Ian G. Wood's research while affiliated with University College London and other places
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Publications (244)
Experimental and computational studies of ammonium carbamate have been carried out, with the objective of studying the elastic anisotropy of the framework manifested in (i) the thermal expansion and (ii) the compressibility; furthermore, the relative thermodynamic stability of the two known polymorphs has been evaluated computationally. Using high-...
The MgGeO3 system is a low-pressure analog for the Earth-forming (Mg,Fe)SiO3 system and exhibits recoverable orthopyroxene, clinopyroxene, and ilmenite structures below 6 GPa. The pressure-temperature conditions of the clinopyroxene to ilmenite phase transition are reasonably consistent between studies, having a positive Clapeyron slope and occurri...
Hydrous Fo91 ringwoodite crystals were synthesized at 20 GPa and high-temperature conditions using a multi-anvil press. Recovered crystals were analyzed using electron microprobe analysis, Raman spectroscopy, infrared spectroscopy, synchrotron Mössbauer spectroscopy, single-crystal X-ray diffraction, and single-crystal Laue neutron diffraction, to...
Si and C are cosmochemically abundant elements soluble in hcp Fe under pressure and temperature and could therefore be present in the Earth's inner core. While recent ab initio calculations suggest that the observed inner core density and velocities could be matched by an Fe‐C‐Si alloy, the combined effect of these two elements has only recently st...
The lowermost portion of Earth's mantle (D″) above the core-mantle boundary shows anomalous seismic features, such as strong seismic anisotropy, related to the properties of the main mineral MgSiO3 postperovskite. But, after over a decade of investigations, the seismic observations still cannot be explained simply by flow models which assume disloc...
The regime governing the growth of Mercury's core is unknown, but the dynamics of core growth are vital to understanding the origin and properties of the planet's weak magnetic field. Here, we use advanced first-principles methods, which include a magnetic entropy contribution, to investigate the magnetic and thermo-elastic properties of liquid Fe-...
![Lattice and diffraction peak parameters for CaSiO3 and Ca[Si0.6Ti0.4]O3...](publication/335174582/figure/fig1/AS:792027428044803@1565845462681/Lattice-and-diffraction-peak-parameters-for-CaSiO3-and-CaSi06Ti04O3-perovskite-a-d_Q320.jpg)
![Refined X-ray diffraction patterns from Ca[Si0.6Ti0.4]O3...](publication/335174582/figure/fig3/AS:792027428044804@1565845462904/Refined-X-ray-diffraction-patterns-from-CaSi06Ti04O3-perovskite-a-c-Rietveld_Q320.jpg)
![X-ray diffraction patterns from Ca[Si0.6Ti0.4]O3 perovskite
a, Complete...](publication/335174582/figure/fig4/AS:792027432239104@1565845463009/X-ray-diffraction-patterns-from-CaSi06Ti04O3-perovskite-a-Complete-diffraction_Q320.jpg)
Seismology records the presence of various heterogeneities throughout the lower mantle1,2, but the origins of these signals—whether thermal or chemical—remain uncertain, and therefore much of the information that they hold about the nature of the deep Earth is obscured. Accurate interpretation of observed seismic velocities requires knowledge of th...
Since being discovered initially in mixed-cation systems, a method of forming end-member NiSO4·9H2O and NiSO4·8H2O has been found. We have obtained powder diffraction data from protonated analogues (with X-rays) and deuterated analogues (using neutrons) of these compounds over a range of temperatures, allowing us to determine their crystal structur...
An apparatus is described for the compression of samples to ∼2 GPa at temperatures from 80 to 300 K, rapid chilling to 80 K whilst under load and subsequent recovery into liquid nitrogen after the load is released. In this way, a variety of quenchable high-pressure phases of many materials may be preserved for examination outside the high-pressure...
A low-temperature stage for X-ray powder diffraction in Bragg–Brentano reflection geometry is described. The temperature range covered is 40–315 K, with a temperature stability at the sample within ±0.1 K of the set point. The stage operates by means of a Gifford–McMahon (GM) closed-cycle He refrigerator; it requires no refrigerants and so can run...
ABF3 compounds have been found to make valuable low-pressure analogues for high-pressure silicate phases that are present in the Earth’s deep interior and that may also occur in the interiors of exoplanets. The phase diagrams of two of these materials, KCaF3 and NaMgF3, have been investigated in detail by static ab initio computer simulations based...
On the basis of ab initio computer simulations, pre-melting phenomena have been suggested to occur in the elastic properties of hexagonal close-packed iron under the conditions of the Earth’s inner core just before melting. The extent to which these pre-melting effects might also occur in the physical properties of face-centred cubic metals has bee...
We describe the capability to measure high-resolution neutron powder diffraction data to a pressure of at least 8 kbar. We have used the HRPD instrument at the ISIS neutron source and a piston-cylinder design of pressure cell machined from a null-scattering titanium zirconium alloy. Data were collected under hydrostatic conditions from an elpasolit...
We have measured the thermal expansion of (Fe1-y Ni y )Si for y = 0, 0.1 and 0.2, between 40 and 1273 K. Above ~700 K the unit-cell volumes of the samples decrease approximately linearly with increasing Ni content. Below ~200 K the unit-cell volume of FeSi falls to a value between that of (Fe0.9Ni0.1)Si and (Fe0.8Ni0.2)Si. We attribute this extra c...
The Fe–Ni–Si system is potentially a very important component of terrestrial planetary cores. However, at present, even the behaviour of the FeSi and NiSi end members is poorly understood, especially at low to moderate pressures—the data for FeSi are contradictory and NiSi has been little studied. For FeSi, there is general agreement that there is...
We have measured the thermal expansion of (Fe<sub>1- y </sub>Ni<sub> y </sub>)Si for y = 0, 0.1 and 0.2, between 40 and 1273 K. Above ∽700 K the unit-cell volumes of the samples decrease approximately linearly with increasing Ni content. Below ∽200 K the unit-cell volume of FeSi falls to a value between that of (Fe<sub>0.9</sub>Ni<sub>0.1</sub>)Si...
Since being discovered initially in mixed-cation systems, a method of forming end-member MgSO4·9H2O has been found. We have obtained powder diffraction data from protonated analogues (using X-rays) and deuterated analogues (using neutrons) of this compound over a range of temperatures and pressures. From these data we have determined the crystal st...
We have collected neutron powder diffraction data from MgSO 4 ·11D 2 O (the deuterated analogue of meridianiite), a highly hydrated sulfate salt that is thought to be a candidate rock-forming mineral in some icy satellites of the outer solar system. Our measurements, made using the PEARL/HiPr and OSIRIS instruments at the ISIS neutron spallation so...
Since being discovered initially in mixed-cation systems, a method of forming end-member MgSO 4 ·9H 2 O has been found. We have obtained powder diffraction data from protonated analogues (using X-rays) and deuterated analogues (using neutrons) of this compound over a range of temperatures and pressures. From these data we have determined the crysta...
We have grown single crystals of M²⁺SO4 hydrates at 270 K from aqueous solutions in the ternary systems CoSO4–MgSO4–H2O and MnSO4–MgSO4–H2O. These systems exhibit broad stability fields for a triclinic undecahydrate on the Mg-rich side (i.e., Co- or Mn-bearing meridianiite solid solutions) and stability fields for monoclinic heptahydrates on the Mg...
The phase diagram of NiSi has been determined using in situ synchrotron X-ray powder diffraction multi-anvil experiments to 19 GPa, with further preliminary results in the laser-heated diamond cell reported to 60 GPa. The low-pressure MnP-structured phase transforms to two different high-pressure phases depending on the temperature: the ε-FeSi stru...
The density of the Earth's inner core is less than that of pure iron and the P-wave velocities and, particularly, the S-wave velocities in the inner core observed from seismology are lower than those generally obtained from mineral physics. On the basis of measurements of compressional sound velocities to ∼100 GPa in diamond-anvil cells, extrapolat...
Single crystals of glycine zinc sulfate pentahydrate [systematic name: hexaaquazinc tetraaqua-diglycine zinc bissulfate], [Zn(H 2 O) 6 ][Zn(H 2 O) 2 (C 2 H 5 NO 2 ) 2 ](SO 4 ) 2 , have been grown by isothermal evaporation from aqueous solution at room temperature and characterized by single-crystal neutron diffraction. The unit cell contains two un...
It has recently been reported, on the basis of extrapolated experimental data, that the iron carbide, Fe7C3, has shear wave velocities and a Poisson's ratio consistent with the seismological values for the Earth's inner core, and thus that Fe7C3 is a strong candidate for the inner core composition. In this study, using ab initio molecular dynamics...
We have identified a new compound in the glycine–MgSO
4
–water ternary system, namely glycine magnesium sulfate trihydrate (or Gly·MgSO
4
·3H
2
O) {systematic name:
catena
-poly[[tetraaquamagnesium(II)]-μ-glycine-κ
2
O
:
O
′-[diaquabis(sulfato-κ
O
)magnesium(II)]-μ-glycine-κ
2
O
:
O
′]; [Mg(SO
4
)(C
2
D
5
NO
2
)(D
2
O)
3
]
n
}, which can be grown...
The equation of state of the orthorhombic phase of NiSi with
Pmmn
symmetry has been determined at room temperature from synchrotron-based X-ray diffraction measurements of its lattice parameters, made in a diamond anvil cell. Measurements were performed up to 44 GPa, using Ne as the pressure medium and Au as the pressure standard. The resulting pre...
The agreement between shear wave velocities for the Earth's inner core observed from seismology with those derived from mineral physics is considerably worse than for any other region of the Earth. Furthermore, there is still debate as to the phase of iron present in the inner core, particularly when alloying with nickel and light elements is taken...
The melting curve of Ni has been determined to 125 GPa using laser-heated diamond anvil cell (LH-DAC) experiments in which two melting criteria were used: firstly, the appearance of liquid diffuse scattering (LDS) during in situ X-ray diffraction (XRD) and secondly, plateaux in temperature vs. laser power functions in both in situ and off-line expe...
Using the recently upgraded Polaris diffractometer at the ISIS Spallation Neutron Source (Rutherford Appleton Laboratory), the crystal structures of the post-perovskite polymorphs of NaCoF3 and NaNiF3 have been determined by time-of-flight neutron powder diffraction from samples, of mass 56 and 16 mg, respectively, recovered after synthesis at ∼20...