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.     

Ruby fluorescence lifetime measurements for temperature determinations at high (p,T)

The lifetime of the ruby R₁ fluorescence line was measured as a function of pressure (up to about 20 GPa) and temperature (550 K) in an externally heated diamond anvil cell (DAC). At constant temperatures, the lifetime is increasing linearly with increasing pressure. The slope of the pressure dependence is constant up to a temperature of 450 K and it is decreasing at higher temperatures. At constant pressure, the lifetime is exponentially decreasing with increasing temperature. The (p, T)-dependence can be parametrized by the combination of a linear and an exponential function. This allows an accurate p, T-determination by the combination of fluorescence spectroscopy using Sm²⁺-doped strontium tetraborate and lifetime measurements of ruby, as the energy of the Sm²⁺ fluorescence is nearly temperature-independent.     

High pressure behavior of nano-crystalline CeO2 up to 35 GPa: a Raman investigation

The present paper reports the results of in situ Raman studies carried out on nano-crystalline CeO₂ up to a pressure of 35 GPa at room temperature. The material was characterized at ambient conditions using X-ray diffraction and Raman spectroscopy and was found to have a cubic structure. We observed the Raman peak at ambient at 465 cm^?1, which is characteristic of the cubic structure of the material. The sample was pressurized using a diamond anvil cell using ruby fluorescence as the pressure monitor, and the phase evolution was tracked by Raman spectroscopy. With an increase in the applied pressure, the cubic band was seen to steadily shift to higher wavenumbers. However, we observed the appearance of a number of new peaks around a pressure of about 34.7 GPa. CeO₂ was found to undergo a phase transition to an orthorhombic α -PbCl₂-type structure at this pressure. With the release of the applied pressure, the observed peaks steadily shift to lower wavenumbers. On decompression, the high pressure phase existed down to a total release of pressure.     

Structure refinement of sub-cubic-mm volume sample at high pressures by pulsed neutron powder diffraction: application to brucite in an opposed anvil cell

Neutron powder diffraction measurements of 0.9 mm³ of mixture of deuterated brucite and pressure medium were conducted at pressures to 2.8 GPa, using an opposed anvil cell and a medium-resolution diffractometer at Japan Proton Accelerator Research Complex pulsed neutron source. Spurious-free diffraction patterns were successfully obtained and refined to provide all structural parameters including Debye–Waller factors. Tilting of hydroxyl dipoles of brucite toward one of the three nearest-neighbor oxygen anions was confirmed to be substantial at pressure as low as 1.5 GPa. By this application, technical feasibility to analyze such a small sample has been newly established, which would be useful to extend the applications of neutron diffraction at high pressures.     

126.5 GPa准静水压下的光谱学实验

 本文介绍了作者利用国内加工的金刚石压砧装置及组建的微区光谱系统进行100 GPa（百万大气压）准静水压光谱学实验的概况，证明压力产生装置和微区光谱系统的多功能性是充分可靠的。实验中遇到的压力产生能力超过压力测量能力的事实，反映了高压光谱学实验在压力范围扩大时所遇到的挑战。文中对高压下的拉曼、发射、吸收及反射光谱的实验原理和实验方法也作了概略的介绍。     

A portable high-pressure stress cell based on the V7 Paris–Edinburgh apparatus

We describe a new device, based on a V7 Paris–Edinburgh press, for torsional testing of material at pressures up to 7 GPa (extendable to 15 GPa). Samples are deformed using a simple shear geometry between opposed anvils by rotating the lower anvil, via a rotational actuator, with respect to an upper, stationary, anvil. Use of conical anvil profiles greatly increases sample dimensions more than other high-pressure torsional apparatus did. Samples of polycrystalline Zr (2 mm thick, 3.5 mm diameter) have been sheared at strains exceeding γ ～1.5 at constant strain rate and at pressures from 1.8 to 5 GPa, and textural development has been studied by electron microscopy. Use of amorphous-boron-epoxy gaskets means that nearly simple shear of samples can be routinely achieved. This apparatus allows study of the plastic and anelastic behaviour of materials under high pressure, and is particularly suited for performing in situ investigations using synchrotron or neutron radiation.     

超高压下碘的结构相变

 采用DAC高压X光技术，在320 GPa压力下，对碘进行了结构相变的研究。用耐腐蚀材料Mo作封垫，在室温和无保护气氛下装样。采用Mo内标和红宝石荧光测量进行压力校准。结果表明，在21 GPa时，开始发生结构相变，由面心正交相（Ⅰ相），转变为体心正交相（Ⅱ相），体积缩小2%左右。在21~25 GPa之间为两相共存区；在25 GPa以上完全转变为新的高压单相（Ⅱ相）。此相变为可逆相变。     

X-ray studies of the semiconductors snas,InTe, TlS and TISe UP TO 43 GPa

Abstract

The structures of the semiconductors SnAs, InTe, TlS and TlSe have been investigated using high-pressure (HP) diffraction technique-a gasketed diamond anvil cell (DAC)'. The pressure was measured by ruby fluorescence technique. The first order reversible transition from NaCl to CsCl structure was found in SnAs with volume discontinuity 5% the two-phase area extends from 32 to 43 GPa. The volume change V/v,(P) of the SnAs is shown in Figure 1. In agreement with the gomology rule3, the same pressure effect has been found in Sn_xSb1?x atP=9 GPa2.     

Synthetic diamonds for multimegabar pressures in the diamond anvil cell

Abstract

Synthetic Type 1b yellow diamonds containing nitrogen in substitutional form and with extremely low birefringence were used as anvils for ultra high pressures in the diamond anvil cell. Pressures were measured by the ruby fluorescence technique to above 200 GPa. Using x-ray diffraction the maximum pressure was 210 GPa, while an x-ray based pressure of 245 GPa was achieved with natural diamonds with a somewhat more optimal geometry. Nitrogen platelets appear to be not essential for exceeding 200 GPa. The optical properties of synthetic diamond at ambient and megabar stresses will be discussed.     

Pulsed neutron powder diffraction at high pressure by a capacity-increased sapphire anvil cell

A new design of opposed anvil cell for time-of-flight neutron powder diffraction was prepared for use at advanced pulsed sources. A couple of single-crystal sapphire sphere anvils and a gasket of fully hardened Ti–Zr null alloy were combined to compress 35 mm³ of sample volume to 1 GPa and 11 mm³ to 2 GPa of pressures, respectively. A very high-quality powder diffraction pattern was obtained at Japan Proton Accelerator Research Complex for a controversial high pressure phase of methane hydrate. The counting statistics, resolution, absolute accuracy and d-value range of the pattern were all improved to be best suitable for precise structure refinement. The sample is optically accessible to be measured by Raman and fluorescence spectroscopy during and after compression. The current cell will be an alternative choice to study hydrogenous materials of complex structures that are stable at the described pressure regime.     

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.     

Compression behavior of NiO in a diamond cell

Abstract

The compressibility of synthetic polycrystalline NiO was studied in a diamond anvil cell at room temperature utilizing two different X-ray sources. A standard film with a conventional X-ray source and the energy dispersive X-ray diffraction (EDXRD) method with synchrotron radiation were used for data acquisition. In the film method, the sample was compressed in a 4:1 methanol to ethanol solution up to 7 GPa with ruby fluorescence as a pressure calibrant. In the energy dispersive method, NiO powder was mixed with gold and compressed in two different conditions: gasketed and ungasketed up to 30 GPa. In the gasketed run, water was used as the pressure transmitting medium while gold was used as pressure calibrant in both runs.

Hydrostatic compression of NiO in both diffraction methods yields a bulk modulus (K _o) of 187 ± 7 GPa assuming K′ = 4. The compression of gasketed NiO of the synchrotron experiment, however, showed an obvious break at pressure exceeding 4 GPa due to the loss of hydrostaticity. NiO in a nonhydrostatic condition behaves with less compressibility than the hydrostatic results with a nominal K _o of 238 ± 10 GPa. The lower compressibility of NiO in synchrotron runs is attributed to the uniaxial loading effect which was more easily detected by the EDXRD geometry. The discrepancy in the bulk modulus can be attributed to the contrast in the shear strength between the sample and pressure medium and the Poisson effect of the sample under uniaxial loading.     

High pressure X-ray diffraction and Raman spectroscopic studies of the phase change of D2O ice VII at approximately 11 GPa

High pressure experiments were performed on D₂O ice VII using a diamond anvil cell in a pressure range of 2.0–60 GPa at room temperature. In situ X-ray diffractometry revealed that the structure changed from cubic to a low symmetry phase at approximately 11 GPa, based on the observed splitting of the cubic structure's diffraction lines. Heating treatments were added for the samples to reduce the effect of non-hydrostatic stress. After heating, splitting diffraction lines became sharp and the splitting was clearly retained. Although symmetry and structure of the transformed phase have not been determined, change in volumes vs. pressure was calculated, assuming that the low-symmetry phase had a tetragonal structure. The bulk modulus calculated for the low-symmetry phase was slightly larger than that for the cubic structure. In Raman spectroscopy, the squared vibrational frequencies of ν₁ (A_1g), as a function of pressure, showed a clear change in the slope at 11–13 GPa. The full width at half maxima of the O-D modes decreased with increasing pressure, reaching a minimum at approximately 11 GPa, and increased again above 11 GPa. These results evidently support the existence of phase change at approximately 11 GPa for D₂O ice VII.     

High-pressure study of NaAlH4 by Raman spectroscopy up to 17 GPa

A high-pressure Raman study was carried out on NaAlH₄ up to 17 GPa using the diamond anvil cell method. In the pressure region 2–5 GPa, several of the original modes split. Although this might be a sign of some structural change, the spectral changes do not allow us to claim the existence of a clear phase transition in this pressure range. The spectra revert to their ambient pressure forms on decreasing pressure below<3.0–1.4 GPa. A phase transition to β-NaAlH₄ was found at 14–16 GPa. This phase transition is also reversible with an unusually strong hysteresis: the β-NaAlH₄ can be followed upon decompression down to 3.9 GPa. Analysis of Raman data shows that this phase transition is compatible with a theoretical prediction of a strong volume collapse.     

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.     

Distortion of spores of moss Venturiella under ultra high pressure

In our previous studies on the tolerance of living organisms such as planktons and spores of mosses to the high hydrostatic pressure of 7.5 GPa, we showed that all the samples could be borne at this high pressure. These studies have been extended to the extreme high pressure of 20 GPa by using a Kawai-type octahedral anvil press. It was found that the average diameter of the spores of Venturiella exposed to 20 GPa for 30 min was 25.5 μm, which is 16.5% smaller (40.0% smaller in volume) than that of the control group which was not exposed to high pressure. The inner organisms showed a further extent of plastic deformation. As a result, a gap appeared between the outer cover and the cytoplasm. A relationship has been obtained between the survival ratio and plastic deformation of spores of moss Venturiella caused by the application of ultra high pressure.     

Powder neutron diffraction of wüstite (Fe0.93O) to 12 GPa using large moissanite anvils

High-pressure powder neutron diffraction of wüstite-Fe_0.93O has been achieved to 12 GPa using a large gem-moissanite (SiC) anvil cell. The moissanite anvils are weakly absorbing and provide greater neutron fluxes to the sample than is possible with tungsten carbide anvils. There is minimal diffraction overlap from the single-crystal moissanite anvils compared to tungsten carbide or synthetic diamond anvils, providing cleaner background profiles. The required sample volume for high-pressure neutron diffraction is dramatically reduced to several cubic millimeters. High-quality powder diffraction patterns of wüstite were recorded at 90 min exposure times on the HIPPO diffractometer at LANSCE when the sample volume was in the range of ～10 mm³. This is about two orders of magnitude smaller than the necessary sample volume (～1.0 cm³) for the same kind of experiment with other high-pressure cells and nominal neutron fluxes.     

FEM study on a double-beveled anvil and its application to synthetic diamonds

A new double-beveled anvil for the synthesis of high-quality diamonds has been described, which is used in a China-type large-volume, cubic-anvil, high-pressure apparatus (LV-CHPA, SPD-6X2000). Our results indicate that the pressure generation of a double-beveled anvil is more efficient than that of a single-beveled anvil. To gain the same cell pressure (5.5 GPa), the oil pressure of LV-CHPA using double-beveled anvils decreased by about 10%, compared to using single-beveled anvils. Furthermore, a double-beveled anvil can pressurize a cubic cell of 36 mm³ up to about 6.0 GPa, and simultaneously can increase the temperature up to 1360°C for routine operation. This provides considerable advantages to the synthesis of high-quality diamonds under ultra-high-pressure conditions with the same hydraulic rams.     

Ruby under pressure

The ruby luminescence method is widely used for pressure measurement in the diamond anvil cell and other optically transparent pressure cells. With this application in mind, we briefly review the ground-state physical properties of corundum (α-Al₂O₃) with some emphasis on its behavior under high pressure, survey the effects of temperature and stress on the R-line luminescence of ruby (Cr-doped corundum), and address the recent efforts towards an improved calibration of the R-line shift under hydrostatic pressures beyond the 50 GPa mark.     

Phase transition of ZnS at high pressures and temperatures

The high-pressure behaviour of zinc sulphide, ZnS, has been investigated, using an in situ X-ray powder diffraction technique in a diamond anvil cell, at pressures and temperatures up to 35 GPa and 1000 K, respectively. The pressure-induced phase transition from a zincblende (B3) to a rocksalt (B1) structure was observed. This transition occurred at 13.4 GPa and at room temperature, and a negative dependence on temperature for this transition was confirmed. The transition boundary was determined to be P (GPa) = 14.4 ? 0.0033 × T (K).