ODE: a new beam line for high-pressure XAS and XMCD studies at SOLEIL

X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) under pressure are probes of local order and microscopic magnetic properties. XMCD is a selective probe that has access to a large variety of elements. The dispersive extended X-ray absorption fine structure (EXAFS) station at SOLEIL (ODE beam line) provides the possibility to perform numerous pressure XAS and XMCD experiments with an excellent statistic. The main advantages of dispersive XAFS are the focusing optics, the short acquisition time (few μs) and great stability during the measurements due to the absence of any mechanical movement. These advantages allow the study of small samples, 70 μm at SOLEIL, which is mandatory in the case of high-pressure studies. We present the new ODE beam line at SOLEIL and its first high-pressure XMCD results.     

钍基碳化物ThC的高压结构稳定性研究

钍基碳化物ThC是重要的核材料,基于第一性原理计算,我们研究了ThC的结构稳定性及相变.声子色散曲线表明基态结构的晶格能够稳定到42 GPa附近,当压力继续升高时虚频的出现表明了动力学的不稳定.经比较基态Fm-3m及高压相Pnma结构的自由能,发现零温下,相变压力为22.4 GPa,符合声子色散曲线的结果,同时预测了两种结构的相变边界.     

极端条件下锆的动力学稳定性研究

过渡金属Zr具有优良的物理、化学及力学性能, 具有广泛的应用价值. 主要通过新近发展的自洽晶格动力学方法, 充分考虑声子间的相互作用, 成功获得了β-Zr的高温高压声子色散曲线, 预测了β-Zr在相图中能够稳定存在的区域, 进一步比较α-Zr, ω-Zr和β-Zr的自由能, 获得了α-β 及ω-β 相变的相边界, 构建了Zr的参考相图. 同时, 也获得了β-Zr的高温状态方程及热膨胀系数, 能够为构建Zr的全区物态方程提供有益的参考.     

New materials from high pressure experiments: Challenges and opportunities

Recent improvements in high pressure techniques have led to new scientific discoveries in fields ranging from Earth and Planetary Science, to fundamental physics and biology. Here we examine the possibilities for development of new technologically-important materials based on high pressure research.     

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.     

The structural and optical properties of ZnO bulk and nanocrystals under high pressure

The elastic properties of high-quality ZnO crystals and nanopowder of grain size of about 65 nm are studied for both wurtzite (low pressure) and rock-salt high pressure phases. The measured values of bulk moduli for wurtzite and rock-salt phases of bulk ZnO crystals are equal to 156±13 and 187±20 GPa, respectively, and considerably larger for ZnO nanocrystals. The phase transition begins at a pressure of about 9 GPa and it is completed at a pressure of about 13.8 GPa for bulk crystals, whereas the values of pressure at which the phase transition occurs are lower for nanocrystals. A carefull Rietveld analysis of the obtained data does not exhibit the presence of any intermediate phases between low pressure wurtzite and high pressure rock-salt phases of ZnO. The phase transition is accompanied by a strong decrease in the near-band-gap photoluminescence intensity. In addition, the pressure coefficient of the near-band-gap luminescence in ZnO nanocrystals exhibits strong deviation from the linearity observed in bulk crystals. An analysis of the results shows that defects present in the nanopowdered sample are responsible for the observed effects.     

Determination of the phase boundary of GaP using in situ high pressure and high-temperature X-ray diffraction

The high pressure behavior of gallium phosphide, GaP, has been examined using the synchrotron X-ray diffraction technique in a diamond anvil cell up to 27?GPa and 900?K. The transition from a semiconducting to a metallic phase was observed. This transition occurred at 22.2?GPa and room temperature, and a negative dependence of temperature of this transition was found. The transition boundary was determined to be P (GPa)?=?22.6???0.0014?×?T (K).     

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 .     

Effect of very high pressure on the magnetic state of transition metal compounds

By simultaneously combining the methods of X-ray diffraction for structural phase transitions and EOS measurements, ⁵⁷Fe Mössbauer spectroscopy as a site-sensitive probe, and resistivity measurements for studying insulating-metal transitions, we are able to study the effect of extreme pressures and at varying temperature on magnetic and electronic properties of transition metal compounds. Studies are carried out with specially tailored diamond anvils and diamond anvil cells, reaching pressures beyond 100?GPa. From our studies, we can investigate the most basic phenomenon of the quantum effect of magnetism in insulating antiferromagnets, the Mott insulators, such as high to low spin crossovers, quenching of the magnetic moments' orbital term, and the collapse of the Mott–Hubbard state. Examples of these phenomena will be given in cases of ferrous and ferric oxides, ferrous-halides and the rare-earth iron perovskites.     

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.     

Combined X-ray absorption and X-ray diffraction under high pressure

ABSTRACT

X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) are two complementary structural techniques. Their combination improves the understanding of the effect of pressure on materials as illustrated by examples taken from studies on different types of materials (semiconductors, molecular solid, ferroelectric perovskite and gas mixture). The introduction of nanopolycrystalline diamonds anvils has extended XAS to high-energy edges with the possibility to use energy-scanning XAS beamlines where XRD can be performed in addition to XAS experiments.     

Phase transition of samarium under high pressure

Abstract

The DAC X-ray power photograph method was employed for studing the phase transition of samarium up to 26.3 GPa. The experimental results show that the dhcp and fcc high pressure phase of Sm appeared at about 4.0 and 12.5 GPa and room temperature respectively. The dhcp phase was kept until 19.6 GPa. A model for Sm-type -? dhcp -? fcc phase transition is provided in this paper.     

Structural and magnetic properties of MoS2 monolayer zigzag nanoribbon doped by Ti,V, Cr,and Mn

In order to find new functions of monolayer MoS₂ in nanoelectronics or spin electronic devices, using spin-polarized density functional theory (DFT) calculations with on-site coulomb interaction (U), we investigated substitutional doping of Mo atoms of monolayer zigzag MoS₂ nanoribbon (ZZ-MoS₂ NR) by transition metals (TM) (where TM = Ti, V, Cr, Mn) at the Mo-edge, S-edge, and the middle of the NRs. The results of this study indicate the NR widened irrespective of the doped TM position and type, and the Mo-edge was found as the easiest substitutional position. For ZZ-MoS₂ NR doped by Mn, Cr or V atoms, the preferred magnetic coupling state is the edge atoms of S at the S-edge, exhibiting the same spin polarization with TM (named the FM1 state), attributing the NR with metallic magnetism. For Ti-doped monolayer ZZ-MoS₂ NR, in addition to the FM1 state, other preferred magnetic coupling state was observed in which the edge atoms of S at the S-edge exhibit the opposite spin polarization with that of Ti (named the FM2 state). Thus, the NR doped by Ti atom possesses metallic (FM1 state) or half-metallic (FM2 state) magnetism. The total magnetic moments of the ZZ-MoS₂ NR doped by TM follows a linear relationship as a function of the TM dopants (Mn, Cr, V, and Ti). Under $>4\text{\%}$ applied strain, the NR doped by Ti atom only presents the characteristics of half-metallic magnetism as the initial one in the FM2 state, and its total magnetic moment always remained 0 μB, i.e., it was not affected by the width of the NR. This study provides a rational route of tuning the magnetic properties of ZZ-MoS₂ NRs for their promising applications in nanoelectronics and spin electronic devices.     

高压下物质性质的研究

概述了高压（力）下物质性质研究的方法、历史和最新发展。     

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.     

Structural transition of FeSe under high pressure

The density functional calculations of the energy band structure and density of state for the tetragonal PbO-type phase α-FeSe and hexagonal NiAs-type phase β-FeSe are reported in this paper. The structural phase transition from tetragonal to hexagonal FeSe under high pressure is investigated, it is found that the calculated transition pressure for the α → β phase transformation is 8.5 GPa. Some fluctuations in the transition pressure maybe occurred by different external factors such as temperature and stress condition. There is about 17% volume collapse accompanying the α → β phase transformation.