High-pressure Diffraction Experiments Research Articles

Experimental and computational study of the core-level crossing transition in iridium at high pressure

A core-level crossing (CLC) resulting from extreme compression has been calculated to occur in Ir metal at 80 GPa, analogous to a transition previously reported in Os at 392 GPa. We present results from static high-pressure diffraction experiments and theoretical investigations on the compressive behavior of Ir up to 159 GPa, well above the calculated CLC transition pressure. Neither our experimental nor computational results find evidence for a CLC over this pressure range, and instead, our first-principles calculations suggest that the CLC occurs in Ir at the much higher pressure of 400 GPa. Furthermore, computational analysis of the CLC in Ir, combined with previous work on Os, indicates that CLCs at high pressure are not experimentally detectable. Published by the American Physical Society 2024

Increasing completeness in single-crystal high-pressure diffraction experiments by pre-orienting crystals

Increasing completeness in single-crystal high-pressure diffraction experiments by pre-orienting crystals

Estimating completeness in single-crystal high-pressure diffraction experiments

Estimating completeness in single-crystal high-pressure diffraction experiments

Mapping completeness.

Tchoń & Makal [IUCrJ (2021), 8, 1006-1017] use numerical simulations to explore the dependence of data completeness on crystal orientation, X-ray energy and diamond anvil cell geometry for high-pressure diffraction experiments. Their completeness heat maps for different Laue classes can be used to guide optimization of high-pressure single-crystal diffraction experiments.

Maximizing completeness in single-crystal high-pressure diffraction experiments: phase transitions in 2°AP.

Sufficiently high completeness of diffraction data is necessary to correctly determine the space group, observe solid-state structural transformations or investigate charge density distribution under pressure. Regrettably, experiments performed at high pressure in a diamond anvil cell (DAC) yield inherently incomplete datasets. The present work systematizes the combined influence of radiation wavelength, DAC opening angle and sample orientation in a DAC on the completeness of diffraction data collected in a single-crystal high-pressure (HP) experiment with the help of dedicated software. In particular, the impact of the sample orientation on the achievable data completeness is quantified and proved to be substantial. Graphical guides for estimating the most beneficial sample orientation depending on the sample Laue class and assuming a few commonly used experimental setups are proposed. The usefulness of these guides has been tested in the case of luminescent 1,3-diacetylpyrene, suspected to undergo transitions from the α phase (Pnma) to the γ phase (Pn21 a) and δ phase (P1121/a) under pressure. Effective sample orientation has ensured over 90% coverage even for the monoclinic system and enabled unrestrained structure refinements and access to complete systematic extinction patterns.

Extending the single-crystal quartz pressure gauge up to hydrostatic pressure of 19 GPa

In situ high-pressure diffraction experiments on single-crystal α-quartz under quasi-hydrostatic conditions up to 19 GPa were performed with diamond-anvil cells. Isotropic pressures were calibrated through the ruby-luminescence technique. A 4:1 methanol–ethanol mixture and the densified noble gases helium and neon were used as pressure media. The compression data revealed no significant influence of the pressure medium at room temperature on the high-pressure behavior of α-quartz. In order to describe its compressibility for use as a pressure standard, a fourth-order Birch–Murnaghan equation of state (EoS) with parameters K T0 = 37.0 (3) GPa, K T0′ = 6.7 (2) and K T0′′ = −0.73 (8) GPa−1 was applied to fit the data set of 99 individual data points. The fit of the axial compressibilities yields M T0 = 104.5 (8) GPa, M T0′ = 13.7 (4), M T0′′ = −1.04 (11) GPa−1 (a axis) and M T0 = 141 (3) GPa, M T0′ = 21 (2), M T0′′ = 8.4 (6) GPa−1 (c axis), confirming the previously reported anisotropy. Assuming an estimated standard deviation of 0.0001% in the quartz volume, an uncertainty of 0.013 GPa can be expected using the new set of EoS parameters to determine the pressure.

Gallium Arsenate Dihydrate under Pressure: Elastic Properties, Compression Mechanism, and Hydrogen Bonding.

Gallium arsenate dihydrate is a member of a class of isostructural compounds, with the general formula M(3+)AsO4·2H2O (M(3+) = Fe, Al, In, or Ga), which are being considered as potential solid-state storage media for the sequestration of toxic arsenic cations. We report the first high-pressure structural analysis of a metal arsenate dihydrate, namely, GaAsO4·2H2O. This compound crystallizes in the orthorhombic space group Pbca with Z = 8. Accurate unit cell parameters as a function of pressure were obtained by high-pressure single-crystal X-ray diffraction, and a bulk modulus of 51.1(3) GPa for GaAsO4·2H2O was determined from a third-order Birch-Murnaghan equation of state fit to the P-V data. Assessment of the pressure dependencies of the unit cell lengths showed that the compressibility of the structure along the axial directions increases in the order of [010] < [100] < [001]. This order was found to correlate well with the proposed compression mechanism for GaAsO4·2H2O, which involves deformation of the internal channel void spaces of the polyhedral helices that lie parallel to the [010] direction, and increased distortion of the GaO6 octahedra. The findings of the high-pressure diffraction experiment were further supported by the results from variable-pressure Raman analysis of GaAsO4·2H2O. Moreover, we propose a revised and more complex model for the hydrogen-bonding scheme in GaAsO4·2H2O, and on the basis of this revision, we reassigned the peaks in the OH stretching regions of previously published Raman spectra of this compound.

Single-crystal X-ray diffraction at extreme conditions: a review

The latest developments in single-crystal X-ray diffraction at high pressure and high temperature are described. Advances in diamond anvil cell designs and X-ray sources allow collecting single-crystal diffraction data at pressures up and above 100 GPa and at temperatures above 1000°C. The technical details of single-crystal X-ray diffraction at high pressure such as the choice of pressure-transmitting media or the different methods for measuring pressures and temperatures have been reviewed. Examples of structural solution of complex structures and new materials, structural refinements of high pressure polymorphs as well as accurate compressibility data are described in order to outline the several advantages of using single crystals instead of powdered samples in high pressure diffraction experiments.

A novel facility using a Laue focusing monochromator for high-pressure diffraction at the SRS, Daresbury, UK

A novel Laue focusing monochromator has been developed to provide intense X-radiation for high-pressure diffraction experiments. A beamline using this monochromator has been successfully developed on station 9.5 at the SRS, Daresbury Laboratory. Contributions to resolution from monochromator bandpass and divergence due to focusing have been quantified and are used to assess experimental diffraction data from diamond-anvil cells recorded using image plates with X-rays at approximately 30 keV. This optical and beamline design could be readily adapted to use X-rays from a bending magnet on a third-generation synchrotron source.

High‐Pressure Investigation of Sr3PbNiO6.

AbstractFor Abstract see ChemInform Abstract in Full Text.

High-pressure investigation of Sr 3PbNiO 6

High-pressure diffraction experiments on Sr 3PbNiO 6, a 2H-perovskite related oxide, were performed using a diamond anvil cell (DAC) and synchrotron radiation to investigate the structural chemistry and to determine the bulk modulus. The pressure dependence of unit cell parameters was determined for pressures up to 6.5(1) GPa, which revealed a uniform decrease in the lattice parameters and in the unit cell volume. Sr 3PbNiO 6 does not exhibit any phase transition in the pressure range investigated. A fit of the volume–pressure data using the Murnaghan equation of state yielded a bulk modulus of 95(2) GPa.

High-pressure structural and optical properties of wurtzite-type Zn1−xMgxSe

High-pressure diffraction experiments for wurtzite-type zinc magnesium selenide were performed using a large-anvil X-ray diffraction press, MAX80, and synchrotron radiation. The pressure dependence of unit-cell parameters was determined for Zn0.53Mg0.47Se for pressures ranging up to 5.17GPa. The value of bulk modulus and its pressure derivative were calculated from the pressure–volume dependence by fitting the Birch–Murnaghan equation of state (EOS). They are compared with reported data for ZnSe, MgSe and some related solid solutions. Photoluminescence (PL) data for Zn0.38Mg0.62Se were collected using a diamond-anvil cell at a lower pressure. These data show an evolution of the main deep-levels emission band: a narrowing of the spectrum, an increase of luminescence intensity and a blue shift.

Structural Refinements on Restricted Intensity Data Collected in High-Pressure Diffraction Experiments

Structural Refinements on Restricted Intensity Data Collected in High-Pressure Diffraction Experiments

High-energy X-ray diffraction beamline: BL04B2 at SPring-8

High-energy X-ray diffraction beamline, one of the bending-magnet beamline at SPring-8, was constructed, for the diffraction and scattering experiments at high energy ( E>37.8 keV). A single-bounce, bent-crystal monochromator that deflects the beam horizontally is adopted for the use of high-energy, modest-resolution, and focused X-rays. Four kinds of experimental device were equipped in tandem in the experimental hutch. This beamline has the advantage for structural studies in amorphous and liquid, and high-pressure diffraction experiments which need high penetration ability.

Equations of State

Diffraction experiments at high pressures provide measurement of the variation of the unit-cell parameters of the sample with pressure and thereby the variation of its volume (or equivalently its density) with pressure, and sometimes temperature. This last is known as the ‘Equation of State’ (EoS) of the material. It is the aim of this chapter to present a detailed guide to the methods by which the parameters of EoS can be obtained from experimental compression data, and the diagnostic tools by which the quality of the results can be assessed. The chapter concludes with a presentation of a method by which the uncertainties in EoS parameters can be predicted from the uncertainties in the measurements of pressure and temperature, thus allowing high-pressure diffraction experiments to be designed in advance to yield the required precision in results. The variation of the volume of a solid with pressure is characterised by the bulk modulus, defined as K = − V ∂ P /∂ V . Measured equations of state are usually parameterized in terms of the values of the bulk modulus and its pressure derivatives, K′ = −∂ K /∂ P and K″ = −∂2 K /∂ P 2, evaluated at zero pressure. These zero-pressure (or, almost equivalent, the room-pressure values) are normally denoted by a subscript “0,” thus: K = − V (∂ P /∂ V ) P =0, K ′ = −(∂ K /∂ P ) P =0, and K ″ = −(∂2 K /∂ P 2) P =0. However, throughout this chapter a number of notational conventions are followed for ease of presentation. Unless specifically stated, the symbols K′ and K ″ (without subscript) refer to the zero-pressure values at ambient temperature, all references to bulk modulus, K …

Microfocusing of Hard X-rays with Cylindrically Bent Crystal Monochromators

High-energy X-ray focusing with bent-crystal monochromators is known to be hampered by so-called depth or crystal-thickness aberrations. A theoretical model of focus broadening based on the geometrical theory of X-ray diffraction in slightly deformed crystals is presented and compared with experimental data. First, it is shown that depth broadening can be avoided in the Laue geometry by an appropriate choice of asymmetry angle. Based on this finding, a monochromator for high-pressure diffraction experiments has been designed and a source-size-limited focal spot below 10 microns is observed. As a consequence of the box-shaped rocking curve of bent Laue crystals, the focus is free of long-ranging tails. Diffraction patterns of standard powder samples were recorded on imaging plates and a theoretical description of the energy-dispersion-related peak broadening is given. Finally, diffraction patterns of N2 at 180 kbar demonstrate the excellent data quality achievable with this monochromator.

Modeling of strain distribution in non-hydrostatically pressed nanocrystalline sic; in-situ x-ray diffraction study

ABSTRACTGrain size and strain distribution functions of polycrystals of SiC with nanosize grains were examined based on X-ray diffraction data and ab initio calculations of scattered intensity from Debye functions. A tentative model of distribution of strain induced under high isostatic pressure in nanoparticles with different grain size is presented. Nanocrystalline SiC powders with grains down to 80Å in diameter were examined. In situ high pressure diffraction experiments were performed in cubic anvil cell MAX80 (up to 6 GPa) and in Diamond Anvil Cell (DAC) (up to 45 GPa) at HASYLAB, Hamburg, Germany. Shape of the Bragg lines was analysed with the use of two methods: (i) calculation of theoretical diffraction patterns based on modeling of one-dimensional disordering and ab initio calculation of scattered intensity starting from Debye functions and, (ii) approximation of the experimental shape of Bragg reflections by a combination of two functions: Gaussian (G) and Lorentzian (L).

Neutron scattering and μSR studies of fullerenes and their derivatives

The results of recent neutron scattering and μSR studies on C60 and C70 fullerenes and their derivatives in the solid state are briefly reviewed. Particular attention is paid to the temperature evolution of the rotational dynamics and the phase transitions accompanying orientational ordering. The potential of muons as spin labels both inside and outside the fullerene cage is also explored. Solid C60 shows a first-order phase transition at 260 K from a face-centred to a simple cubic structure. The isotropic molecular reorientations change abruptly to quasi-random jump motion between nearly-degenerate orientations differing in energy by 11.4(3) meV. A transition to an orientational glass state occurs at 85 K. Static disorder dominates the crystal chemistry of C70. The orientational ordering transitions from the high temperature face-centred cubic structure to the low temperature rhombohedral and monoclinic structures are accompanied by severe hysteresis effects. The rotational dynamic behaviour changes progressively on cooling from isotropic to anisotropic to uniaxial reorientations about the unique molecular axis. High pressure diffraction experiments reveal that C70 has a smaller compressibility than C60. Disorder effects are also present well in the superconducting state for the potassium fulleride K3C60. Small-amplitude librational motion of the C603− units is evident up to 650 K.

High-pressure facilities at the ESRF

Abstract Several beamlines at the European Synchrotron Radiation Facility in Grenoble are being designed with high-pressure experiments in mind. Among the first seven beamlines the Microfocus Beamline, the Materials Science Beamline, the Laue White Beamline and the High Energy Beamline are of particular interest for high-pressure diffraction experiments. These experimental stations are outlined and their characteristics are compared. Presented at the IUCr Workshop on ‘Synchrotron Radiation Instrumentation for High Pressure Crystallography’, Daresbury Laboratory 20-21 July 1991

Application of an imaging plate to high-pressure x-ray study with a diamond anvil cell (invited)

In order to obtain reliable data on d values and integrated intensities, an imaging plate (IP) has been applied to high-pressure diffraction experiments with a diamond anvil cell using synchrotron radiation. The IP was found to be more effective than a conventional x-ray film by a factor of 30, and more effective than an energy dispersive method by several times. In order to integrate the intensity data on the IP, a histogram method was successfully developed. This combination proved to give a lattice constant with relative accuracy of 2×10−4, and observed integrated intensities which excellently agree with calculated ones.