28 research outputs found
Compressibility and Electronic Structure of MgB2 up to 8 GPa
The lattice parameters of MgB2 up to pressures of 8 GPa were determined using
high-resolution x-ray powder diffraction in a diamond anvil cell. The bulk
modulus, B0, was determined to be 151 +-5 GPa. Both experimental and
first-principles calculations indicate nearly isotropic mechanical behavior
under pressure. This small anisotropy is in contrast to the 2 dimensional
nature of the boron pi states. The pressure dependence of the density of states
at the Fermi level and a reasonable value for the average phonon frequency
account within the context of BCS theory for the reduction of Tc under
pressure.Comment: REVTeX file. 4 pages, 4 figure
Structure and Dynamics of Liquid Iron under Earth's Core Conditions
First-principles molecular dynamics simulations based on density-functional
theory and the projector augmented wave (PAW) technique have been used to study
the structural and dynamical properties of liquid iron under Earth's core
conditions. As evidence for the accuracy of the techniques, we present PAW
results for a range of solid-state properties of low- and high-pressure iron,
and compare them with experimental values and the results of other
first-principles calculations. In the liquid-state simulations, we address
particular effort to the study of finite-size effects, Brillouin-zone sampling
and other sources of technical error. Results for the radial distribution
function, the diffusion coefficient and the shear viscosity are presented for a
wide range of thermodynamic states relevant to the Earth's core. Throughout
this range, liquid iron is a close-packed simple liquid with a diffusion
coefficient and viscosity similar to those of typical simple liquids under
ambient conditions.Comment: 13 pages, 8 figure
Source assemblage types for cratonic diamonds from X-ray synchrotron diffraction
Three single crystals of clinopyroxene trapped within three different gem-quality diamonds from the Udachnaya kimberlite (Siberia, Russia) were analysed in situ by single-crystal synchrotron X-ray diffraction in order to obtain information on their chemical composition and infer source assemblage type. A non-destructive approach was used with high-energy (≈ 60 keV; λ ≈ 0.206 Å) at I15, the extreme-conditions beamline at Diamond Light Source. A dedicated protocol was used to center the mineral inclusions located deep inside the diamonds in the X-ray beam. Our results reveal that two of the inclusions can be associated with peridotitic paragenesis whereas the third is eclogitic. This study also demonstrates that this non-destructive experimental approach is extremely efficient in evaluating the origin of minerals trapped in their diamond hosts.5 page(s