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.     

Measurement of diffusion process of iron atoms under high pressure of hydrogen by time-domain analysis of nuclear resonant scattering of X-rays

We applied the time-domain analysis of nuclear resonant scattering (NRS) of X-rays for the study of the hydrogen-induced enhancement of atomic diffusion. The time-domain analysis of NRS is a powerful technique for studying diffusion processes on an atomic scale. The NRS measurement combined with high-pressure technique enables the direct measurement of self-diffusion processes under high hydrogen pressures. In this preliminary experiment, self-diffusion in 4 μm thick ⁵⁷Fe foils at 0.8 GPa was investigated. The samples of the ⁵⁷Fe were encapsulated with MgO or NaCl. Faster decays caused by diffusion of Fe atoms were observed in the time spectra of NRS at high temperatures. This enhancement of diffusion is believed to be the hydrogen-induced effect. In the present experiment, hydrogen should have been supplied to the samples by reaction with water originally adsorbed on NaCl/MgO powder particles. It was concluded that the diffusion of ⁵⁷Fe atoms under high pressure can be studied by nuclear resonant scattering of X-rays using a compact cubic-anvil press. The NRS method can also be extended to the study of atomic diffusion in the subsurface region by doping ⁵⁷Fe layer(s) at known depths.     

RixsToolBox: software for the analysis of soft X‐ray RIXS data acquired with 2D detectors

A software with a graphical user interface has been developed with the aim of facilitating the data analysis for users of a new resonant inelastic X‐ray scattering (RIXS) spectrometer installed at the ESRF beamline ID32. The software is organized in modules covering all relevant steps in the data reduction from a stack of several hundred two‐dimensional CCD images to a single RIXS spectrum. It utilizes both full charge integration and single‐photon centroiding to cope with high‐flux and high‐resolution requirements. Additional modules for further data analysis and the extraction of instrumental parameters are available. The software has been in routine use for about a year now and in that time many additional features have been incorporated. It now meets the users' need for an easy‐to‐use data analysis tool that allows looking at and understanding data as it is acquired and thus steering users' experiments more efficiently.     

Charge density study under high pressure

The experimental and analytical method of the high-pressure powder experiment at BL10XU, SPring-8, is described. There is no doubt that BL10XU must be one of the most appropriate beam lines for high pressure X-ray diffraction experiment taking advantage of third generation synchrotron source. As an example of the advanced charge density study under high pressure, the structural change of Cs₂Au₂Br₆ by applying pressure is studied by Rietveld/MEM analysis. It reveals that the structural change of Cs₂Au₂Br₆ by applying pressure occurs basically at electron level, such as valence state change and chemical bonding, which may be called the electronic phase transition.     

Inorganic chemistry under high pressure

Abstract

In inorganic chemistry High Pressures can act as thermodynamic parameter and through the compression effect. Such effects can help the synthesis of new materials or induce specific properties. Such High Pressures studies are a great help for a better understanding of the chemical bonding and in field of resarches aimed at applications.     

An extraction algorithm for core‐level excitations in non‐resonant inelastic X‐ray scattering spectra

Non‐resonant inelastic X‐ray scattering of core electrons is a prominent tool for studying site‐selective, i.e. momentum‐transfer‐dependent, shallow absorption edges of liquids and samples under extreme conditions. A bottleneck of the analysis of such spectra is the appropriate subtraction of the underlying background owing to valence and core electron excitations. This background exhibits a strong momentum‐transfer dependence ranging from plasmon and particle–hole pair excitations to Compton scattering of core and valence electrons. In this work an algorithm to extract the absorption edges of interest from the superimposed background for a wide range of momentum transfers is presented and discussed for two examples, silicon and the compound silicondioxide.     

Compressibility of Fe1.087Te: a high pressure X-ray diffraction study

Fe_1.087Te exhibits three phases in the pressure range from ambient to 16.6?GPa and becomes amorphous at higher pressures. All three phases have tetragonal symmetry. The low pressure T-phase is stable in the pressure range 0≤P<4.1?GPa and is found to be relatively soft having zero pressure bulk modulus B ₀=36(1)?GPa. The intermediate cT-phase is less compressible with B ₀=88(5)?GPa and stable in the pressure range 4.1≤P<10?GPa while a more compressible phase was observed between 10 and 16.6?GPa.     

同步辐射X射线光源在高压科学研究中的应用

同步辐射X射线光源已经成功地应用到高压科学研究的诸多领域.文章简要回顾了同步辐射高压技术的发展历史,简要介绍了同步辐射X射线衍射技术在高压状态方程、强关联体系、地球内部物质以及早期生命起源等研究中的应用.介绍了同步辐射X射线光谱技术(包括晶格振动声子谱的测量)在高压研究中的应用,此外,还介绍了时间分辨的同步辐射技术在冲击压缩研究中的应用,最后展望了未来先进光源应用于高压科学研究的前景.     

原位高压测试技术在高压结构及性质研究中的应用

高压科学是研究不同压力条件下物质的结构、状态、理化性质及变化规律的学科。在高压科学研究中,多以凝聚态物质为研究对象,涉及的领域也非常广泛,包括物理学、化学、材料学、地质学、生物学、航天学等等,是一门以实验为基础的学科。高压科学之所以能成为一门独立的学科,还因为高压研究需要使用特殊且精巧的技术和方法来实现,是以技术创新为牵引的科学研究领域。而今,各种实验测试手段已经可以成熟地运用在该学科中,比较常见的有：高压拉曼散射、高压红外光谱、高压布里渊散射、高压同步辐射XRD、高压电学测量以及高压磁学测量等诸多技术。文章系统介绍了以上高压原位实验测试方法的原理、发展、作用及应用,有助于读者对原位高压测试技术有更深刻的认识和理解,为更高压力下的原位高压探测技术的发展提供重要的基础和借鉴。     

Phase transformations in amorphous fullerite C60 under high pressure and high temperature

First phase transformations of amorphous fullerite C₆₀ at high temperatures (up to 1800 K) and high pressures (up to 8 GPa) have been investigated and compared with the previous studies on the crystalline fullerite. The study was conducted using neutron diffraction and Raman spectroscopy. The amorphous fullerite was obtained by ball-milling. We have shown that under thermobaric treatment no crystallization of amorphous fullerite into С₆₀ molecular modification is observed, and it transforms into amorphous-like or crystalline graphite. A kinetic diagram of phase transformation of amorphous fullerite in temperature–pressure coordinates was constructed for the first time. Unlike in crystalline fullerite, no crystalline polymerized phases were formed under thermobaric treatment on amorphous fullerite. We found that amorphous fullerite turned out to be less resistant to thermobaric treatment, and amorphous-like or crystalline graphite were formed at lower temperatures than in crystalline fullerite.     

高温高压下草酸脱羧反应中的拉曼光谱研究

应用水热金刚石压腔结合拉曼光谱技术研究了高温高压下草酸溶液的热稳定,使用拉曼光谱对其脱羧反应及产物进行监测。结果表明低温升温过程中,草酸的拉曼谱图中各个特征振动峰没有发生变化,随着温度的继续升高,其特征振动峰逐渐变弱。达到一定温度后,羧基的拉曼特征峰消失,草酸发生脱羧反应:C2H2O4—2CO2+H2生成CO2和H2。高温高压下草酸发生热分解的温度压力之间呈线性关系,其线性回归方程为P(MPa)=12.839 T(K)-5 953.7,R2=0.99。草酸脱羧反应的摩尔体积变化与温度压力的关系为ΔV(cm-3.mol-1)=16.69-0.002P(MPa)+0.005 2T(K),R2=0.99。     

Structural, electronic, and magnetic properties of CrN under high pressure

The structural,electronic and magnetic properties of CrN under high pressure are investigated by first-principles calculations.The antiferromagnetic orthorhombic structure is identified to be the preferred ground state structure.It possesses a bulk modulus of 252.8 GPa and the nonzero magnetic moment of 2.33 μ B per Cr ion,which agree well with the experimental results.CrN undergoes structural and magnetic transitions from an antiferromagnetic rocksalt structure to a non-magnetic Pnma phase at 132 GPa.Under compression,the magnetic moment of the Cr ion reduces rapidly near the equilibrium and phase transition point,and the distribution of the density of states is broadened,but the form of overlap between the orbitals of Cr d and N p remains unchanged.The broadening of the band induces spin flipping,which consequently results in the smaller magnetic moment of the Cr ion.     

Modified Bridgman anvils for high pressure synthesis and neutron scattering

ABSTRACT

A simple modified Bridgman design for large volume pressure anvils usable in the Paris-Edinburgh (PE) press has been demonstrated at Oak Ridge National Laboratory Spallation Neutron Source. The design shows advantages over the toroidal anvils typically used in the PE press, mainly rapid compression/decompression rates, complete absence of blow-outs upon drastic phase transitions, simplified cooling, high reliability, and relative low loads (～40 tons) corresponding to relatively high pressures (～20?GPa). It also shows advantages over existing large-volume diamond cells as sample volumes of ～2–3?mm³ can be easily and rapidly synthesized. The anvils thus allow sample sizes sufficient for in situ neutron diffraction as well as rapid synthesis of adequate amounts of new materials for ex situ analysis via total neutron scattering and neutron spectroscopy.     

Co掺杂ZnO薄膜的局域结构和电荷转移特性研究

采用磁束缚电感耦合等离子体溅射沉积法在不同的氧气分压下制备了Zn_0.95Co_0.05O和Zn_0.94Co_0.05Al_0.01O薄膜.利用X射线吸收精细结构技术对薄膜O-K,Co-K和Co-L边进行了局域结构研究,结果表明：Co²⁺取代了四配位晶体场中的Zn²⁺而未改变ZnO的六方纤锌矿结构,高真空条件下制备的薄膜 关键词： Co掺杂ZnO 稀磁半导体 X射线吸收精细结构 共振非弹性X射线散射     

Probing the local,electronic and magnetic structure of matter under extreme conditions of temperature and pressure

ABSTRACT

In this paper we present recent achievements in the field of investigation of the local, electronic and magnetic structure of the matter under extreme conditions of pressure and temperature. These results were obtained thanks to the coupling of a compact laser heating system to the energy-dispersive XAS technique available on the ID24 beamline at the ESRF synchrotron. The examples chosen concern the melting and the liquid structure of 3d metals and alloys under high pressures (HPs) and the observation of temperature-induced spin crossover in FeCO₃ at HP.     

Raman spectra for hydrogen hydrate under high pressure: Intermolecular interactions in filled ice Ic structure

Raman studies of a high-pressure structure of hydrogen hydrate, a filled ice Ic structure, were performed using a diamond anvil cell in the pressure range 3.2-44.1 GPa. The Raman spectra of a vibron revealed that extraction of hydrogen molecules from the filled ice Ic structure occurred above 20 GPa. In addition, the Raman spectra of a roton revealed that a rotation of hydrogen molecules in the filled ice Ic structure was suppressed at around 20 GPa and then the rotation recovered, and the rotation of hydrogen molecules was suppressed again above 35.5 GPa. These results indicate that intermolecular interactions increased between guest hydrogen molecules and host water molecules at around 20 and 35.5 GPa. These intermolecular interactions were considered to be induced to stabilize the filled ice Ic structure. Above 40 GPa, symmetrization of hydrogen bond was considered to contribute to the stability of hydrogen hydrate.     

Electronic and magnetic studies of materials to megabar pressures

Numerous recent developments in diamond-cell techniques are making possible a growing range of studies of the electronic and magnetic properties of materials to megabar pressures. We review recent advances in this area, including magnetic susceptibility, electrical conductivity, and synchrotron-based spectroscopic techniques. Highly sensitive magnetic susceptibility techniques have allowed the first observations of superconductivity at megabar pressures, including the observation of a T_c of 17 K in sulfur at 160 GPa, and a nearly pressure-independent T_c to above 230 GPa. The technique has recently been extended to allow measurements of the magnetic properties of ferromagnetic substances. Advances in the direct measurement of electrical conductivity using miniaturized leads have permitted measurements on H₂O and Xe to above 100 GPa. Pressure-induced high-spin to low-spin transitions have been examined in FeS and FeO using new high-resolution X-ray emission techniques. New high-pressure inelastic scattering methods, including nuclear inelastic scattering techniques, have been used to determine the phonon density of states of Fe to above 150 GPa. This revised version was published online in July 2006 with corrections to the Cover Date.     

Shear induced phase transition in PbO under high pressure

We have studied the structural behavior of lead monoxide (PbO) as a function of pressure via angular dispersive X-ray diffraction employing two different pressure transmitting media that were quasi-hydrostatic (N₂) and non-hydrostatic (MgO), respectively. Besides litharge (-PbO) and massicot (β-PbO), which are both stable at ambient pressure, there is an orthorhombic γ-PbO phase which appears upon application of pressure to -PbO. We have found that the orthorhombic γ-PbO phase is favored by shear stress under non-hydrostatic conditions. -PbO shows strong anisotropy in compressibility. The a-axis is rather incompressible with a linear stiffness coefficient of K_a0=540(30) GPa whereas the c-axis stiffness is K_c0=25(1) GPa. The bulk modulus of -PbO is K₀=23.1(3) GPa and its derivative .     

Elemental sulfur under high hydrostatic pressure. An up-to-date Raman study

We report a high pressure Raman study of orthorhombic elemental sulfur from ambient pressure to ～ 25 GPa. Using a near infrared laser and low laser intensity on the scattering volume, we achieve off-resonant conditions up to larger pressures in comparison with previous studies. Raman spectra were recorded over the full spectral range including external (librational, translational) and internal (bond bending and bond stretching) modes. Drastic changes are observed as regards the peak frequencies, relative intensities and band splitting of degenerate modes. The main outcome of the present study is the observation of a “structural” transition at ～ 16 GPa manifested as slope changes of certain frequencies and sudden relative intensities changes. The present findings are discussed in the context of previous pressure Raman studies and comparison with existing X-ray diffraction as well as ab initio molecular dynamics results is attempted.