Resistively heated,high pressure,membrane and screw driven diamond anvil cell

ABSTRACT

High temperature is of paramount importance in high pressure science. One of the leading tools in this respect is the resistively heated diamond anvil cell (DAC), where the heat is provided by small heaters, positioned close to the diamond/gasket/sample region (internally heated DAC, IHDAC) or by wrapping the DAC body into bigger heaters (externally heated DAC, EHDAC). Although IHDACs can reach sample temperatures higher than 1000?K, they are difficult to handle and the heater/diamond/gasket/sample region may be affected by strong thermal gradients potentially hindering accurate temperature measurements. Here we present a novel EHDAC, which overcomes these issues by uniquely joining: (i) high mechanical precision for multi-Mbar, (ii) high temperature alloys for operating to 1000?K, (iii) membrane or screw driven, easily switchable between each other, (iv) operation into a vacuum chamber, (v) uniform temperature, (vi) facile handling, and (vii) possibility to add internal heaters for achieving even higher temperatures.     

Nonmetallic gasket and miniature plastic turnbuckle diamond anvil cell for pulsed magnetic field studies at cryogenic temperatures

A plastic turnbuckle diamond anvil cell (DAC) and a nonmetallic gasket have been developed for pulsed magnetic field studies to address issues of eddy current heating and Lorentz forces in metal cells. The plastic cell evolved from our Ø 6.3 mm metal turnbuckle DAC that was designed in 1993 to rotate in the 9 mm sample space of Quantum Design's MPMS. Attempts to use this metal DAC in pulsed magnetic fields caused the sample temperature to rise to T>70 K, necessitating the construction of a nonconductive cell and gasket. Pressures of 3 GPa have been produced in the plastic cell with 0.8 mm culets in an optical study conducted at T=4 K. Variations of the cell are now being used for fermiology studies of metallic systems in pulsed magnetic fields that have required the development of a rotator and a special He-3 cryostat which are also discussed.     

Finite-element modeling of stresses and strains in a diamond anvil cell device: case of a diamond-coated rhenium gasket

The stresses and strains in a diamond anvil cell device were investigated using a finite-element code NIKE2D for the case of an ultra-hard composite gasket material. The pressure distribution in a diamond-coated rhenium gasket was measured by the energy dispersive diffraction technique to 213 GPa and compared with the finite-element modeling results. We examine various models for the mechanical properties of diamond-coated rhenium gasket as well as for diamond failure for shear stresses exceeding 100 GPa. The elastic and plastic properties of gasket were varied such that a good agreement between the experimentally measured pressure distribution and the computational pressure profiles were obtained. As a result, we obtained the effective Young’s modulus, Poisson’s ratio, yield stress for indented gasket, linear hardening modulus, and hardening parameter value for this layered ultra-hard composite gasket material. Future diamond design strategies for attainment of extreme high pressures using ultra-hard gasket materials are also discussed.     

An opposed-anvil-type apparatus with an optical window and a wide-angle aperture for neutron diffraction

We designed new anvil assemblies for acquiring high-quality neutron diffraction data and ruby fluorescence spectra inside a sample chamber. The conical aperture of Ni-binded WC anvils was expanded by a factor of two. A hybrid gasket made of TiZr- and Al-alloy was developed to prevent outward extrusion. A small and optically transparent window of moissanite was introduced to allow for the determination of pressure and hydrostaticity by measurement of ruby fluorescence spectra. High pressure-generation tests that make use of Bi electrical conductivity and ruby pressure markers revealed that pressure could be determined over 10 GPa. In situ synchrotron X-ray diffraction experiments were also carried out using NaCl as the pressure calibrants. The maximum pressure achieved was approximately 13 GPa. The neutron diffraction intensity from the newly generated anvil assemblies was 2.5–3.0 times greater than that using the standard toroidal anvil assemblies used previously.     

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.     

Conducting boron-doped single-crystal diamond films for high pressure research

Epitaxial boron-doped diamond films were grown by microwave plasma chemical vapor deposition for application as heating elements in high pressure diamond anvil cell devices. To a mixture of hydrogen, methane and oxygen, diborane concentrations of 240–1200 parts per million were added to prepare five diamond thin-film samples. Surface morphology has been observed to change depending on the amount of diborane added to the feed gas mixture. Single-crystal diamond film with a lowest room temperature resistivity of 18 mΩ cm was fabricated and temperature variation of resistivity was studied to a low temperature of 12 K. The observed minima in resistivity values with temperature for these samples have been attributed to a change in conduction mechanism from band conduction to hopping conduction. We also present a novel fabrication methodology for monocrystalline electrically conducting channels in diamond and present preliminary heating data with a boron-doped designer diamond anvil to 620 K at ambient pressure.     

Amorphous boron composite gaskets for in situ high-pressure and high-temperature studies

The diamond anvil cell (DAC) is a fundamental device used to explore the properties of materials under extreme pressure and temperature (P/T) conditions. In the past years, simultaneous high P/T DAC experiments using the resistively heated DAC (RH-DAC) techniques have been developed for studying materials properties in a wide P/T range. However, the mechanical instability of metallic gaskets used for sample confinement at high P/T conditions remains a limiting factor for exploiting the accessible P/T range of the RH-DAC. In this study, we present a new gasket configuration that overcomes these limitations. It is based on an amorphous boron–epoxy mixture inserted in a rhenium gasket. We show how these gasket inserts stabilize the sample chamber over a wide P/T range, allowing monitoring sample properties using X-ray diffraction and absorption spectroscopy up to 50?GPa and 1620?K.     

Measurement of improved pressure dependence of superconducting transition temperature

We describe a technique for making electrical transport measurements in a diamond anvil cell at liquid helium temperature having in situ pressure measurement option, permitting accurate pressure determination at any low temperature during the resistance measurement scan. In general, for four-probe resistivity measurements on a polycrystalline sample, four fine gold wires are kept in contact with the sample with the help of the compression from the soft solid (usually alkali halides such as NaCl, KCl, etc.) acting as a pressure-transmitting medium. The actual pressure on the sample is underestimated if not measured from a ruby sphere placed adjacent to the sample and at that very low temperature. Here, we demonstrate the technique with a quasi-four-probe resistance measurement on an Fe-based superconductor in the temperature range 1.2–300 K and pressures up to 8 GPa to find an improved pressure dependence of the superconducting transition temperature.     

Pressure measurement using the R fluorescence peaks and 417 cm−1 Raman peak of an anvil in a sapphire-anvil cell

In this study, synthetic sapphire crystals were used as anvils, coupled with a metal gasket, in a Merrill–Bassett-type pressure cell (sapphire-anvil cell (SAC)). Quartz and ruby chips were compressed in the cell and used as pressure calibrators for the SAC. In the sample–anvil interface, the relationship of the frequency shifts of the R1, R2 and 417 cm^?1 peaks with pressure was studied. They were constructed as new pressure calibrators. To test the applicability of the newly calibrated SAC, the Raman spectra of dolomite and calcite were measured in situ at room temperature.     

Hybrid Bridgman anvil design: an optical window for in situ spectroscopy in large volume presses

The absence of in situ optical probes for large volume presses (LVPs) often limits their application to high-pressure materials research. In this article, we present a unique anvil/optical window design for use in LVPs, which consists of an inverted diamond anvil seated in a Bridgman-type anvil. A small cylindrical aperture through the Bridgman anvil ending at the back of diamond anvil allows optical access to the sample chamber and permits direct optical spectroscopy measurements, such as ruby fluorescence (in situ pressure) or Raman spectroscopy. The performance of this anvil design has been demonstrated by loading KBr to a pressure of 14.5 GPa.     

Simultaneous electrical and X-ray diffraction studies on neodymium metal to 152 GPa

Using designer diamond anvils and angle dispersive X-ray diffraction technique at a synchrotron source, we have performed simultaneous electrical and structural studies on neodymium metal to 152 GPa in a diamond anvil cell. Four-probe electrical resistance measurement shows a 38% decrease in the electrical resistivity, associated with the delocalization of the 4f-shell electrons, starting at 100 GPa up to a final pressure of 152 GPa. The continuous decrease in electrical resistivity is consistent with the observation of a gradual phase transition to α-U structure in this pressure range. The (1 1 1) diffraction peak of α-U structure first appears at 100 GPa and increases in intensity with increasing pressure to 152 GPa. This increase in intensity is attributed to an increasing volume fraction of α-U phase and an increase in structural y-parameter from 0.07 at 118 GPa to 0.095 at 152 GPa. In contrast to the abrupt pressure-induced f-electron transition seen in cerium and praseodymium, the continuous evolution of α-U structure and electrical resistivity in neodymium confirms the gradual nature of 4f delocalization process in this element.     

一种以压力一维均匀分布为特征的长条形对顶压砧

针对圆形端面平面对顶压砧装置中压力梯度大的问题, 本文设计了一种长条形端面的平面对顶压砧, 相应的封垫也改为长条形. 原理分析表明: 这种压砧可在沿长条形中心线的狭长区域内产生均匀分布的高压力. 本文采用长20 mm宽5 mm长条形端面的硬质合金压砧配合叶腊石封垫进行压力标定, 实验结果显示: 这种装置可产生10 GPa以上的高压, 在长条形中心线上至少12 mm长度范围内的不同位置上产生的压力基本一致, 在2.55 GPa压力时测量偏差小于2.0%, 在7.7 GPa时测量偏差小于3.6%. 这种特点很有利于对细长样品进行精确的高压物性测量.     

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.     

Magnetic ordering temperatures in rare earth metal dysprosium under ultrahigh pressures

Magnetic ordering temperatures in heavy rare earth metal dysprosium (Dy) have been studied using an ultrasensitive electrical transport measurement technique in a designer diamond anvil cell to a pressure of 69 GPa and a temperature of 10 K. Previous studies using magnetic susceptibility measurements at high pressures were able to track magnetic ordering temperature only till 7 GPa in the hexagonal close packed (hcp) phase of Dy. Our studies indicate that the magnetic ordering temperature shows an abrupt drop of 80 K at the hcp-Sm phase transition followed by a gradual decrease that continues till 17 GPa. This is followed by a rapid increase in the magnetic ordering temperatures in the double hcp phase and finally leveling off in the distorted face centered cubic phase of Dy. Our studies reaffirm that 4f-shell remains localized in Dy and there is no loss of magnetic moment or 4f-shell delocalization for pressures up to 69 GPa.     

Methodology for in situ synchrotron X-ray studies in the laser-heated diamond anvil cell

ABSTRACT

A review of some important technical challenges related to in situ diamond anvil cell laser heating experimentation at synchrotron X-ray sources is presented. The problem of potential chemical reactions between the sample and the pressure medium or the carbon from the diamond anvils is illustrated in the case of elemental tantalum. Preliminary results of a comparison between reflective and refractive optics for high temperature measurements in the laser-heated diamond anvil cell are briefly discussed. Finally, the importance of the size and relative alignment of X-ray and laser beams for quantitative X-ray measurements is presented.     

High–pressure electrical conductivity and Raman spectroscopy of chalcanthite

Abstract

The phase transitions and dehydration of chalcanthite were investigated by electrical conductivity and Raman spectroscopy at 1.0–24.0?GPa and 293–673?K in a diamond anvil cell. At ambient temperature, two secondary phase transitions were observed according to discontinuous changes in the slope of Raman shifts, full width at half maximum and electrical conductivities at ～7.3 and ～10.3?GPa. The dehydration temperatures were determined by the splitting of Raman peaks and changes in electrical conductivity as ～350 and ～500?K at respective ～3.0 and ～6.0?GPa. A positive relationship for chalcanthite between dehydration temperature and pressure is established.     

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。     

Laser heating in diamond anvil cells: developments in pulsed and continuous techniques

Developments in continuous and pulsed laser‐heating techniques, and finite‐element calculations for diamond anvil cell experiments are reported. The methods involve the use of time‐resolved (5 ns gated) incandescent light temperature measurements to determine the time dependence of heat fluxes, while near‐IR incandescent light temperature measurements allow temperature measurements to as low as 500 K. Further optimization of timing in pulsed laser heating together with sample engineering will provide additional improvements in data collection in very high P–T experiments.     

Elastic and plastic deformation of NaCl and Ni3Al polycrystals during compression in a multi-anvil apparatus

Abstract

The compression behaviour in a multi-anvil apparatus of pure NaCl and of a foil of Ni₃Al embedded in a pressure medium of NaCl has been studied by energy-dispersive X-ray diffraction. At ambient temperature, the pressure and stresses, determined from line positions of NaCl, were constant throughout the sample chamber. Line positions and line widths of NaCl reflections were reversible on pressure release. A saturation of microstrains observed in NaCl at 2 GPa is thus attributed to brittle fracture setting in at uniaxial stresses of around 0.3 GPa. Ni₃Al polycrystals, in contrast, undergo extensive (ductile) plastic deformation above 4 GPa. The compression behaviour of both Ni₃Al and NaCl is identical to that previously determined in a diamond anvil cell. While a multi-anvil device thus has the advantage, compared with a diamond anvil cell, of constant pressure and stress throughout the sample chamber, microstrains in poly-crystalline samples arise in both devices. Samples in a multi-anvil apparatus thus need to be mixed with a pressure medium and to consist of essentially single crystals just as in a diamond anvil cell. Annealing experiments at high pressures confirm that the release of the uniaxial stress component in the pressure medium does not cause a release of microstrains in the embedded sample if the latter has been plastically deformed. Annealing for the purpose of attaining hydrostatic conditions in compression studies thus has to be carried out with care.