,然后在相同条件下利用高温退火固相外延了Si_1-xC_x合金,研究了预注入对Si_1-xC_x合金形成的影响.如果注入C离子的剂量小于引起Si非晶化的剂量,在950℃退火过程中注入产生的损伤缺陷容易与C原子结合形成缺陷团簇,难于形成Si_1-xC关键词： 离子注入 固相外延 1-xC_x合金')" href="#">Si_1-xC_x合金     

Physical and mechanical properties of C60 under high pressures and high temperatures

The physical and mechanical properties of a C₆₀ fullerene sample have been investigated under high pressure–high temperature conditions using a designer Diamond Anvil Cell. Electrical resistance measurements show evidence of C₆₀ cage collapse at 20 GPa, which leads to the formation of an insulating phase at higher pressure. Energy dispersive X-ray diffraction (EDXD) data indicated that the characteristic fcc reflections gradually decrease in intensity and eventually disappear above 28 GPa. A C₆₀ sample was laser-heated at a pressure of 35 GPa to a temperature of 1910±100 K and, subsequently, decompressed to ambient conditions. The photoluminescence spectra and the Raman spectrum of the pressure–temperature-treated sample were measured at a low temperature of 80 K. Raman peak at 1322.3 cm^?1 with full-width half-maximum of 2.9 cm^?1 was observed from the sample, which is attributed to the hexagonal diamond phase in the sample. The room temperature photoluminescence spectra showed a symmetric emission band centered in the red spectral range with a peak at 690 nm. The structural analysis of the pressure–temperature-processed C₆₀ sample using EDXD method showed strong internal structure orientation and a phase close to hexagonal diamond. Mechanical properties such as hardness and Young’s modulus were measured by nanoindentation technique and the values were found to be 90±7 and 1215±50 GPa, respectively and these values are characteristic of sp³-bonded carbon materials.     

C60分子在有序-无序和玻璃态相变间的取向概率与弛豫行为

用极限动力学模型研究了Ｃ₆₀分子在有序-无序相变和玻璃态相变温度区间取向 角为98°和38°的取向概率与温度的关系.计算结果在玻璃态相变点附近的85K,90K和有序- 无序相变点的260K分别与实验值相吻合,取向概率对实验值更精确的拟合及其对温度的二阶 导数预言玻璃态相变点在84K.导出了弛豫规律,其结果表明：双能级的Ｃ₆₀分子从非平衡态到平衡态的弛豫行为与非指数因子β有关,其总的弛豫时间决定于其中一个较 短的弛豫时间,展宽指数形式保持不变.讨论了KWW方程的非 关键词： 60')" href="#">Ｃ₆₀ 取向概率 非平衡态弛豫     

Magnetic entropy change and magnetic phase transition of LaFe11.4Al1.6Cx （x=0-0.8） compounds

The unit cell volume and phase transition temperature of LaFe11.4Al1.6Cx compounds have been studied. The magnetic entropy change, refrigerant capacity and the type of magnetic phase transition are investigated in detail for LaFe11.4Al1.6Cx with x=0.1, All the LaFe11.4Al1.6Cx （x=0-0.8） compounds have the cubic NaZn13-type structure. The addition of carbon atoms brings about a considerable increase in the lattice parameter. The bulk expansion results in the change of phase transition temperature （Tc）, Tc increases from 187K to 269 K with x varying from 0.1 to 0.8, Meanwhile an increase in the lattice parameter can also cause a change of the magnetic ground state from antiferromagnetic to ferromagnetic. Large magnetic entropy change IASI is found over a large temperature range around Tc and the refrigerant capacity is about 322J/kg for LaFe11.4Al1.6C0.1. The magnetic phase transition belongs in weakly first-order one for x=0.1.     

Coexistence of magnetic and ferroelectric properties in Y0.1Co1.9MnO4

The magnetic,conductivity,and dielectric properties have been investigated in single-phase polycrystalline Y0.1 Co1.9 MnO4.The temperature-dependent magnetisation reveals the ferromagnetic transition in sample at a low temperature (～186 K).Magnetisation as a function of field H (M-H loop) indicated the weak ferromagnetism of the sample at room temperature.The constant ε and dielectric loss tgδ measurements represent a ferroelectric phase transition at a higher temperature (～650 K),while the conductivity shows an insulator-metallic transition.The ferroelectric hysterisis loops and capacitance-voltage measurements confirm the ferroelectric nature of the sample at room temperature.The observed ferromagnetism and ferroelectric nature in this material suggests a potential multiferroic application.     

Complete pentagon orientational ordering in C60 fullerite charged with NO

Solid C₆₀ was stored in NO under high pressure, and the gas molecules NO were found to diffuse into the octahedral interstitial sites in its fcc crystal lattice. Its ¹³C NMR MAS spectra are composed of a primary resonance at 143.7 ppm accompanied by two minor peaks shifted 0.4 and 0.8 ppm downfield, respectively. The dopant was found to depress its phase transition temperature at 260 K in pure C₆₀ and to substantially reduce the drop Δ?′ at the phase transition temperature. Furthermore, the spectral features associated with relaxation during glass transition at lower temperature, as observed in impedance spectra, were smeared. The fraction of P-orientation below T _c was calculated to be larger than 11/12. These results show that a completely P-oriented phase occurred in (NO)_0.1C₆₀ and that this phase is favored by a negative pressure on the C₆₀ lattice exerted by NO, as well as by the electrostatic interaction between the two.     

Comparative study of optical parameters of fullerene C60 film at different temperatures

Fullerene C₆₀ thin films on glass substrate (around 2000 ? thickness) were prepared by thermal evaporation technique. The structural, surface morphology and optical properties of the films were studied. The optical properties of fullerene C₆₀ were investigated in the spectral range 200 nm to 900 nm using a UV-Vis spectrophotometer at room temperature as well as at liquid nitrogen temperature (77 K). The optical band gap at room temperature is found to be 2.30 eV, which gradually decreases with lowering the temperature and reaches to 2.27 at 77 K. The thickness and refractive index of fullerene C₆₀ film were calculated by ellipsometry. From the X-ray analysis, we have calculated the grain size, dislocation density, number of crystallite per unit area, and strain of the film at room temperature. The surface morphology of film was analyzed by scanning electron microscope (SEM). The present result show that the fullerene C₆₀ film becomes more conducting at low temperature.     

Pressure-induced transformations and optical properties of the two-dimensional tetragonal polymer of C60 at pressures up to 30 GPa

The Raman spectra of the two-dimensional tetragonal (2D(T)) polymeric phase of C₆₀ have been studied in situ at pressures up to 30 GPa and room temperature. The pressure dependence of the phonon modes shows an irreversible transformation of the material near 20 GPa into a new phase, most probably associated with the covalent bonding between the 2D polymeric sheets. The Raman spectrum of the high-pressure phase is intense and well resolved, and the majority of modes are related to the fullerene molecular cage. The sample recovered at ambient conditions is in a metastable phase and transforms violently under laser irradiation: the transformed material contains mainly dimers and monomers of C₆₀ and small inclusions of the diamond-like carbon phase. The photoluminescence spectra of the 2D(T) polymer of C₆₀ were measured at room temperature and pressure up to 4 GPa. The intensity distribution and the pressure-induced shift of the photoluminescence spectrum drastically differ from those of the C₆₀ monomer. The deformation potential and the Grüneisen parameters of the 2D(T) polymeric phase of C₆₀ have been determined and compared with those of the pristine material.     

Magnetocaloric effect in Gd6Co1.67Si3 compound with a second-order phase transition

The magnetic properties and the magnetic entropy change AS have been investigated for Gd6Co1.67Si3 compounds with a second-order phase transition. The saturation moment at 5 K and the Curie temperature TC are 38.1μB and 298 K, respectively. The AS originates from a reversible second-order magnetic transition around TC and its value reaches 5.2 J/kg.K for a magnetic field change from 0 to 5T. The refrigerant capacity （RC） of Gd6Co1.67Si3 are calculated by using the methods given in Refs.[12] and [21], respectively, for a field change of 0 5T and its values are 310 and 440 J/kg, which is larger than those of some magnetocaloric materials with a first-order phase transition.     

偏硼酸钡低温相晶体在高压下的电学性质与相变

 在金刚石压砧装置上，采用电容和电阻测量方法研究了偏硼酸钡低温相晶体（β-BaB₂O₄）在室温下和16 GPa内的电容、电阻与压力的关系。实验结果表明，它的电容在2.1、4.6、6.4、8、9.5、10.7 GPa左右都有一个突变。这说明β-BaB₂O₄内部的结构状态在这些压力下都发生了变化，可能发生了相变。还发现β-BaB₂O₄样品在较高压力下已发生了非晶化转变，而且是不可逆的，在卸压后被保留下来。这个非晶化转变的压力大约在11~12 GPa。     

A luminescence study of B-type Eu2O3 under pressure

Abstract

Luminescence spectra from Eu³ + ion in B-type (monoclinic) ₂O₃ powder have been recorded at room temperature as a function of pressure using a diamond anvil cell. Changes in the spectral pattern of the Eu³ + ion emission at about 4 GPa indicated that a phase transition to the A-type (hexagonal) structure had taken place. Upon release of the applied pressure, the B-type structure was regained with hysteresis. The spectral shifts with pressure have been used to study the effect of pressure on the spin-orbit interaction of the 4f electrons in the Ed + ion. The relationship between the relative changes in the spin-orbit coupling constant, ζ_4f, and the volume accompanying the phase transition is also discussed.     

Nd0.5Sr0.4Pb0.1MnO3的结构和磁性

通过室温下的中子衍射和磁性测量对多晶样品Nd_0.5Sr_0.4Pb_{0 .1}MnO₃ 的结构和磁性进行了实验研究.中子衍射结果表明，该样品具有正交的钙钛矿结构，空间群 是Pnma，即结构发生了晶场畸变.由M-T和R-T曲线可知，居里温度T_C=273 K ，其特征是随着温度的增加样品经历了从铁磁金属态转变到顺磁半导态，且转变温度T _p＝225 K；用锰氧化物晶场和双交换作用的竞争解 关键词： 结构 磁性 中子衍射 晶场畸变 p')" href="#">转变温度T_p 双交换作用