Volume compression of thallium to 45 GPa

Abstract

High-pressure structural transition and volume compression for thallium were investigated to 45 GPa in a diamond anvil cell using the angular dispersive X-ray diffraction technique. Except for the known polymorphic transition at 3.7 GPa, no other structural change was observed in this pressure range. The equation of state of the high pressure phase has been obtained: its initial bulk modulus, B₀ = 33.1 GPa, is lower by 10% than that of the hexagonal phase at normal pressure.     

High pressure studies up to 50GPa of CuO

Abstract

Copper oxide has been studied at high pressure up to 50 GPa. A monoclinic structure was compatible with the measurements at all pressures, and no phase change was observed. A bulk modulus, B₀, = 98 GPa, and its pressure derivative B′₀ = 5.6 was obtained.     

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。     

X-ray diffraction study of molybdenum diselenide to 35.9 GPa

In situ high-pressure angle dispersive synchrotron X-ray diffraction studies of molybdenum diselenide (MoSe₂) were carried out in a diamond-anvil cell to 35.9 GPa. No evidence of a phase transformation was observed in the pressure range. By fitting the pressure-volume data to the third-order Birch-Murnaghan equation of state, the bulk modulus, K_0T, was determined to be 45.7±0.3 GPa with its pressure derivative, K′_0T, being 11.6±0.1. It was found that the c-axis decreased linearly with pressure at a slope of −0.1593 when pressures were lower than 10 GPa. It showed different linear decrease with the slope of a −0.0236 at pressures higher than 10 GPa.     

Compressibility of hydrogen in Ni and Re hosts at pressures to 123 GPa

Abstract

Ni-H and Re-H binary systems have been studied at room temperature by X-ray diffraction in a diamond-anvil cell. The formation of the hydrides NiH and ReHo.4 with no change in the types of the host metal lattices was observed through the expansion of the host lattices. No structure changes were observed in the metal sub-lattice of either hydride under increasing pressure and the equations of state have been obtained to 123GPa. The difference in the partial hydrogen volume as a function of pressure between the Ni-H and Re-H systems can be understood with reference to the behaviour of conduction electrons. The pressure dependence of the partial hydrogen volume in these hydrides supports the hypothesis of the apparent common-volume behaviour of hydrogen in a metallic environment.     

Shock-induced phase transitions in the MgO-FeO system to 200 GPa

We report new shock-compression data for single-crystal MgO at 114 and 192 GPa. Our data together with the existing shock-wave data revealed a volume discontinuity at 170±10 GPa along with the MgO Hugoniot. The discontinuity gives a volume increase of 1.9%, indicating a possible phase transition from a rock-salt structure (B1) to a high-temperature phase along with the MgO Hugoniot. We re-examined the Hugoniot data on polycrystalline sample (Mg_0.6, Fe_0.4)O up to 200 GPa [M.S. Vassiliou, T.J. Ahrens, The equation of state of Mg_0.6Fe_0.4O to 200 GPa, Geophys. Res. Lett. 9 (1982) 127-130], which showed similar discontinuity with a 2.2% volume increase at 135±10 GPa. Our results add to fundamental understandings of the behavior of MgO and the lower mantle mineral magnesiowüstite (Mg, Fe)O at ultrahigh pressure and temperature.     

Shock-wave compression of hydrogen to pressures of 65 GPa

The results of experiments on determining the shock-wave compression of initially solid hydrogen (protium) in the pressure range from 17 to 66 GPa are reported. The data have been obtained by using spherical explosive charges. Pressure in samples is created by the impact of a steel striker accelerated to maximum velocities of 23 km/s. Gaseous protium is converted to the solid state using a special cryogenic cooling system.     

In situ X-ray diffraction study of germanium at pressures up to 11 GPa and temperatures up to 950 K

In situ X-ray diffraction measurements on germanium were conducted in the pressure range of 5-11 GPa and temperatures up to 950 K. Using our data a better defined P-T diagram for germanium is presented. The coordinates of the triple point between Ge_I-Ge_II-Ge_L have been determined to a better degree of precision. The onsets of the Ge_I-Ge_II transition were found both under hydrostatic and non-hydrostatic conditions. Anisotropy of thermal expansion coefficient for the Ge_II is characterized from the c/a ratios in the temperature interval 473-823 K. Phases Ge_III and Ge_IV are shown to be metastable forms of germanium.     

Quasi-isentropic compression of liquid argon up to 500 GPa

The compressibility of liquid argon up to pressures ∼500 GPa has been investigated experimentally. The argon was compressed by a cylindrical shell accelerated by the detonation products of an explosive. The density was recorded by the gamma-graphic method and the pressure was determined from the gas-dynamic calculations. Comparing the experimental and computational results showed that the compression process studied is isentropic to a quite high degree. The compression of liquid argon up to a density of 7.3 g/cm³ did not show any clear anomalies associated with a structural transition or metallization. Zh. éksp. Teor. Fiz. 111, 2099–2105 (June 1997)     

Pressure-volume relations for Zn,Cd, Ga,In and TI at room temperature to 30 GPa and above

Abstract

The elemental metals Zn, Cd, Ga, In and TI are studied by energy dispersive X-ray diffraction under pressures up to 30 GPa and above. Room temperature equation of state (EOS) data are derived and compared with results of earlier static and dynamic measurements at lower and higher pressures, respectively.     

First-principles calculations of the structural, electronic, and optical properties of LiF up to 300 GPa

The structural, electronic, and optical properties of LiF are investigated at high pressures using the plane-wave pseudo-potential density functional method (DFT) within the generalized gradient approximation (GGA). From the analysis of Gibbs free energies, we find that no phase transition takes place for LiF in the presented pressure range from 0 to 300 GPa. The result is consistent with the theoretical prediction obtained from the ab initio calculations [N.A. Smirnov, Phys. Rev. B 83 (2011) 014109] that the rock-salt structure is thermodynamically stable up to 1000 GPa. Meanwhile, good agreement between the calculated equation of state parameters and the experimental results is obtained, and a direct energy gap of 8.65 eV is estimated in the DFT-GGA for LiF with rock-salt structure. In addition, the dielectric function and optical properties such as reflectivity, absorption coefficient, and refractive index dependence of the photon energy from 0 to 50 eV and wavelength from 0 to 200 nm at different pressures are also calculated and analyzed. It is found that the rock-salt LiF is transparent from the partially ultra-violet to the visible light area and hardly is the transparence affected by the pressure. Furthermore, the curve of optical spectrum will shift to high energy area with increasing pressure.     

High pressure X-ray diffraction experiments on NpS and PUS up to 60 GPa

Abstract

Neptunium and plutonium monosulfides were studied under high pressure up to ～60 GPa using a diamond anvil cell in an energy dispersive X-ray diffraction facility. The compounds, of cubic rock salt structure type at ambient pressure, do not show any crystallographic phase transition in the domain of investigation. From the pressure-volume relationship, we determined bulk moduli of 92 and 120 GPa with pressure derivatives of 4.6 and 4.1 for NpS and PUS respectively.     

Optical properties of methane to 288 GPa at 300 K

Optical properties of solid methane (CH₄) were studied at high pressure and room temperature using a diamond anvil cell. Reflectivity and transmission measurements were used to measure the refractive index to 288 GPa. Fabry-Perot interferometery was used to measure the sample thickness to 172 GPa. This data was fitted to the derived expression of thickness vs. pressure that was then used to calculate the thickness to 288 GPa. This in turn was combined with optical absorption experiments to obtain the absorption coefficient and hence the extinction coefficient k^*. From combined reflection and absorption experiments the refractive index n=n_s+ik^* was obtained. The index of refraction and the ratio of molar refraction to molar volume showed a large increase between 208 and 288 GPa. This behavior indicated that a phase transformation of insulator-semiconductor might have occurred in solid CH₄ by 288 GPa.     

Electrical conductivity of water during quasi-isentropic compression to 130 GPa

The specific electrical conductivity Σ of water was measured during multistage shock loading to pressures of 12–130 GPa. At maximum pressure the density of the water was 3.2 g/cm₃. Three or four pressure discontinuities could usually be resolved experimentally and the value of Σ was determined in each of these. As the pressure was increased in this range, the value of Σ increased from 1.2 to approximately 150 S/cm. In electro-chemical experiments, galvanic cells having electrodes of various metals and water as the electrolyte were subjected to dynamic compression. The characteristics of the recorded emf of these cells indicate that the high electrical conductivity of highly compressed water is of an ionic nature.     

On the formation of photoinduced high pressure phases in sulfur below 10 GPa

Abstract

We investigate the phase transformations in sulfur for pressures up to 10 GPa by time resolved Raman spectroscopy. The transition to the photosensitive phase p-S is stimulated by the blue laser line between 3 and 9 GPa. The kinetics of this transition as derived from the time evolution of the intensities of characteristic Raman excitations shows the typical features of an activated first order phase transition. This transformation proceeds via a disordered (amorphous) intermediate state.

Above 9 GPa a further phase change to S, is kinetically characterized and follows similar rules i.e. the integral intensities of selected S, Raman lines exhibit a sigmoidal time dependence. In both high pressure phases a broad Raman excitation between 800 and 1000 cm^?1 is observed.     

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。     

A high pressure raman study of ThO2 to 40 GPa and pressure-induced phase transition from fluorite structure

The pressure dependence of the first-order Raman peak and two second-order Raman features of ThO₂ crystallizing in the fluorite-type structure is investigated using a diamond anvil cell, up to 40GPa. A phase transition from the fluorite phase is observed near 30 GPa as evidenced by the appearance of seven new Raman peaks. The high pressure phases of ThO₂ and CeO₂ exhibit similar Raman features and from this it is believed that the two structures are the same, and have the PbCl₂-type structure. The pressure dependence dω/dP of the observed phonons and their mode Grüneisen parameters are similar to the isostructural CeO₂. The observed second-order Raman features are also identified from the calculated phonon dispersion curves for ThO₂.     

Solidification of selenium melt under pressure up to 6.5 GPa

Abstract

High purity selenium samples were melted under high pressure (≤6.4 GPa) and quenched at various rates ranging from 2 K s^?1 to 500 K s^?1 and the recovered material was examined by X-ray diffraction and electron microscopy. In the entire range of pressure and cooling rate, the melt was found to solidify into a polycrystalline aggregate of the trigonal phase of selenium. The samples obtained by slow cooling of the melt at 6.4 GPa contain, in addition to crystalline phase, regions which appear to be amorphous.     

Shock compression of deuterium near 100 GPa pressures

The shock-compression curve (Hugoniot) of D2 near 100 GPa pressures (1 Mbar) has been contro-versial because the two published measurements have limiting compressions of fourfold and sixfold. Our purpose is to examine published experimental results to decide which, if either, is probably correct. The published Hugoniot data of low-Z diatomic molecules have a universal behavior. The deuterium data of Knudson et al. (fourfold limiting compression) have this universal behavior, which suggests that Knudson et al. are correct and shows that deuterium behaves as other low-Z elements at high tem-peratures. In D2, H2, N2, CO, and O2, dissociation completes and average kinetic energy dominates average potential energy above approximately 60 GPa. Below approximately 30 GPa, D2, H2, N2, CO, and O2 are diatomic. D2 dissociation is accompanied by a temperature-driven nonmetal-metal transition at approximately 50 GPa.