Achievements in high‐pressure science at the high‐brilliance energy‐dispersive X‐ray absorption spectrometer of ESRF,ID24

Although the idea of an X‐ray absorption spectrometer in dispersive geometry was initially conceived for the study of transient phenomena, the instrument at the European Synchrotron Radiation facility has been increasingly exploited for studies at extreme conditions of pressure using diamond anvil cells. The main results of investigations at high pressure obtained at beamline ID24 are reviewed. These concern not only fundamental topics, such as the local and the electronic structure as well as the magnetic properties of matter, but also geological relevant questions such as the behaviour of Fe in the main components of the Earth's interior.     

Calibration of berlinite (AlPO4) as Raman spectroscopic pressure sensor for diamond‐anvil cell experiments at elevated temperatures

Changes in the band position of the 462 and the 1111 cm^–1 A₁ modes of berlinite (AlPO₄) with temperature and pressure were determined in situ to 500°C and to 10 GPa using Raman spectroscopy and diamond‐anvil cells. These bands shift in opposite directions with pressure and, likewise, with temperature. At a known temperature, the relative difference of both band positions (Δν)_P,T can therefore be used as a pressure gauge that does not require calibration of the spectrometer. At ambient pressure, the observed temperature dependence of this relative difference of the line positions is very close to linear and can be described by (Δν)_{T, 0.1 MPa} (cm^–1) = 0.0181 T – 0.46 where 23 ≤ T (°C) ≤ 500. Along the 23°C isotherm to 10 GPa, pressure and relative wavenumber difference (Δν)_{P, 23°C} are related by the equation P (GPa) = 0.00083 [(Δν)_{P, 23°C}]² – 0.062 (Δν)_{P, 23°C}. Both equations can be combined to determine pressures at higher temperatures under the assumption that the change in (Δν)_P,T with pressure is insensitive to temperature. Copyright © 2011 John Wiley & Sons, Ltd.     

Exploring the possible interlinked structures in single‐wall carbon nanotubes under pressure by Raman spectroscopy

High‐pressure Raman measurements on single‐wall carbon nanotubes (SWNTs) have been carried out in a diamond anvil cell by using two wavelength lasers: 830 and 514.5 nm. Irrespective of using a pressure transmitting medium (PTM) or not, we found that nanotubes undergo similar transformations under pressure. The pressure‐induced changes in Raman signals at around 2 and 5 GPa are attributed to the nanotube cross‐section transitions from circle to ellipse and then to a flattened shape, respectively. Especially with pressure increasing up to 15–17 GPa, we observed that the third transition takes place in both the Raman wavenumber and the linewidth of G‐band. We propose explanations that the interlinked configuration with sp³ bonds forms in the bundles of SWNTs under pressure, which was the cause for the occurrence of those Raman anomalies, similar to the structural‐phase transition of graphite above 14 GPa. Our TEM observations and Raman measurements on the decompressed samples support this transition picture. Copyright © 2012 John Wiley & Sons, Ltd.     

Raman G‐mode of single‐wall carbon nanotube bundles under pressure

Raman studies of nanotubes under pressure have been a lively area of research. However, the results are not always as expected and at times have not been adequately explained. One example of the diversity of the results is the higher energy Raman mode (the graphitic mode, GM) shift to higher wavenumber under pressure. Here we report a new high‐pressure Raman study showing that the effects of the variation in the tube diameters and the pressure transmitting medium are both crucial for understanding the outcomes of such high‐pressure experiments. Copyright © 2011 John Wiley & Sons, Ltd.     

Raman study of datolite CaBSiO4(OH) at simultaneously high pressure and high temperature

Using an in situ method of Raman spectroscopy and resistance‐heated diamond anvil cell, the system datolite CaBSiO₄(OH) – water has been investigated at simultaneously high pressure and temperature (up to Р ~5 GPa and Т ~250 °С). Two polymorphic transitions have been observed: (1) pressure‐induced phase transition or the feature in pressure dependence of Raman band wavenumbers at P = 2 GPа and constant T = 22 °С and (2) heating‐induced phase transition at T ~90 °С and P ~5 GPа. The number of Raman bands is retained at the first transition but changed at the second transition. The first transition is mainly distinguished by the changes in the slopes of pressure dependence of Raman peaks at 2 GPa. The second transition is characterized by several strong changes: the wavenumber jumps of major bands, the merging of strong doublets at 378 and 391 cm⁻¹ (values for ambient conditions), the splitting of the intermediate‐intensity band at 292 cm⁻¹, and the transformation of some low‐wavenumber bands at 160–190 cm⁻¹. No spectral and visual signs of overhydration and amorphization have been observed. No noticeable dissolution of datolite in the water medium occurred at 5 GPa and 250 °С after 3 h, which corresponds to typical conditions of the ‘cold’ zones of slab subduction. Copyright © 2014 John Wiley & Sons, Ltd.     

Substitution and proton doping effect on SrZrO3 behaviour: high‐pressure Raman study

The high‐pressure Raman studies of pure, Yb‐modified, protonated and non‐protonated SrZrO₃ dense ceramics were performed between 0.1 and 40 GPa using a diamond anvil cell. Lanthanide‐modified, protonated SrZrO₃ perovskites are potential materials for electrolytic membrane in fuel cells and electrolysers working at medium temperature. The comparison of the Raman spectra shows important differences in the pressure behaviour between the pure and Yb‐modified SrZrO₃ ceramics. SrZrO₃ exhibits a rigid structure without any structural modification, whereas for both SrZr_0.93 Yb_0.07 O_2.965 and SrZr_0.93 Yb_0.07 O_2.962 H_0.003 a sequence of structural modifications at 10, 20 and 35 GPa is revealed. The character of these structural modifications is very similar to that observed as a function of the temperature (orthorhombic Pnma 750 °C → pseudo‐tetragonal Imma 840 °C → tetragonal I4/mcm 1070 °C → cubic Pm3m), which suggests that they can be considered as the phase transitions. Despite the low level of proton content (0.3% mole/mole), significant difference between protonated and non‐protonated compounds is observed for the 700–750 cm⁻¹ doublet assigned to the Zr O octahedron stretching mode, perturbed by an oxygen atom vacancy and/or neighbouring Yb ion. The location of proton is discussed. Copyright © 2011 John Wiley & Sons, Ltd.     

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.     

Raman spectroscopy and magnetic properties of KMCr(CN)6 under pressure

We study the effect of pressure on Raman spectra as well on magnetic properties of molecule-based magnets KNiCr(CN)₆ and KMnCr(CN)₆. The effect of pressure on the ν[C≡N] vibration band which is located in the 2100–2200?cm^?1 spectral range is relatively weak. Hydrostatic pressure has small almost a negligible effect on the Curie temperature of ferromagnetic KNiCr(CN)₆ while leads to a pronounced reversible Curie temperature increase occurrence of new magnetic phase under pressure in the case of KMnCr(CN)₆. Applied pressure affects magnetization curves only marginally. All pressure-induced changes are reversible.     

High pressure Raman study on the local structure of 1-ethyl-3-methylimidazolium tetrafluoroborate

We have investigated the pressure-induced Raman spectral changes of 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF₄]). We found that [emim][BF₄] did not crystallize up to 1.2 GPa. The Raman CH stretching spectra arising from the CH₃ groups of the ethyl-chain and the CH₃ group adjacent to the imidazolium-ring in [emim]⁺ cation largely changed against pressure. Moreover, the Raman intensity of the CH₂ (N) bending band arising from the alkyl-chain drastically changes with increasing pressure, but that of the imidazolium-ring in-plane bending band arising from the imidazolium-ring is independent of pressure. Our results show that the environment around the alkyl-chain of [emim][BF₄] is largely perturbed rather than that around the imidazolium-ring upon compression.     

A high pressure Raman study of TeO2 to 30 GPa and pressure-induced phase changes

The effect of pressure on the Raman modes in TeO₂ (paratellurite) has been investigated to 30GPa, using the diamond cell and argon as pressure medium. The pressure dependence of the Raman modes indicates four pressure-induced phase transitions near 1 GPa, 4.5 GPa, 11 GPa and 22 GPa. Of these the first is the well studied second-order transition fromD ₄ ⁴ symmetry toD ₂ ⁴ symmetry, driven by a soft acoustic shear mode instability. The remarkable similarity in the Raman spectra of phases I to IV suggest that only subtle changes in the structure are involved in these phase transitions. The totally different Raman spectral features of phase V indicate major structural changes at the 22GPa transition. It is suggested that this high pressure-phase is similar to PbCl₂-type, from high pressure crystal chemical considerations. The need for a high pressure X-ray diffraction study on TeO₂ is emphasized, to unravel the structure of the various high pressure phases in the system.     

基于拉曼频移的白宝石压腔无压标系统高温高压实验标定

在高压实验科学中, 各类宝石压腔是最为常见的高压设备之一, 其样品腔中压力的精确标定是实验的关键. 目前, 人们主要通过加入红宝石等压标物质来进行定压, 但压标物质的加入会增加实验的装样难度, 改变样品腔中的物理化学环境, 甚至直接与实验样品发生反应, 从而对实验结果产生影响. 在0–6.3 GPa和300–573 K下, 利用共聚焦拉曼显微镜, 根据白宝石压砧砧面的ν₁₂ 拉曼频移与温度和压力的变化关系, 建立了一套适用于高温高压水热体系的无压标白宝石压腔系统. 实验结果表明: 白宝石砧面的ν₁₂ 峰随着压力的升高发生线性蓝移, 而随着温度升高则发生线性红移, 且温度和压力对拉曼频移的影响存在耦合效应. 利用本实验结果, 可在高温高压下根据白宝石砧面的拉曼频移计算出样品腔的压力P=(Δλ-0.01913×ΔT)/(1.9158-0.00105×ΔT), 在物理学、材料学和地球科学等领域具有重要应用.     

Momentum‐resolved resonant inelastic X‐ray scattering on a single crystal under high pressure

A single‐crystal momentum‐resolved resonant inelastic X‐ray scattering (RIXS) experiment under high pressure using an originally designed diamond anvil cell (DAC) is reported. The diamond‐in/diamond‐out geometry was adopted with both the incident and scattered beams passing through a 1 mm‐thick diamond. This enabled us to cover wide momentum space keeping the scattering angle condition near 90°. Elastic and inelastic scattering from the diamond was drastically reduced using a pinhole placed after the DAC. Measurement of the momentum‐resolved RIXS spectra of Sr_2.5Ca_11.5Cu₂₄O₄₁ at the Cu K‐edge was thus successful. Though the inelastic intensity becomes weaker by two orders than the ambient pressure, RIXS spectra both at the center and the edge of the Brillouin zone were obtained at 3 GPa and low‐energy electronic excitations of the cuprate were found to change with pressure.     

Structure,thermodynamic and transport properties of imidazolium-based bis(trifluoromethylsulfonyl)imide ionic liquids from molecular dynamics simulations

Molecular dynamics (MD) simulations have been performed in order to investigate the properties of [C _n mim⁺][Tf₂N^?] (n?=?4,?8,?12) ionic liquids (ILs) in a wide temperature range (298.15?498.15?K) and at atmospheric pressure (1 bar). A previously developed methodology for the calculation of the charge distribution that incorporates ab initio quantum mechanical calculations based on density functional theory (DFT) was used to calculate the partial charges for the classical molecular simulations. The wide range of time scales that characterize the segmental dynamics of these ILs, especially at low temperatures, required very long MD simulations, on the order of several tens of nanoseconds, to calculate the thermodynamic (density, thermal expansion, isothermal compressibility), structural (radial distribution functions between the centers of mass of ions and between individual sites, radial-angular distribution functions) and dynamic (relaxation times of the reorientation of the bonds and the torsion angles, self-diffusion coefficients, shear viscosity) properties. The influence of the temperature and the cation's alkyl chain length on the above-mentioned properties was thoroughly investigated. The calculated thermodynamic (primary and derivative) and structural properties are in good agreement with the experimental data, while the extremely sluggish dynamics of the ILs under study renders the calculation of their transport properties a very complicated and challenging task, especially at low temperatures.     

Preparation of a macrocrystalline pressure calibrant SrB4O7:Sm 2+ suitable for the HP-HT powder diffraction

A new simplified synthesis of monocrystalline chips of SrB₄O₇: Sm²⁺ pressure calibrant, well-suited for the diamond anvil cell (DAC) powder diffraction experiments, is proposed. It consists of ordinary solid-state synthesis of fine-grained SrB₄O₇: Sm²⁺ and subsequent annealing near melting temperature. The obtained material was characterized and tested in HP-HT DAC experiment.     

Solvation of AgTFSI in 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid investigated by vibrational spectroscopy and DFT calculations

In this paper we investigate the solvation of silver bis(trifluoromethylsulfonyl)imide salt (AgTFSI) in 1‐ethyl‐3‐methylimidazolium TFSI [EMI][TFSI] ionic liquid by combining Raman and infrared (IR) spectroscopies with density functional theory (DFT) calculations. The IR and Raman spectra were measured in the 200–4000 cm⁻¹ spectral region for AgTFSI/[EMI][TFSI] solutions with different concentrations ([AgTFSI] <0.2 mole fraction). The analysis of the spectra shows that the spectral features observed by dissolution of AgTFSI in [EMI][TFSI] solution originate from interactions between the Ag⁺ cation and the first neighboring TFSI anions to form relatively stable Ag complexes. The ‘gas phase’ interaction energy of a type [Ag(TFSI)₃]²⁻ complex was evaluated by DFT calculations and compared with other interionic interaction energy contributions. The predicted spectral signatures because of the [Ag(TFSI)₃]²⁻ complex were assessed in order to interpret the main IR and Raman spectral features observed. The formation of such complexes leads to the appearance of new interaction‐induced bands situated at 753 cm⁻¹ in Raman and at 1015 and 1371 cm⁻¹ in IR, respectively. These specific spectral signatures are associated with the ‘breathing’ mode and the S–N–S and S–O stretching modes of the TFSI anions engaged in the complex. Finally, all these findings are discussed in terms of interaction mechanisms enabling the electrodeposition characteristics of silver from AgTFSI/[EMI][TFSI] IL‐based electrolytic solutions. Copyright © 2015 John Wiley & Sons, Ltd.     

常温和100~800 MPa压力下石膏的Raman光谱研究

 利用金刚石压腔装置测量了高压下石膏中S—O键的4种振动模式和结晶水中羟基伸缩振动Raman位移，研究结果表明：在常温（25 ℃）和100~800 MPa压力范围内，石膏中S—O键的Raman谱峰的位移随压力的增加而向高波数方向移动，结晶水中羟基的两个伸缩谱峰随着压力的增加而向低波数方向移动，同时得到了各个谱峰与压力之间的关系式，其中结晶水中羟基的两个伸缩谱峰的dν/dp值有较大不同，是由于结晶水中含有两个强度不同的氢键所致。     

氨的半水合物的高压拉曼光谱研究

在室温条件下, 利用金刚石对顶砧超高压技术, 对氨的半水合物(2NH3·H2O) 进行了原位高压拉曼光谱研究, 采用红宝石荧光压标测压, 实验的最高压力为41.0 GPa。装入金刚石对顶砧样品腔的初始样品为液态的氨的半水合物, 当压力达到3.5 GPa时, 显微镜下观察到整个样品腔内均匀的出现块状晶体, 同时, 测量到的拉曼谱上出现许多新的拉曼峰。因此, 我们判断在此压力下液态的2NH3·H2O发生了液固相变。当压力增加到19.0 GPa左右时, 2NH3·H2O的拉曼频移随压力变化的曲线有拐点, 并且具有软化特性的N-H伸缩振动模式消失。我们分析这是因为在高压下, 通过O-H…N成键的II型氨分子发生了旋转, 所以2NH3·H2O在此压力下发生了一次固固相变。     

X‐ray magnetic spectroscopy at high pressure: performance of SPring‐8 BL39XU

An X‐ray magnetic circular dichroism experiment under multiple extreme conditions, 2 ≤T≤ 300 K, H≤ 10 T and P≤ 50 GPa, has been achieved at SPring‐8 BL39XU. A combination of the high‐brilliant X‐ray beam and a helicity‐controlled technique enabled the dichroic signal to be recorded with high accuracy. The performance is shown by the outcome of pressure‐induced ferromagnetism in Mn₃GaC and the pressure‐suppressed Co moment in ErCo₂. Two technical developments, a tiny diamond anvil cell inserted into a superconducting magnet and in situ pressure calibration using 90° Bragg diffraction from a NaCl marker, are also presented. X‐ray magnetic spectroscopy under multiple extreme conditions is now opening a new approach to materials science.     

Micro‐Raman and IR study of the compressive behaviour of poly(paraphenylene benzobisoxazole) (PBO) fibres in a diamond‐anvil cell

The micro/nano structural evolution of PBO (poly(paraphenylenebenzobisoxazole), commercial name Zylon) fibres has been studied by Raman and IR spectroscopy in a diamond‐anvil cell, up to ∼15 GPa. Different modes were considered in the 900–1700 cm⁻¹ (Raman) and 800–3300 cm⁻¹ (IR) spectral range. The material behaviour appears more similar to that of a densely packed inorganic structure than to the behaviour previously observed for polyamide fibres, and is related to the compact arrangement of the rigid heterocyclic rings. Wavenumber shift starts with increase in pressure and a transition between the two regimes was revealed at ∼2–2.5 GPa, and it was assigned to the loss of order between neighbouring PBO chains. A good correlation is observed between the macroscopic mechanical properties and the nanomechanics at the chemical bond scale. Copyright © 2006 John Wiley & Sons, Ltd.