Gold under high pressure

Abstract

First principle predictions for the equation of state of gold using solid and liquid state theories are compared up to combined pressures and temperatures of 600 GPa and 17 000 K with static diamond anvil cell compression, ultrasonic measurements and shock Hugoniot data which include a recent laser driven shock Hugoniot points at 600 GPa. Excellent agreement between theoretical and experimental data is observed. The theoretically estimated 300 K isotherm agrees to within 2 GPa with the isotherm that has been measured to 70 GPa using the diamond anvil cell. The structural energy estimates show that the normal f.c.c. phase remains stable under pressure. The estimate of the shock Hugoniot temperature of gold at 600 GPa based on a liquid state model is consistent with the measurements of laser induced shock luminescence, which in fact provides an experimental determination of the temperature of gold above its Hugoniot melting point. The powerful means provided by theory in the prediction of material properties of gold at ultra high pressures and temperatures is significant because gold is an efficient converter of laser energy into soft X-rays and is a potential candidate as a standard for high pressure, high temperature work.     

In situ observation of pressure-induced electrical resistance changes in zirconium: pressure calibration points for the large volume press at 8 and 35 GPa

Simultaneous in situ pressure–resistance measurements were carried out up to 40 GPa using a multianvil apparatus with synchrotron-based X-ray diffraction (XRD) measurements. Pressure-induced electrical resistance changes in zirconium were measured at ambient temperatures and two discontinuities were observed around the α–ω and ω–β structural phase transitions. The transition pressures were strictly determined from simultaneous measurements of the electrical resistance and in situ XRD as 7.96±0.16 and 34.5±0.3 GPa, respectively, using an equation of state for gold as the pressure scale. The precisely determined transition pressures are available for room temperature pressure calibration points for large volume presses installed at offline laboratories.     

Unexpected high stiffness of Ag and Au nanoparticles

We studied the compressibility of silver (10 nm) and gold (30 nm) nanoparticles, n-Ag and n-Au, suspended in a methanol-ethanol mixture by x-ray diffraction (XRD) with synchrotron radiation at pressures up to 30 GPa. Unexpectedly for that size, the nanoparticles show a significantly higher stiffness than the corresponding bulk materials. The bulk modulus of n-Au, K(0)=290(8) GPa, shows an increase of ca. 60% and is in the order of W or Ir. The structural characterization of both kinds of nanoparticles by XRD and high-resolution electron microscopy identified polysynthetic domain twinning and lamellar defects as the main origin for the strong decrease in compressibility.     

高压下γ'-Fe4N晶态合金的声子稳定性与磁性

利用基于密度泛函理论的第一性原理研究了高压下有序晶态γ’-Fe₄N合金的晶格动力学稳定性与磁性. 对比没有考虑磁性的γ’-Fe₄N的声子谱, 得出压力小于1 GPa时, 自发磁化诱导了铁磁相γ’-Fe₄N基态晶格动力学稳定. 压力在1.03-31.5 GPa时, Σ线上的点(0.37, 0.37, 0)、对称点X和M 上相继出现了声子谱软化现象. 压力在31.5-60.8 GPa时, 压致效应与自发磁化对诸原子的作用达到了稳定平衡, 表现出了声子谱稳定. 压力大于61.3 GPa时, 随着压力的增大压力诱导体系动力学不稳定性越强. 通过软模相变理论对于γ’-Fe₄N, 在10 GPa下的声学支声子的M点处软化现象的处理, 发现了动力学稳定的高压新相P2/m-Fe₄N. 压力小于1 GPa时高压新相P2/m-Fe₄N 是热力学稳定的相, 且磁矩与γ’-Fe₄N的磁矩几乎相同. 2.9-19 GPa时, P2/m相的焓比γ’相的焓小, 基态结构更稳定. 大于20 GPa时, 两相磁矩几乎相同.     

High-pressure X-Ray diffraction and optical absorption studies of CsI

Static-compression data and absorption spectra for CsI have been collected to 61 GPa (610 kbar) at room temperature. The band gap closes with increasing pressure and CsI is expected to metallize at 105 (± 15) GPa. A second order phase transition to the CuAu I structure is observed at 39 (± 1) GPa. The elastic constants measured at low pressures do not predict that an elastic instability, and hence a structural distortion, would occur at elevated pressures. Similarly, an ionic pair-potential model which reproduces the properties of CsI at low pressures does not show the distortion to be stabilized at high pressures.     

Static strength of gold compressed up to 127 GPa

Gold powder is compressed non-hydrostatically up to 127 GPa in a diamond anvil cell(DAC),and its angle dispersive X-ray diffraction patterns are recorded.The compressive strength of gold is investigated in a framework of the lattice strain theory by the line shift analysis.The result shows that the compressive strength of gold increases continuously with the pressure up to 106 GPa and reaches 2.8 GPa at the highest experimental pressure(127 GPa) achieved in our study.This result is in good agreement with our previous experimental result in a relevant pressure range.The compressive strength of gold may be the major source of the error in the equation-of-state measurement in various pressure environments.     

4.0 GPa压力下纯橄岩弹性纵波速度和衰减的实验研究

 应用超声波透射法和超声波频谱振幅比法、在4.0 GPa压力条件下、测量了弹性纵波通过纯橄岩的波速（v_P）和品质因子值（Q_P，用于表征衰减）随压力的变化，并分析了纯橄岩内部结构的变化对波速和衰减的影响。在实验压力范围内（≤4.0 GPa），随压力升高，纯橄岩的纵波速度逐渐增大：从7.6 km/s（0.4 GPa）逐渐增大至8.5 km/s（4.0 GPa），升高了11.8%，低压时的增大幅度大于高压时的增大幅度。纯橄岩的品质因子值呈两段式线性变化：从低压区间到高压区间品质因子值的增大幅度明显变小（0.4~2.4 GPa压力范围内Q_P增大了358.5%，2.4~4.0 GPa压力范围内Q_P仅升高了7.6%）。纯橄岩的品质因子从54（0.4 GPa）升高至266.4（4.0 GPa），增大幅度达393.3%。在相对低压（0.4~2.4 GPa）条件下，纵波通过纯橄岩的速度增大、衰减降低主要是由于样品内的孔隙和微裂纹大量闭合，岩石密度增大，纵波在通过样品内孔隙和裂缝时损失的机械能降低，因此纵波通过纯橄岩的能量增大（即衰减降低），波速升高；当围压较高（2.4~4.0 GPa）时，纯橄岩内大部分裂纹已经闭合，而且矿物颗粒边界接触紧密。岩石内部的裂纹和颗粒之间由于摩擦滑动而损失的能量也变少，所以在高压时纯橄岩的波速和衰减的变化幅度变缓，但波速仍呈线性增大，而品质因子值（衰减）随压力升高几乎趋于不变。     

Electrical conductivity of xenon at megabar pressures

The electrical transport properties of solid xenon were directly measured at pressures up to 155 GPa and temperatures from 300 K to 27 mK. The temperature dependence of resistance changed from semiconducting to metallic at pressures between 121 and 138 GPa, revealing direct proof of metallization of a rare-gas solid by electrical transport measurements. Anomalies in the conductivity are observed at low temperatures in the vicinity of the transition such that purely metallic behavior is observed only at 155 GPa over the entire temperature range.     

Bonding in the superionic phase of water

The predicted superionic phase of water is investigated via ab initio molecular dynamics at densities of 2.0--3.0 g/cc (34-115 GPa) along the 2000 K isotherm. We find that extremely rapid (superionic) diffusion of protons occurs in a fluid phase at pressures between 34 and 58 GPa. A transition to a stable body-centered cubic O lattice with superionic proton conductivity is observed between 70 and 75 GPa, a much higher pressure than suggested in prior work. We find that all molecular species at pressures greater than 75 GPa are too short lived to be classified as bound states. Up to 95 GPa, we find a solid superionic phase characterized by covalent O-H bonding. Above 95 GPa, a transient network phase is found characterized by symmetric O-H hydrogen bonding with nearly 50% covalent character. In addition, we describe a metastable superionic phase with quenched O disorder.     

Osmium metal studied under high pressure and nonhydrostatic stress

Interest in osmium as an ultra-incompressible material and as an analog for the behavior of iron at high pressure has inspired recent studies of its mechanical properties. We have measured elastic and plastic deformation of Os metal at high pressures using in situ high pressure x-ray diffraction in the radial geometry. We show that Os has the highest yield strength observed for any pure metal, supporting up to 10 GPa at a pressure of 26 GPa. Furthermore, our data indicate changes in the nonhydrostatic apparent c/a ratio and clear lattice preferred orientation effects at pressures above 15 GPa.     

Optical microscopic,X-ray diffraction,and electrical resistance studies of CuCl at high pressure

Electrical resistance and X-ray diffraction measurements and also optical observations under a polarizing microscope were made on CuCl to pressures in excess of 12.5 GPa at room temperature using a diamond anvil cell. Resistance measurements were also performed in a piston-cylinder apparatus to pressures of approximately 5.5 GPa at room temperature. Three samples of CuCl prepared by different methods were examined. No anomalous pressure dependence in electrical resistance was found in the pressure range studied, and no dramatic changes in optical transmission were observed up to pressures of approximately 10.0 GPa. Optical observations and X-ray diffraction measurements indicate the existence of four phases in the pressure range studied, including a nonconducting black opaque phase which grows with time when CuCl is left for several days at the highest pressures.     

Understanding of the phase transformation from fullerite to amorphous carbon at the microscopic level

We study the shock-induced phase transformation from fullerite to a dense amorphous carbon phase by tight-binding molecular dynamics. For increasing hydrostatic pressures P, the C60 cages are found to polymerize at P<10 GPa, to break at P approximately 40 GPa, and to slowly collapse further at P>40 GPa. By contrast, in the presence of additional shear stresses, the cages are destroyed at much lower pressures (P<30 GPa). We explain this fact in terms of a continuum model, the snap-through instability of a spherical shell. Surprisingly, the relaxed high-density structures display no intermediate-range order.     

Unexpected behaviour of YbCu4.5 at very high pressures

We report resistivity measurements of the heavy fermion compound YbCu_4.5 for pressures up to 23.5 GPa. Although the temperature dependence of the resistivity in general does not change compared to previous results at lower pressures, surprisingly the temperature of the Kondo resistivity maximum increases with pressure at pressures exceeding 12.5 GPa. At the highest pressure of 23.5 GPa the resistivity was measured down to 50 mK. No trace of magnetic order, i.e. any anomaly in the resistivity behaviour has been found at this highest pressure reached.     

溴仿在冲击压缩下的光辐射及化学反应

 利用多通道光学高温计测量了溴仿在37 GPa到85 GPa压力范围内的温度,并观察了溴仿/单晶氯化钠界面的热驰豫过程。结果发现,当冲击波压力升高到46 GPa时,溴仿的光辐射强度随时间的变化呈现出“双阶梯”或“双台阶”形状的剖面结构,且台阶之间的时间间隔随冲击压力的增高而减小。当压力达到85 GPa时,上述“双台阶”结构消失,呈现为普通的单台阶剖面结构。冲击波温度测量表明,当压力低于50 GPa时,实测温度与Gokulya报道的数据一致;当压力增至76 GPa以上时,冲击波温度出现突跃性增加。结合对溴仿/氯化钠界面上的热驰豫过程的分析,文中提出,溴仿在上述冲击压力区间内发生了一次带有时间驰豫（或化学诱导期）的化学放热反应。     

Static EOS of uranium to 100 GPa pressure

Abstract

The crystal structure and compressibility of uranium has been determined by energy dispersive X-ray measurements in a diamond-cell apparatus up to pressures of 100 GPa. The alpha phase of uranium remains stable up to the highest pressures as suggested by earlier shock-Hugoniot data. An equation-of-state for alpha-uranium derived from both types of data implies that this phase also remains stable up to 2500 K at Hugoniot pressures of 100 GPa.     

1.0～4.4GPa下奥长石拉曼光谱特征的变化

常温、1.0～4.4GPa下,利用激光拉曼光谱研究了奥长石晶体结构随压力的变化。发现,压力为2.9GPa时,517cm-1附近出现新的谱峰,奥长石开始相变。3.4GPa时,源于奥长石结构中M—O伸缩振动的288cm-1拉曼谱峰频移发生突变,517cm-1附近谱峰消失,奥长石由三斜晶系完全相变为单斜晶系(P1-I1)。随压力增加,归属于奥长石四面体结构中Si—O—Si弯曲振动的458及516cm-1谱峰随压力增加有规律地向高频方向偏移,斜率分别是1.667cm-1/GPa和3.560cm-1/GPa,而源于Al—O—Al弯曲振动的480cm-1谱峰与压力没有明显的线性变化关系。卸压过程中,288cm-1拉曼谱峰频移保持不变,458,480及516cm-1谱峰向低频偏移。长石类矿物的相变压力与结构中八元环所含阳离子种类有关。     

The structure of liquid SnTe under pressure

We investigated the structure of liquid SnTe at high pressures up to 8.2 GPa by energy-dispersive x-ray diffraction. On melting at low pressures, the crystalline B1 structure changed into not B1-like but distorted-B1-like local structure. We also found that the structure changes at around 1.6-3.3 GPa. At high pressures, the bond angle and coordination number approached those for B2-based structure, but still showed clear deviations from B2-like local structure.     

罗丹明101的高压荧光特性

 测定了粉末罗丹明101（Rhodamine 101）及其在溶剂（甲醇、乙醇、水的混合液）中的高压荧光光谱。结果表明,粉末样品和溶液样品在高压下的发光性质有很大的区别。对于粉末样品,随着压力的增加,Rhodamine 101的荧光强度下降很快,在大约8 GPa时荧光峰几乎消失;伴随着荧光强度的变化,荧光峰峰位发生了显著红移（8 GPa内红移了近100 nm）。对于溶液样品,其荧光强度随压力的增加降低较慢,到13 GPa时,强度约为常压的10%,荧光峰峰位红移较小（13 GPa内红移约50 nm）。在压力作用下,Rhodamine 101分子结构的变化和特殊的溶剂效应,分别是影响其在粉末状态和溶液中荧光性质的主要因素。     

冲击压缩下金属的电导率测量

 探索了一种在兆巴压力冲击压缩下测量金属电导率的新方法——四电极垂向引线法，并用刻槽单晶蓝宝石作绝缘腔体，以消除分流效应对测量结果的影响。用二级轻气炮作为加载手段，测量了铁在终态平衡压力为101～208 GPa压力区间内的电导率（电导率从1.45×10⁶ S/m变化到7.65×10⁵ S/m）。将测量铁电导率的压力范围扩展到了200 GPa以上。实验结果表明，关于金属电导率的Bloch-Grüneisen公式在高达200 GPa冲击压力下仍然有效（对于ε-铁）。     

Dynamics of the BiTeI lattice at high pressures

Raman measurements of the phonon spectrum of BiTeI at pressures of up to 20 GPa have been performed. A decrease in the linewidth of E² vibration by almost a factor of 2 with an increase in the pressure to 3 GPa has been detected. The frequencies of all four Raman active modes increase monotonically with the pressure. These lines are observed in spectra up to ～8 GPa. Sharp change in the spectrum occurs at pressures of 8–9 GPa, indicating a transition to the high-pressure phase, which holds up to 20 GPa. This transition is reversible and hardly has any hysteresis. A sample in the high-pressure phase is single crystal.