Center for Science at Extreme Conditions

Edinburgh, United Kingdom

Center for Science at Extreme Conditions

Edinburgh, United Kingdom

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Berg M.T.L.,University of Edinburgh | Bromiley G.D.,University of Edinburgh | Bromiley G.D.,Center for Science at Extreme Conditions | Butler I.B.,University of Edinburgh | And 11 more authors.
Physics of the Earth and Planetary Interiors | Year: 2017

The planets and larger rocky bodies of the inner solar system are differentiated, and consist of metallic, iron-rich cores surrounded by thick shells of silicate. Core formation in these bodies, i.e. the segregation of metal from silicate, was a key process in the early solar system, and one which left a lasting geochemical signature. It is commonly assumed that extensive silicate melting and formation of deep magma oceans was required to initiate core formation, due to the inability of iron-rich melts to segregate from a solid silicate matrix. Here we assess the role of deformation in aiding segregation of core-forming melts from solid silicate under conditions of planetary deep interiors. Low-strain rate, high-pressure/temperature deformation experiments and high-resolution 2-D and 3-D textural analysis demonstrate that deformation fundamentally alters iron-rich melt geometry, promoting wetting of silicate grain boundaries and formation of extensive micron to sub-micron width Fe-rich melt bands. Deformation-aided Fe-S melt networks noted here contrast those observed in higher finite strain experiments conducted at lower pressure, and may reveal either an alternative mechanism for melt segregation at higher pressures, or an early stage process of melt segregation. Results suggest, however, that core-mantle chemical equilibration cannot be assumed in models of planetary formation, and that instead, the chemistry of rocky planets may record a complex, multi-stage process of core formation. © 2017


Moretti Sala M.,European Synchrotron Radiation Facility | Schnells V.,University of Würzburg | Boseggia S.,University College London | Boseggia S.,Diamond Light Source | And 16 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2015

The magnetic excitation spectrum in the bilayer iridate Sr3Ir2O7 has been investigated using high-resolution resonant inelastic x-ray scattering (RIXS) performed at the iridium L3 edge and theoretical techniques. A study of the systematic dependence of the RIXS spectrum on the orientation of the wave-vector transfer Q, with respect to the iridium-oxide bilayer, has revealed that the magnon dispersion is comprised of two branches well separated in energy and gapped across the entire Brillouin zone. Our results contrast with those of an earlier study which reported the existence of a single dominant branch. While these earlier results were interpreted as two overlapping modes within a spin-wave model of weakly coupled iridium-oxide planes, our results are more reminiscent of those expected for a system of weakly coupled dimers. In this latter approach, the lower- and higher-energy modes find a natural explanation as those corresponding to transverse and longitudinal fluctuations, respectively. We have therefore developed a bond-operator theory which describes the magnetic dispersion in Sr3Ir2O7 in terms of quantum dimer excitations. In our model, dimerization is produced by the leading Heisenberg exchange Jc, which couples iridium ions in adjacent planes of the bilayer. The Hamiltonian also includes in-plane exchange J, as well as further neighbor couplings and relevant anisotropies. The bond-operator theory provides an excellent account of the dispersion of both modes, while the measured Q dependence of the RIXS intensities is in reasonable qualitative accord with the spin-spin correlation function calculated from the theory. We discuss our results in the context of the quantum criticality of bilayer dimer systems in the presence of anisotropic interactions derived from strong spin-orbit coupling. ©2015 American Physical Society.


Vale J.G.,University College London | Vale J.G.,Ecole Polytechnique Federale de Lausanne | Boseggia S.,University College London | Boseggia S.,Diamond Light Source | And 12 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2015

The magnetic critical scattering in Sr2IrO4 has been characterized using x-ray resonant magnetic scattering (XRMS) both below and above the three-dimensional antiferromagnetic ordering temperature TN. The order parameter critical exponent below TN is found to be β=0.195(4), in the range of the two-dimensional (2D) XYh4 universality class. Over an extended temperature range above TN, the amplitude and correlation length of the intrinsic critical fluctuations are well described by the 2D Heisenberg model with XY anisotropy. This contrasts with an earlier study of the critical scattering over a more limited range of temperature, which found agreement with the theory of the isotropic 2D Heisenberg quantum antiferromagnet, developed to describe the critical fluctuations of the conventional Mott insulator La2CuO4 and related systems. Our study therefore establishes the importance of XY anisotropy in the low-energy effective Hamiltonian of Sr2IrO4, the prototypical spin-orbit Mott insulator. © 2015 American Physical Society. ©2015 American Physical Society.


Gould J.A.,University of Liverpool | Rosseinsky M.J.,University of Liverpool | Warren J.E.,Daresbury Laboratory | Moggach S.A.,Center for Science at Extreme Conditions
Zeitschrift fur Kristallographie | Year: 2014

The hydrostatic compression of the chiral metal-organic framework [Ni(L-Asp)(H2O)2] · H2O (NiAsp-I) has been studied to 6.07 GPa by single crystal X-ray diffraction. Over the course of this pressure range the compound undergoes a phase transition between 0.58 GPa and 1.26 GPa, yielding NiAsp-II. Both polymorphs are orthorhombic, P2 12121, and feature 1D chains of Asp-Ni-Asp moieties. During the transition, the Ni(II) octahedra rotate, resulting in a dramatic shift in the position of the axial bonds with respect to the direction of polymer formation, and gives rise to an anisotropic compression of the unit cell dimensions.


McMahon M.I.,Center for Science at Extreme Conditions
Journal of Synchrotron Radiation | Year: 2014

The advent of the ESRF, APS and SPring-8 third-generation synchrotron sources in the mid-1990s heralded a golden age of high-pressure X-ray science. The high-energy monochromatic micro-focused X-ray beams from these storage rings, combined with the new high-pressure diffraction and spectroscopy techniques developed in the late 1980s, meant that researchers were immediately able to make detailed structural studies at pressures comparable with those at the centre of the Earth, studies that were simply not possible only five years previously. And new techniques, such as X-ray inelastic scattering and X-ray nuclear scattering, became possible at high pressure for the first time, providing wholly-new insight into the behaviour of materials at high densities. The arrival of new diffraction-limited storage rings, with their much greater brightness, and ability to achieve focal-spot diameters for high-energy X-ray beams of below 1μm, offers the possibility of a new generation of high-pressure science, both extending the scope of what is already possible, and also opening ways to wholly-new areas of investigation. © 2014 International Union of Crystallography.


Gould J.A.,University of Liverpool | Rosseinsky M.J.,University of Liverpool | Moggach S.A.,Center for Science at Extreme Conditions
Dalton Transactions | Year: 2012

Application of pressure on the Cu-complex CuAsp causes Jahn-Teller Cu-O bonds to be compressed, increasing the coordination environment from [4 + 1] to [4 + 2], highlighted by a discontinuity on compression of these bonding interactions. © 2012 The Royal Society of Chemistry.


Graham A.J.,Center for Science at Extreme Conditions | Tan J.-C.,University of Cambridge | Allan D.R.,Diamond Light Source | Moggach S.A.,Center for Science at Extreme Conditions
Chemical Communications | Year: 2012

Here we present detailed structural data on the effect of high pressure on Cu-btc. Application of pressure causes solvent to be squeezed into the pores until a phase transition occurs, driven by the sudden compression and expansion of equatorial and axial Cu-O bonds. © 2012 The Royal Society of Chemistry.


Whitley W.,Center for Science at Extreme Conditions | Stock C.,Center for Science at Extreme Conditions | Huxley A.D.,Center for Science at Extreme Conditions
Journal of Applied Crystallography | Year: 2015

Although CCD X-ray detectors can be faster to use, their large-area versions can be much more expensive than similarly sized photographic plate detectors. When indexing X-ray diffraction patterns, large-area detectors can prove very advantageous as they provide more spots, which makes fitting an orientation easier. On the other hand, when looking for single crystals in a polycrystalline sample, the speed of CCD detectors is more useful. A new setup is described here which overcomes some of the limitations of limited-range CCD detectors to make them more useful for indexing, whilst at the same time making it much quicker to find single crystals within a larger polycrystalline structure. This was done by combining a CCD detector with a six-axis goniometer, allowing the compilation of images from different angles into a wide-angled image. Automated scans along the sample were coupled with image processing techniques to produce grain maps, which can then be used to provide a strategy to extract single crystals from a polycrystal.


PubMed | Center for Science at Extreme Conditions
Type: Journal Article | Journal: Journal of applied crystallography | Year: 2015

Although CCD X-ray detectors can be faster to use, their large-area versions can be much more expensive than similarly sized photographic plate detectors. When indexing X-ray diffraction patterns, large-area detectors can prove very advantageous as they provide more spots, which makes fitting an orientation easier. On the other hand, when looking for single crystals in a polycrystalline sample, the speed of CCD detectors is more useful. A new setup is described here which overcomes some of the limitations of limited-range CCD detectors to make them more useful for indexing, whilst at the same time making it much quicker to find single crystals within a larger polycrystalline structure. This was done by combining a CCD detector with a six-axis goniometer, allowing the compilation of images from different angles into a wide-angled image. Automated scans along the sample were coupled with image processing techniques to produce grain maps, which can then be used to provide a strategy to extract single crystals from a polycrystal.

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