Deformation textures produced in diamond anvil experiments, analysed in radial diffraction geometry

Diamond anvil cells may not only impose pressure upon a sample but also a compressive stress that produces elastic and plastic deformation of polycrystalline samples. The plastic deformation may result in texture development if the material deforms by slip or mechanical twinning, or if grains have a non-equiaxed shape. In radial diffraction geometry, texture is revealed by variation of intensity along Debye rings relative to the compression direction. Diffraction images (obtained by CCD or image plate) can be used to extract quantitative texture information. Currently the most elegant and powerful method is a modified Rietveld technique as implemented in the software package MAUD. From texture data one can evaluate the homogeneity of strain in a diamond anvil cell, the strain magnitude and deformation mechanisms, the latter by comparing observed texture patterns with results from polycrystal plasticity simulations. Some examples such as olivine, magnesiowuestite, MgSiO(3) perovskite and ε-iron are discussed.     

Strength and elasticity of SiO2 across the stishovite-CaCl2-type structural phase boundary

Radial x-ray diffraction experiments were conducted under nonhydrostatic compression on SiO2 to 60 GPa in a diamond anvil cell. This ratio of differential stress to shear modulus t/G is 0.019(3)-0.037(5) at P=15-60 GPa. The ratio for octahedrally coordinated stishovite is lower by a factor of about 2 than observed in four-coordinated silicates. Using a theoretical model for the shear modulus, the differential stress of stishovite is found to be 4.5(1.5) GPa below 40 GPa and to decrease sharply as the stishovite-CaCl2-type phase transition boundary is approached. Inversion of measured lattice strains provides direct experimental evidence for softening of C11-C12.     

In situ conductivity measurement of matter under extreme conditions by film fabrication on diamond anvil cell

The film-fabricating technology has been used to prepare the microcircuit on diamond anvil for resistivity measurement under extreme conditions. We chose molybdenum as the electrode material and alumina as the insulator and protective material. The sample thickness measurement was conducted and then the resistivity correction was performed under different thickness. The experimental error was proved to be less than 10%. By mounting alumina film between diamond anvil and microcircuit, high-temperature performance of a laser heating diamond anvil cell was improved obviously, which is available for in situ resistivity measurement under high pressure and high temperature. Meanwhile, the impedance spectroscopy of a powdered semiconductor sample was detected. Through the impedance arcs obtained, the grain boundary contribution to the resistivity can be well distinguished.     

Simultaneous determination of mean pressure and deviatoric stress based on numerical tensor analysis: a case study for polycrystalline x-ray diffraction of gold enclosed in a methanol-ethanol mixture

It is known that the {100} and {111} planes of cubic crystals subjected to uniaxial deviatoric stress conditions have strain responses that are free from the effect of lattice preferred orientation. By utilizing this special character, one can unambiguously and simultaneously determine the mean pressure and deviatoric stress from polycrystalline diffraction data of the cubic sample. Here we introduce a numerical tensor calculation method based on the generalized Hooke's law to simultaneously determine the hydrostatic component of the stress (mean pressure) and deviatoric stress in the sample. The feasibility of this method has been tested by examining the experimental data of the Au pressure marker enclosed in a diamond anvil cell using a pressure medium of methanol-ethanol mixture. The results demonstrated that the magnitude of the deviatoric stress is ～0.07?GPa at the mean pressure of 10.5?GPa, which is consistent with previous results of Au strength under high pressure. Our results also showed that even a small deviatoric stress (～0.07?GPa) could yield a ～0.3?GPa mean pressure error at ～10?GPa.     

Stishovite and post-stishovite polymorphs of silica in the shergotty meteorite: their nature,petrographic settings versus theoretical predictions and relevance to Earth's mantle

The Shergotty meteorite contains three dense silica polymorphs in distinct petrographic settings: (1) two post-stishovite SiO₂ polymorphs in individual multiphase grains coexisting with glass with nearly labradorite composition, and (2) large individual stishovite grains in shock-melt pockets which also contain the new CAS phase (Calcium-aluminosilicate; CaAl₄Si₂O₁₁; [Phys Earth Planet Interiors 97 (1996) 97; Geophys Abstract 5(2003)] and hollandite structured plagioclase composition. Prismatic and wedge-shaped grains of the original accessory tridymite (or cristobalite) in the Shergotty meteorite were densified during a major impact event on the Shergottite–Nakhlite–Chaissingite (SNC) parent body and inverted either to (1) multiphase assemblages of several post-stishovite polymorphs depicting prominent tweed pattern or to (2) Large homogeneous stishovite grains in melt pockets. In the first setting we identified an orthorhombic and a monoclinic post-stishovite silica polymorph, respectively. TEM investigations of a grain containing the orthorhombic polymorph revealed an α-PbO₂ like phase that could be assigned to either Pnc2 (with the cell parameters: a=4.55±0.01 Å, b=4.16±0.03 Å, c=5.11±0,04 Å), or Pbcn space group and dense SiO₂ glass. The X-ray diffraction pattern from a second grain revealed a polymorph with a monoclinic lattice with the space group P21/c, that is related to the baddeleyite (ZrO₂) structure with the cell parameters: a=4.375(1) Å, b=4.584(1) Å, c=4.708(1) Å, β=99.97(3), ρ=4.30(2) g/cm³. TEM-SAED pattern of this grain revealed the presence of the α-PbO₂-like SiO₂ polymorph, stishovite, secondary cristobalite, and dense silica glass. The coexistence of several high-density polymorphs and dense silica glass in the same grain suggests that several post-stishovite phases were formed during the shock event in Shergotty. Some of these polymorphs were highly unstable and vitrified, presumably in the decompression stage. Based on diamond anvil experiments on cristobalite a peak shock pressure in excess of 40 GPa could be deduced. The petrographic setting and texture of the single stishovite grains in the melt pockets is different. The mono-phase individual grains occur exclusively as large (>10 μm) rounded objects inside melt pockets together with hollandite structured plagioclase composition and the new CAS phase [1]. Stishovite in melt pockets is barren of any sign of a tweed pattern and contains no silica glass. This suggests that the mechanisms of phase transitions were different in the two lithologies. Stishovite in the melt pockets probably did not form by a retrograde transformation from a post-stishovite polymorph.     

Anvil design for slip-free high pressure deformation experiments in a rotational diamond anvil cell

A rotational diamond anvil cell is the most suitable deformation apparatus with which to investigate the rheological properties of deep-Earth materials at pressures similar to those found in the lower mantle and core. However, slip between the sample and piston is still a problem, since the slip prevents the attainment of a constant strain rate and interferes with the uniform deformation of a sample. In this paper, we report that using a diamond anvil with deep grooves results in a marked improvement in the coupling between the sample and the diamond anvils.     

复合型多晶金刚石末级压砧的制备并标定六面顶压机6-8型压腔压力至35GPa

通过分析二级6-8型大腔体静高压装置八面体压腔的受力状况, 研制了一种使用成本低、尺寸大且易于加工的多晶金刚石-硬质合金复合二级(末级)顶锤(压砧). 采用原位电阻测量观测Zr在高压下相变(α-ω, 7.96 GPa; ω-β, 34.5 GPa)的方法, 标定了由多晶金刚石-硬质合金复合末级压砧构建的5.5/1.5(传压介质边长/二级顶锤锤面边长, 单位: mm)组装的腔体压力. 实验表明, 自行研制的多晶金刚石-硬质合金复合末级压砧可使基于国产六面顶压机构架的二级加压系统的压力产生上限从约20 GPa提高到35 GPa以上, 拓展了国内大腔体静高压技术的压力产生范围. 应用这一技术, 我们期望经过末级压砧材料与压腔设计的进一步优化, 在基于国产六面顶压机的二级6-8 型大腔体静高压装置压腔中产生超过50 GPa的高压. 关键词： 二级6-8型大腔体静高压装置 多晶金刚石-硬质合金复合末级压砧 压力标定     

Effect of deformation of diamond anvil and sample in diamond anvil cell on the thermal conductivity measurement

Studies show that the sample thickness is an important parameter in investigating the thermal transport properties of materials under high-temperature and high-pressure (HTHP) in the diamond anvil cell (DAC) device. However, it is an enormous challenge to measure the sample thickness accurately in the DAC under severe working conditions. In conventional methods, the influence of diamond anvil deformation on the measuring accuracy is ignored. For a high-temperature anvil, the mechanical state of the diamond anvil becomes complex and is different from that under the static condition. At high temperature, the deformation of anvil and sample would be aggravated. In the present study, the finite volume method is applied to simulate the heat transfer mechanism of stable heating DAC through coupling three radiative-conductive heat transfer mechanisms in a high-pressure environment. When the temperature field of the main components is known in DAC, the thermal stress field can be analyzed numerically by the finite element method. The obtained results show that the deformation of anvil will lead to the obvious radial gradient distribution of the sample thickness. If the top and bottom surfaces of the sample are approximated to be flat, it will be fatal to the study of the heat transport properties of the material. Therefore, we study the temperature distribution and thermal conductivity of the sample in the DAC by thermal-solid coupling method under high pressure and stable heating condition.     

静-动加载相结合的材料状态方程实验平台的研制

根据神光-Ⅱ第九路高功率激光加载的特点,对传统静高压金刚石压砧装置进行了改进和优化设计,研制出了适合高功率激光加载条件下材料宽域状态方程研究的新型静高压靶.在神光-Ⅱ高功率激光装置上建立了基于静高压金刚石压砧和动高压激光相结合的材料宽域状态方程研究平台.利用这一平台开展了超纯水的宽域状态方程实验探索,获得了较好的实验结果.     

0.1~3 000 MPa下碳化硅顶砧拉曼光谱作为压力计的研究

 利用Mao-Bell型水热金刚石压腔，以6H型碳化硅晶体作为顶砧，在常温下对碳化硅顶砧的不同点位进行拉曼光谱的原位测量，探讨了在一定条件下利用碳化硅顶砧的969拉曼峰位移作为压力标定的可行性、所具有的优点及需要改进的方面，并且得到了室温下的压力测量公式。     

低温下使用的金刚石对顶砧高压盒和显微光谱系统

自Bridgeman发明套筒活塞高压装置以来,特别是引入金刚石压砧后,高压物理学发展迅速。这种金刚石对顶砧压力盒,简称为DAC,为研究高压下材料的光学性质提供了极大的方便。为进行高压低温研究,目前国内都是将压机浸入液氮中,或向DAC喷浇液氮。这样只能在77K恒温,且必须取出压机后才能加压。     

石英拉曼峰进行压力标定的误差研究

在常温常压下进行了作为压标的石英颗粒的拉曼光谱测量和研究。研究结果发现,在25℃和常压条件下,不同的石英颗粒测得的Si—O振动模在463.59～464.65cm-1范围内变化,误差为(±0.1～±0.3)cm-1。其中不同石英颗粒拉曼峰的最大差异达1.06cm-1,远远大于其测量误差。我们认为这是由于石英破碎时使石英颗粒内产生的应力所致。因此,在进行金刚石压腔高温高压实验的压力确定时,必须以常压下实测的Si—O振动模测量值为零压参考点。另外,拉曼光谱仪的波数漂移以及环境温度的不稳定均会造成不可忽视的压力测量误差,应对此进行校正。     

High Pressure Instrumentation: Low and Negative Pressures

Much work on semiconductors, soft solids and biological materials does not require the megabar capability of the diamond anvil cell; a few accurate kbar being all that may be required. Work in this range poses its own challenges, to make the experiments routine, safe and reliable, and well-calibrated. We contrast diamond anvil cells working at what for them is very low pressure, with traditional bombs working at what for them is dangerously high pressure. We describe our preferred solution, a single-diamond cell, and demonstrate its use with Raman data from ethanol under low pressure. Negative hydrostatic pressure cannot be obtained by traditional methods. However, we present data showing the Raman spectrum of ethanol apparently at the negative pressure of m 3 kbar.     

Measuring grain rotation at the nanoscale

In this paper, we introduced a method to measure grain rotation of nanomaterials under external stress using a high pressure diamond anvil cell and the Laue microdiffraction technique at a synchrotron facility. We used tungsten carbide marker crystals to investigate grain rotation activities of 3 and 500?nm nickel media. Our results show that the grain rotation of 3 and 500?nm nickel nanocrystals increase with pressure and finally rotation of 500?nm nickel tends to stop at a lower pressure/stress level than 3?nm nickel. 3?nm nickel nanocrystals show a higher rotation magnitude than 500?nm nickel nanocrystals. Our measurements show an effective method to study the grain rotation of nanomaterials especially in ultrafine nanocrystals.     

苯甲酸脱羧反应过程的拉曼光谱研究

应用水热金刚石压腔结合拉曼光谱技术研究了升温过程中苯甲酸在水中的变化及拉曼谱图。结果表明：低温升温过程中,苯甲酸的拉曼谱图中各个特征振动谱峰没有变化,苯甲酸没有与水反应。随着温度的继续升高,苯甲酸的拉曼谱图中的特征振动峰逐渐变弱。升至150 ℃时,羧基的拉曼特征谱峰消失,说明此过程中苯甲酸发生了脱羧反应。继续升温至170 ℃,苯甲酸溶解消失。随后将体系降至常温,发现有晶体析出。由其拉曼谱图可知,重结晶的晶体含有苯环的特征峰,说明有芳香烃析出。但是没有测到羧基的特征拉曼谱峰,说明重结晶的晶体不是苯甲酸。整个过程可以说明,芳香烃在溶解重结晶过程中是可逆的,羧基是不可逆的。     

X-ray absorption spectroscopy under high pressures in diamond anvil cells

Abstract

Although potentially extremely important for understanding the high-pressure microscopic behaviour of materials, over the years the area of high-pressure EXAFS in particular using diamond anvil cells has proved to be technically difficult. This has significantly hampered its development. The interference of X-ray dimaction from the diamonds in the diamond anvil cell with the absorption signal has proved to be a challenging problem to tackle, restricting the use of high-pressure EXAFS to energies below about 11 key Below 11 keV however the technique is also limited due to absorption of incident X-rays by the diamonds making it virtually impossible to conduct X-ray absorption experiments below about 9keV In this paper we describe in detail the methodology for scanriirig high-pressure EXAFS in diamond anvil cells and examine the origins of the associated problems and ways of dealing with them. We also demonstrate that it is possible to extend the useful range of studied absorption edges from 7keV up to at least 30keV This brings about new opportunities for high pressure EXAFS using diamond anvil cells.     

Quantitative Rietveld texture analysis of CaSiO(3) perovskite deformed in a diamond anvil cell

The Rietveld method is used to extract quantitative texture information from a single synchrotron diffraction image of a CaSiO(3) perovskite sample deformed in axial compression in a diamond anvil cell. The image used for analysis was taken in radial geometry at 49?GPa and room temperature. We obtain a preferred orientation of {100} lattice planes oriented perpendicular to the compression direction and this is compatible with [Formula: see text] slip.     

高温高压下硬水铝石状态方程研究

 在金刚石压砧装置上,用氧化铝膜作绝热层,借助同步辐射和双面激光加温系统,分析了硬水铝石在高温高压下的结构变化,并分别用理论和实验的方法得出了其结构参数,得到了样品在不同压力温度下的体模量。这对于人们认识和研究地壳结构和地球内部物质的演化具有重要意义。研究发现,在常温和高温时其压缩率有明显不同,在高温高压范围内,其晶格常数和晶胞体积的变化非常接近样品在高压常温下的情况;而在高温低压范围内,情形和常温时有较大差别。在实验过程中并没有发现相变的产生。     

金刚石对顶砧中触点位置误差对样品电阻率测量精度的影响

利用有限元分析方法,研究了金刚石对顶砧中电极与样品接触点位置变化对范德堡法测量样品电阻率精度的影响.结果表明:当电极中心与样品边缘的间距b≤d/9(d为样品直径)时能得到精确的电阻率测量结果;当电极位置远离样品边缘而逐渐接近样品中心时,其位置变化对电阻率测量精度的影响迅速增大;相同的电极位置变化对具有较大电阻率的半导体样品电阻率测量精度的影响更明显. 关键词： 电阻率 有限元方法 金刚石对顶砧