高压下金红石的拉曼光谱分析

常温下利用金刚石压腔装置(DAC)对金红石加压至40GPa,进行拉曼光谱的原位分析.发现压力约为13GPa时,金红石结构转变为斜锆石结构(ZrO2).21.1GPa相变完全.直至实验最高压力,没有进一步相变出现.在卸压中,斜锆石结构转变为α-PbO2结构.实验压力通过红宝石用拉曼光谱测压的计算方法确定,快速方便.     

High Pressure Theoretical Studies of Actinide Dioxides

Actinide dioxides (ThO 2 , UO 2 , Pu 2 etc.) compounds have the CaF 2 -type structure at ambient pressure and temperature. Under high pressure, they exist in the PbCl 2 -type structure, belonging to space group Pnma [1]. We have studied crystal structures under high pressure in actinide dioxides by means of first-principles self-consistent total-energy calculations with the non-local Perdew, Burke and Ernzerhof (PBE) exchange correlation using the full-potential linear-muffin-tin-orbital (FPLMTO) method. The atomic equilibrium volume, bulk modulus and transition pressure for actinide dioxides were calculated, covering the full pressure range for which the mentioned experiments have been done [2].     

Observation of the Cinnabar Phase in ZnSe at High Pressure

In this paper we describe the results of an energy dispersive X-ray diffraction experiment carried out in the ZnSe 1 m x Te x alloy and pure ZnSe under high pressure. In the downstroke the cinnabar phase is observed between the rocksalt and the zincblende phases. The analysis of the whole series of compositions ( x =0, 0.05, 0.1 and 0.2) enables us to establish its lattice parameters in ZnSe ( a =3.785 + and c =8.844 + at 10.5 GPa). The X-ray diffraction pattern simulation suggests that the internal parameters u and v are close to 0.5, indicating that the cinnabar phase in ZnSe is similar to that observed in GaAs and ZnTe. The cinnabar's stability range decreases as the Te content is reduced.     

Pressure Study on New Superconducting Germanium Clathrates

We investigate the low temperature properties of the recently discovered clathrates Ba 6 Ge 25 and Na 2 Ba 4 Ge 25 by tuning both materials with hydrostatic pressure. At ambient pressure, Ba 6 Ge 25 undergoes a two-step structural phase transition between 230 K and 180 K from metallic behavior to a high-resistivity state. A superconducting transition occurs at T_{C}\approx 0.24\,\hbox{K} out of the resulting bad metal ( \rho_{0}\approx 1.5\,\hbox{m}\Omega\;\hbox{cm} ). With increasing pressure, the structural phase transition is shifted to lower temperature but T C increases drastically. T C reaches a maximum value of 3.85 K at the critical pressure p_{C}\approx 2.8\,\hbox{GPa} , where the structural distortion is completely suppressed and the system exhibits metallic behavior. On replacing 1/3 of the Ba atoms with Na (Na 2 Ba 4 Ge 25 ), no structural transformation is observed below room temperature, and the superconducting transition temperature is higher (T_{C}(p = 0) \approx 1.05\,\hbox{K}) than in the undoped case at ambient pressure but decreases slightly with increasing pressure.     

Electrical properties and Tc of CaLaBaCu3Ox at pressures up to 9 GPa

Abstract

By means of a four-point resistivity method the critical temperature (T_c) of the tetragonal high temperature super-conductor CaLaBaCu₃O_x was studied for pressures up to 9 GPa. The pressure dependence of T_c is small and negative, dT_c/dp = - 0.77 K/GPa, and agrees with the general trend observed in previous data.     

Suppression of Jahn-Teller Distortion and Insulator-To-Metal Transition in LaMnO 3 at High Pressures

Structural, vibrational and electronic properties of LaMnO 3 under pressures up to 38 GPa have been studied by synchrotron X-ray powder diffraction, Raman spectroscopy, optical reflectivity, and transport measurements. The cooperative Jahn-Teller distortion of the MnO 6 octahedra of the perovskite-type structure is continuously suppressed with increasing pressure, a process which appears completed at ～20 GPa. The system remains insulating to 32 GPa, where an insulator-metal transition is observed. This transition is attributed to strengthened Mn--O--Mn interactions due to the increasing overlap of atomic orbitals.     

Effect of pressure on magnetic phases of (Fe1-x Ni x )49Rh51

The effect of high pressure and magnetic field on the stability of magnetic phase transitions in (Fe_1?x Ni _x )₄₉Rh₅₁ has been studied. It has been shown that the increase in the Ni content suppresses the stability of the low-temperature antiferromagnetic phase and leads to its disappearance. Pressure on the other hand restores the stability to the antiferromagnetic order. These findings are explained using first-principles band-structure calculations.     

297 K和0.13～1 GPa压力下菱镁矿的拉曼光谱实验研究

在T=297 K,130 MPa＜P＜967 MPa下用拉曼光谱对菱镁矿1 094 cm-1峰随压力变化关系进行了测量,结果表明随着压力增大,1 094 cm-1峰往高波数方向移动,其波峰位置与压力关系为：ν(cm-1)=0.007 44×P(MPa)+1 093.3。在T=297 K,130 MPa＜P＜967 MPa时,菱镁矿可用作地质压力计。压力与菱镁矿1 094 cm-1峰偏移量关系为：P(MPa)=125.8×(Δν_p)_{1 094}+124.7,(1 094 cm-1＜ν_p＜1 101 cm-1)。在实验的压力范围内未观察到菱镁矿的相变和有机物的生成。     

Pressure Induced Phase Transition in Solid Oxygen at 1.8 K

Pressure dependence of Raman scattering in solid oxygen was studied at 1.8 K. When the f phase is compressed, two libron peaks that, increasing pressure, merge smoothly with those of the l phase at 8 GPa are observed around 5 GPa, besides the libron peaks due to the f phase. Furthermore, unknown Raman peaks are also observed at 5-9 GPa. Coexistence of these Raman peaks indicates that the pressure region from 5 to 9 GPa at low temperature does not correspond to a single phase but complicated mixed ones including f and l components.     

常温及常压至1.2GPa条件下异辛烷的拉曼光谱研究

利用碳化硅压腔在室温(25℃)下,研究了异辛烷(2,2,4-三甲基戊烷)在常压至1.2GPa条件下的拉曼光谱特征。研究结果表明,异辛烷CH2和CH3的碳氢伸缩振动的拉曼位移随着压力的增大均呈线性向高频方向移动,其拉曼位移与压力的函数关系为:ν2 873=0.002 8P+2 873.3;ν2 905=0.004 8P+2 905.4;ν2 935=0.002 7P+2 935.0;ν2 960=0.012P+2 960.9。在1.0GPa附近,异辛烷的拉曼位移出现突变,与显微镜下观察发生的异辛烷液-固相变一致。结合异辛烷在常压下的熔点数据,获得了异辛烷的液-固两相相图,并根据克拉贝龙方程获得了液-固相转变过程中的摩尔体积变化量ΔVm=4.46×10-6 m3.mol-1和熵变ΔS=-30.32J.K-1.mol-1。     

Optical Spectroscopic Study of Al 2 O 3 : Ti 3+ Under Hydrostatic Pressure

This work investigates the effect of hydrostatic pressure on the excitation, emission and lifetime of Ti 3+ - doped Al 2 O 3 in the 0-110 kbar range. The application of pressure induces band shifts that are correlated with the corresponding local structural changes undergone by the TiO 6 complex. The increase of the Stokes-shift and the reduction of the Jahn-Teller (JT) splittings under pressure are analysed in terms of a simple model based on linear electron-phonon couplings to the a_{1_{\rm g}} and the JT e g vibrational modes.     

Xanes and raman spectroscopy under pressure of bromobenzene

Abstract

The behaviour of bromobenzene (BBe) compressed in a diamond anvill cell up to 30 GPa was studied by XANES and Raman spectroscopy. The liquid-solid transition and a solid-solid transition were observed at 0.9 GPa and 9 GPa respectively. Above 24 GPa, an irreversible transformation occurs to a solid orange-yellow compound which can be recovered at zero pressure. The polymerization mechanism, in connection with the occurence of Br-bonded Sp² and Sp³ carbons in the solid compound, is discussed.     

Non-Conventional Behaviour of Castor Oil Under High Pressure

Castor oil shows non-conventional physical and chemical behaviour when submitted to pressure. This paper gives a brief presentation of the specific physical properties of castor oil under pressure up to 1.0 GPa. The changes of permittivity, dielectric loss and the structure of the high-pressure induced phases of castor oil are also described.     

压力高达27 GPa下天然奥长石的XRD分析

在室温高达27 GPa压力下对天然奥长石(Na_0.86K_0.02Ca_0.12Mg_0.01(Fe_0.01Al_1.12Si_2.87O₈))粉晶进行了原位同步辐射X光衍射(XRD)测量,获得了样品的状态方程。实验数据表明随着压力增大奥长石样品在大约3.5 GPa发生了三斜向单斜的相变(P1→C2)和在大约10.0 GPa发生了单斜对称相变(C2→C2/m)。样品三个相的体模量计算值分别为K₀=73.8 GPa (K′=10.98), K_(C2)=124 GPa (K′=1.05) 和K_(C2/m)=272 GPa (K′=0.625)。样品的元素组成影响其T-O-T 键角的刚度、M-O键的强度和Si-O-Al键角的弯曲,从而导致奥长石样品在高压行为的特殊变化。三斜相的奥长石晶胞压缩性具明显的各向异性。实验结果表明在冷俯冲带奥长石可能是碱金属和碱土金属深循环的载体。     

Pressure Dependence of the Transport and Magnetic Properties of Colossal Magnetoresistance Tl 2 Mn 2 O 7 Pyrochlore System

The Tl 2 Mn 2 O 7 pyrochlore system, pure or doped at the Tl position (Cd, Bi, Sc) or at Mn position (Sb, Te, Cr, Pb), present interesting magnetotransport properties characterized by the Colossal Magnetoresistance (CMR) effect. Our data for Tl 2 Mn 2 O 7 and Tl 1.9 Bi 0.1 Mn 2 O 7 indicate a decrease of the ordering temperature, measured from resistivity and magnetic susceptibility up to 70-90 kbars, with a clear increase of T C for higher pressures (up to 120 kbars). By contrast, in the case of Tl 2 Mn 1.8 Sb 0.2 O 7 , T C increases with pressure in the explored pressure range. A recent theory from Nuñez-Regueiro and Lacroix explains this dependence in terms of the existence of a second coupling mechanism between Mn ions, mediated by the conduction band (Tl (6s)). The doping at the Mn position (Sb) strongly increases the charge carrier density, so that this second coupling mediated by the conduction band, is strongly enhanced, in such a way that T C increases with pressure.     

Properties of shock-compressed liquid krypton at pressures of up to 90 GPa

The following quantities of shock-compressed liquid krypton are measured behind a plane shock front at pressures up to 90 GPa: compressibility up to densities of 7 g/cm³, brightness (color) temperatures of 6000–24000 K, and electrical conductivities of 40–60000 (Ω·m)⁻¹. X-t diagram methods are used to estimate sound speeds of up to 5.5 km/s at pressures of 30–75 GPa. The optical absorption coefficients in the violet and red (30–300 cm⁻¹) are measured at pressures of 20–90 GPa from the rise in brightness of the shock front luminosity. The optical reflection coefficient of the shock front (∼13%) at a pressure of 76.1 GPa is measured for the first time. Zh. éksp. Teor. Fiz. 116, 551–562 (August 1999)     

High-Precision Studies of the Compressibility and Relaxation of g-As2S3 Glasses at High Hydrostatic Pressures up to 8.6 GPa

Journal of Experimental and Theoretical Physics - The high-precision volume measurements of the g-As2S3 glass have been performed at high hydrostatic pressures up to 8.6 GPa, and room temperature....     

Measurement of Seebeck effect (thermoelectric power) at high pressure up to 40 GPa

The paper reports details of a high-pressure thermoelectric power (Seebeck effect) technique up to 40 GPa. Several different types of high-pressure cells with anvil insets are presented. The technique was applied for measurements of pressure dependence of the thermopower of several substances including elemental metals (lead, Pb; indium, In), cerium-nickel alloy, Ce-Ni and sulphur, S. Two peculiarities in the pressure dependences of the thermopower of CeNi were found and attributed to structural transformations, near ∼5 and ∼10 GPa. These transitions were confirmed in direct X-ray diffraction studies. Sulphur compressed to 40 GPa exhibited a hole type conductivity and the thermopower value was about ∼+1 mV/K. Additionally, as an example of pressure calibration, the data on the electrical resistivity of zinc selenide, ZnSe, are given in a range of 0-23 GPa. These data suggest three possible scenarios of phase transitions from a rock salt (RS) high-pressure phase of ZnSe under decompression: RS→zinc blende (ZB), RS→cinnabar→ZB, and RS→wurtzite.     

High Temperature-High Pressure Structural Studies of Cerium

Energy dispersive X-ray-diffraction with the large volume press MAX 80 at HASYLAB/DESY is used in the present study for the determination of the p - V - T -relations around the critical point of the f - n -phase transition in Cerium. Furthermore the f - l -phase boundary is studied experimentally to remove the last question marks from the phase diagram of Cerium in the accessible region of pressure and temperature.