A positive temperature coefficient is the term which has been used to indicate that an increase in solubility occurs as the temperature is raised, whereas a negative coefficient indicates a decrease in solubility with rise in temperature.

Effect of Temperature

The amount of data collected during synchrotron X-ray diffraction (XRD) experiments is constantly increasing. Most of the time, the data are collected with image detectors, which necessitates the use of image reduction/integration routines to extract structural information from measured XRD patterns. This step turns out to be a bottleneck in the data processing procedure due to a lack of suitable software packages. In particular, fast-running synchrotron experiments require online data reduction and analysis in real time so that experimental parameters can be adjusted interactively. Dioptas is a Python-based program for on-the-fly data processing and exploration of two-dimensional X-ray diffraction area detector data, specifically designed for the large amount of data collected at XRD beamlines at synchrotrons. Its fast data reduction algorithm and graphical data exploration capabilities make it ideal for online data processing during XRD experiments and batch post-processing of large numbers of images.

DIOPTAS: a program for reduction of two-dimensional X-ray diffraction data and data exploration

Advances in the accuracy and efficiency of first-principles electronic structure calculations have allowed detailed studies of the energetics of materials under high pressures. At the same time, improvements in the resolution of powder x-ray diffraction experiments and more sophisticated methods of data analysis have revealed the existence of many new and unexpected high-pressure phases. The most complete set of theoretical and experimental data obtained to date is for the group-IVA elements and the group-IIIA--VA and IIB--VIA compounds. Here the authors review the currently known structures and high-pressure behavior of these materials and the theoretical work that has been done on them. The capabilities of modern first-principles methods are illustrated by a full comparison with the experimental data.

/pdf/high-pressure-phases-of-group-iv-iii-v-and-ii-vi-compounds-4wptdc31z8.pdf

High-pressure phases of group-IV, III–V, and II–VI compounds

http://people.earth.yale.edu/sites/default/files/herzberg10.pdf

Thermal history of the Earth and its petrological expression

The exchange-correlation functionals of the generalized gradient approximation (GGA) are still the most used for the calculations of the geometry and electronic structure of solids. The PBE functional [J. P. Perdew et al., Phys. Rev. Lett. 77, 3865 (1996)], the most common of them, provides excellent results in many cases. However, very recently other GGA functionals have been proposed and compete in accuracy with the PBE functional, in particular for the structure of solids. We have tested these GGA functionals, as well as the local-density approximation (LDA) and TPSS (meta-GGA approximation) functionals, on a large set of solids using an accurate implementation of the Kohn-Sham equations, namely, the full-potential linearized augmented plane-wave and local orbitals method. Often these recently proposed GGA functionals lead to improvement over LDA and PBE, but unfortunately none of them can be considered as good for all investigated solids.

/pdf/calculation-of-the-lattice-constant-of-solids-with-semilocal-47and4fs7z.pdf

Calculation of the lattice constant of solids with semilocal functionals

Partitioning of Ru, Rh, Pd, Re, Ir, and Au between Cr-bearing spinel, olivine, pyroxene and silicate melts

High pressure metal–silicate partitioning of Ni, Co, V, Cr, Si, and O

Natural olivine with 12 mol % Fe2SiO4 and synthetic orthopyroxenes with 20% and 40% FeSiO3 were studied beyond the pressure–temperature conditions of the core–mantle boundary. All samples were found to convert entirely or partially into the CaIrO3 postperovskite structure, which was recently reported for pure MgSiO3. The incorporation of Fe greatly reduces the pressure needed for the transition and establishes the new phase as the major component of the D″ layer. With the liquid core as an unlimited reservoir of iron, core–mantle reactions could further enrich the iron content in this phase and explain the intriguing seismic signatures observed in the D″ layer.

https://www.pnas.org/content/pnas/101/45/15867.full.pdf

Ferromagnesian postperovskite silicates in the D″ layer of the Earth

Platinum group element geochemistry of komatiites from the Alexo and Pyke Hill areas, Ontario, Canada

We have investigated the phase relations in the iron-rich portion of the iron-silicon (Fe-Si) alloys at high pressures and temperatures. Our study indicates that Si alloyed with Fe can stabilize the body-centered cubic (bcc) phase up to at least 84 gigapascals (compared to approximately 10 gigapascals for pure Fe) and 2400 kelvin. Earth's inner core may be composed of hexagonal close-packed (hcp) Fe with up to 4 weight percent Si, but it is also conceivable that the inner core could be a mixture of a Si-rich bcc phase and a Si-poor hcp phase.

/pdf/iron-silicon-alloy-in-earth-s-core-55zirtdyj0.pdf

Andrew J. Campbell

Papers

Partitioning of Ru, Rh, Pd, Re, Ir, and Au between Cr-bearing spinel, olivine, pyroxene and silicate melts

High pressure metal–silicate partitioning of Ni, Co, V, Cr, Si, and O

Ferromagnesian postperovskite silicates in the D″ layer of the Earth

Platinum group element geochemistry of komatiites from the Alexo and Pyke Hill areas, Ontario, Canada

Iron-silicon alloy in Earth's core?