金刚石压腔高温高压原位谱学研究的评述

金刚石压腔 (DAC)已经可以达到 5 5 0 GPa的压力和 6 0 0 0 K的温度 ,其高温高压谱学原位测量已经成为现代科学的一种重要的手段和方法。目前利用 DAC可以进行光谱学 (拉曼光谱、红外光谱、荧光光谱 )、衍射 (X射线衍射和 XAFS)、布里渊散射、核磁共振 (NMR)以及穆斯堡尔谱的高温高压原位研究。设计用于各种不同需要的便宜的压腔、合适的谱学测量方法以及压力内标物质是进一步拓宽 DAC应用的发展方向。     

New anvil designs in diamond-cells

New diamond anvils with conical support are introduced. Compared to conventional anvils the new design offers superior alignment stability, larger aperture, and reduced cost owing to significantly smaller anvil diameters. Except for table and culet, all surfaces are precision ground on a lathe, which lowers cost compared to faceted anvils. The conical design allows for steel supports, which are significantly easier and cheaper to manufacture than tungsten carbide supports. Conical support also prevents seat damage upon diamond failure. An additional new feature of the anvils is the roughened outer portion of the culet, which increases friction between the anvils and the gasket. This increases the height to diameter ratio of the pressure cell and prevents bonding between gasket and diamond, which causes ring cracks during pressure release. This technique replaces complicated diamond coating procedures. The anvils have been extensively tested for culets ranging from 0.1 to 1 mm diameter up to megabar pressures. A new anvil shape with cup-shaped culets to further increase the cell volume and gasket stability is also introduced.     

Neutron diffraction experiments in diamond and sapphire anvil cells

Diamond anvil cells (DAC) provide the highest static pressures ≥1?Mbar. Because of the low intensity of neutron sources, for a long time it was thought impossible to use DAC or other anvil cells in neutron experiments. We describe pressure cells with diamond and sapphire anvils and neutron instrumentation allowing neutron diffraction experiments to be carried out under pressures as high as 50?GPa, temperatures down to 0.1?K, and applied magnetic fields up to 7.5?T.     

High pressure studies using two-stage diamond micro-anvils grown by chemical vapor deposition

Ultra-high static pressures have been achieved in the laboratory using a two-stage micro-ball nanodiamond anvils as well as a two-stage micro-paired diamond anvils machined using a focused ion-beam system. The two-stage diamond anvils’ designs implemented thus far suffer from a limitation of one diamond anvil sliding past another anvil at extreme conditions. We describe a new method of fabricating two-stage diamond micro-anvils using a tungsten mask on a standard diamond anvil followed by microwave plasma chemical vapor deposition (CVD) homoepitaxial diamond growth. A prototype two-stage diamond anvil with 300?µm culet and with a CVD diamond second stage of 50?µm in diameter was fabricated. We have carried out preliminary high pressure X-ray diffraction studies on a sample of rare-earth metal lutetium sample with a copper pressure standard to 86?GPa. The micro-anvil grown by CVD remained intact during indentation of gasket as well as on decompression from the highest pressure of 86?GPa.     

金刚石压砧内单轴应力场对物质状态方程测量的影响

金刚石压砧的几何结构使得在高压下封垫内的样品通常处于单轴应力场中：压砧轴向加载应力最大,径向应力最小.由于金刚石压砧内非静水压单轴应力场的影响,用传统的高压原位X射线衍射方法测得的物质压缩曲线一般位于理想静水压压缩曲线之上.利用金刚石压砧径向X射线衍射技术以及晶格应变理论,结合最近的钨、金刚石和硼六氧样品的高压原位同步辐射径向X射线衍射实验结果,从宏观差应力、样品强度、标压物质和待测物质强度的关系三个方面分析讨论了金刚石压砧内单轴应力场对物质状态方程测量的影响及解决方案. 关键词： 金刚石压砧 单轴应力场 高压原位X射线衍射 状态方程     

Numerical optimization of diamond anvil cell design

Abstract

The procedure is presented for numerical optimization of geometrical parameters of a diamond anvil cell (DAC) and of loading conditions of DAC anvils. The calculation results are given which permit to increase the attainable pressure level more than 2,5-fold as compared with designs known from literature.     

Exploiting optical properties of nanopolycrystalline diamond in high pressure experiments

ABSTRACT

We investigated the optical properties (absorption, luminescence and Raman spectra) of nanopolycrystalline diamond (NPD) aiming at exploring its capabilities as a pressure sensor and as a pressure-cell anvil for combined X-ray/neutron and optical studies. Notably, we analysed the Raman peak shift and broadening with pressure using a Moissanite Anvil Cell (MAC). The results are compared with those obtained in a DAC, where Raman signals from NPD chips and diamond anvils strongly overlap. Its pressure behaviour in the hydrostatic and non-hydrostatic regimes were investigated. We showed that the nanopolycrystalline structure induces remarkable differences in the peak shift and broadening between NPD and natural type IIa single-crystal diamond, making NPD suitable as pressure gauge for pressure determination and testing hydrostaticity of pressure transmitting medium.     

The numerical modelling of the stress-strained state of diamond anvil cell components

Abstract

The method of numerical modelling of the behaviour of main components (anvils and deformable gasket) in diamond anvil cells (DAC) in the process of pressure generation has been developed and realized in the form of programs packages. The optimization of the geometry and loading conditions for an anvil was conducted in line with the multilevel factor plan of major effects (MFPME). A combination of optimizing factors allowing to obtain the theoretically predicted pressure of 465 GPa has been found, the value that by 2.7 times higher than that obtained on anvils at an analogous external pressure distribution [1] and the same diamond strength.

FEM     

Review: high pressure generation techniques beyond the limit of conventional diamond anvils

ABSTRACT

Current anvil designs and problems associated with various efforts to generate static high pressures beyond the limit of conventional diamond anvil cells (DACs) (～400?GPa) are reviewed. Pressures of up to 1?TPa have been reported by one research group using the double-stage DAC (ds-DAC) technique, but no other research group has successfully reproduced this high pressure result. Some research groups have used toroidal anvils, achieving pressures of >400?GPa. We have conducted numerous ds-DAC experiments and investigated the problems associated with such experiments. They include problems associated with various pressure scales in the multi-megabar region, difficulties in obtaining reliable X-ray diffraction patterns from micron-sized samples, and physical property measurements of tiny materials that may be harder than diamond. Each of these problems is discussed, following the summary of various experiments.     

Applications of nano-polycrystalline diamond anvils to X-ray absorption spectroscopy under high pressure

ABSTRACT

Recently, nano-polycrystalline diamond (NPD) anvils have been widely applied in high pressure research using X-ray absorption spectroscopy (XAS). The nanometer-sized polycrystallization in NPD anvils enables us to obtain glitch-free X-ray absorption spectra. This advantage of NPD anvils drastically improves the experimental conditions of XAS, which has previously used conventional single-crystal diamond (SCD) anvils. Distorted spectra due to the glitches from the SCD anvils have been an inevitable problem of XAS. This paper reviews recent studies of XAS and related spectroscopic techniques using the NPD anvils, which have mainly been performed on BL39XU of SPring-8. We demonstrate how NPD anvils are useful when using XAS for high pressure research.     

Melting curve of silicon to 15 GPa determined by two-dimensional angle-dispersive diffraction using a Kawai-type apparatus with X-ray transparent sintered diamond anvils

The melting curve of silicon has been determined up to 15 GPa using a miniaturized Kawai-type apparatus with second-stage cubic anvils made of X-ray transparent sintered diamond. Our results are in good agreement with the melting curve determined by electrical resistivity measurements [V.V. Brazhkin, A.G. Lyapin, S.V. Popova, R.N. Voloshin, Nonequilibrium phase transitions and amorphization in Si, Si/GaAs, Ge, and Ge/GaSb at the decompression of high-pressure phases, Phys. Rev. B 51 (1995) 7549] up to the phase I (diamond structure)—phase II (β-tin structure)—liquid triple point. The triple point of phase XI (orthorhombic, Imma)—phase V (simple hexagonal)—liquid has been constrained to be at 14.4(4) GPa and 1010(5) K. These results demonstrate that the combination of X-ray transparent anvils and monochromatic diffraction with area detectors offers a reliable technique to detect melting at high pressures in the multianvil press.     

High-pressure and high-temperature generation using diamond/sic composite anvils prepared with hot isostatic pressing

Using a hot isostatic pressing (HIP) technique, we synthesized diamond/SiC composites from diamond and Si powders. At an HIP condition of 1450 °C and 100 MPa, a pressure much lower than that of the diamond stability field, diamond powders react with molten Si to form well-sintered diamond/SiC composites. Cubes of the composites with 15 mm edge length were thereby fabricated, and an application to the second stage anvils in a Kawai-type high-pressure apparatus was attempted. A hybrid anvils system using four cubes of the composites and four of the conventional WC was introduced and heating experiments up to 1600 °C became possible. Because the diamond/SiC composites are transparent to X-rays, the present system is applicable not only to diffraction studies but also to radiographic studies that need a larger window for an X-ray image.     

A confocal set‐up for micro‐XRF and XAFS experiments using diamond‐anvil cells

A confocal set‐up is presented that improves micro‐XRF and XAFS experiments with high‐pressure diamond‐anvil cells (DACs). In this experiment a probing volume is defined by the focus of the incoming synchrotron radiation beam and that of a polycapillary X‐ray half‐lens with a very long working distance, which is placed in front of the fluorescence detector. This set‐up enhances the quality of the fluorescence and XAFS spectra, and thus the sensitivity for detecting elements at low concentrations. It efficiently suppresses signal from outside the sample chamber, which stems from elastic and inelastic scattering of the incoming beam by the diamond anvils as well as from excitation of fluorescence from the body of the DAC.     

Diamond anvil microcell

Abstract

A microminiature cryogenic diamond anvil cell (DAC) of overall dimensions ø10x24 mm made of nonmagnetic steel is described. A new principle allows to align anvils as perfectly as in traditional DACs. The microcell has been tested to 110 GPa.     

On-line laser heating setup for ED-XAS at ID24: preliminary optical design and test results

Double-sided laser heating (LH) combined with synchrotron X-ray radiation for in situ studies in the diamond anvil cell (DAC) has been the most productive and widely used high-temperature–high pressure technique in the past two decades. In the framework of the UPBL11 project (upgrade of ID24 beamline of European Synchrotron Radiation Facility), we developed a new on-line LH system for DACs. The preliminary optical scheme of the system is presented and discussed. Varying the settings, we are able to shape and to size the beam on the surface of the sample in the DAC. First pilot applications to the Fe case are shown.     

Optimization of Paris–Edinburgh press cell assemblies for in situ monochromatic X-ray diffraction and X-ray absorption

We describe some important improvements allowed by the development of new cell assemblies coupled to opposed conical sintered diamond anvils in the Paris–Edinburgh press. We provide X-ray absorption and diffraction experiments carried out at pressures up to 16.5 GPa. The maximum temperature reached was 1800 K for P<10 GPa and 1300 K for higher pressures. The sintered diamond anvils are X-ray transparent and give access to a much larger X-ray window than the tungsten carbide anvils, even at the highest pressure. Therefore, X-ray measurements are performed using in situ cross-calibration simultaneously. We also describe a new heating setup used to reach high temperatures, despite the low conductivity of the sintered diamond core by deviating the electrical current using copper strips. These improvements are illustrated by recent data collected using angle dispersive in situ X-ray diffraction on liquid Fe-18%wt S and using EXAFS at the barium K-edge on Ba₈Si₄₆ silicon clathrates and at the iodine K-edge on iodine-intercalated nanotubes.     

Development of a technique for high pressure neutron diffraction at 40 GPa with a Paris-Edinburgh press

ABSTRACT

We have developed a technique for neutron diffraction experiments at pressures up to 40?GPa using a Paris-Edinburgh press at the PLANET beamline in J-PARC. To increase the maximum accessible pressure, the diameter of the dimple for sample chamber at the top of the sintered diamond anvils is sequentially reduced from 4.0?mm to 1.0?mm. As a result, the maximum pressure increased and finally reached 40?GPa. By combining this technique with the beam optics which defines the gauge volume, diffraction patterns sufficient for full-structure refinements are obtainable at such pressures.     

Pressurizing conditions in helium-pressure-transmitting medium

We present quantitative measurements of the macroscopic non-hydrostatic stress and of the microscopic stress in samples compressed in a diamond anvil cell, using helium as a pressure-transmitting medium. These are based on the analysis of X-ray diffraction line shifts and widths. The macroscopic non-hydrostatic stress reaches 0.3–0.5 GPa at 150 GPa when the sample remains embedded in the pressure medium. The effect of this non-hydrostatic stress on the measured equations of state is estimated in the cases of gold, silver, molybdenum and copper. It is found to be negligible, except in the case of gold. We show that the analysis of the X-ray diffraction line shifts is a more sensitive way of detecting non-hydrostatic compression than the monitoring of the ruby luminescence signal. It can be used to detect when the sample is directly compressed between the diamond anvils. The sample geometry, in particular its thickness, has to be carefully chosen to prevent that situation.     

Conference summary on the first international workshop on advanced superhard materials

Composite diamond anvils have been developed for high-pressure/high-temperature measurements of diamond anvil cells. The anvils are fabricated using single-crystal chemical vapor deposition (CVD) from previously used and/or slightly damaged anvils made of natural or synthetic diamond. These composite anvils can be fabricated to possess optical characteristics at least comparable to conventional diamond anvils, whereas the single-crystal CVD portion is more durable because of its enhanced toughness relative to natural diamond. The viability of such anvils is demonstrated in measurements on hydrogen at megabar pressures and high temperature.     

氮化碳的高压同步辐射研究

 采用金刚石对顶砧及原位同步辐射实验技术,对高温高压有机催化反应制备的氮化碳材料,进行了室温及直到44 GPa压力条件下的原位高压同步辐射X射线衍射研究,并用最小二乘法拟合了样品的Murnaghan型等温状态方程。结果表明,在室温及直到44 GPa压力条件下,石墨相C₃N₄和待定的正交相CN材料都是稳定的,没有发生明显的相变,推测正交相CN材料可能是原始材料三聚氰胺和三聚氰氯在高温高压条件下催化热解产生的某种高分子有机聚合物。