George Serghiou

University of Edinburgh

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R. Boehler

Oak Ridge National Laboratory

Andreas Zerr

Université Sorbonne Paris Nord

A. Chopelas

Max Planck Society

H. J. Reichmann

Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences

Monika Koch‐Müller

Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences

Peter Kroll

The University of Texas at Arlington

Oliver Tschauner

University of Nevada, Las Vegas

L. Chudinovskikh

Institute of Experimental Mineralogy

G. Miehe

Technical University of Darmstadt

Paul R. Hunter

University of East Anglia

Cooperative Institutions

University of Edinburgh

Max Planck Institute for Chemistry

Technical University of Darmstadt

Centre National de la Recherche Scientifique

Max Planck Society

Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences

Carnegie Institution for Science

Geophysical Laboratory

TU Bergakademie Freiberg

European Synchrotron Radiation Facility

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Synthesis of cubic silicon nitride

Nature (1999)

Andreas Zerr G. Miehe George Serghiou M. Schwarz Edwin Kroke

10.1038/22493

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Citations (628)

Explanation of pressure-induced transformations in chain silicates based on their modular structures

Journal of Physics Condensed Matter (2000)

George Serghiou A. Chopelas R. Boehler

Above 35 GPa tetrahedrally coordinated (SiO4) chain silicates either become amorphous or transform to dense crystalline phases that generally contain SiO6 octahedra, depending on the sequencing of their building blocks (P and C modules). Previous work shows that the P and C modules are respectively slabs of the pyroxene and CaSiO3 chain silicate structures. Chain silicates containing only P modules (e.g. the pyroxenes MgSiO3, Ca0.5Mg0.5SiO3, MnSiO3) transform to dense crystalline phases. Chain silicates containing a sequence of P and C modules (e.g. the pyroxenoid MnSiO3) become amorphous, and those containing only C modules (e.g. the pyroxenoid CaSiO3) exhibit both crystalline and amorphous regions. Amorphization is likely to be triggered by disordering of the C modules and C-P interfaces, both of which become unstable with respect to P modules and P-P interfaces upon compression. The absence of C-P interfaces may explain the existence of both crystalline and amorphous regions in chain silicates containing only C modules.

Chain (unit)

Pyroxene

10.1088/0953-8984/12/42/301

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Citations (11)

The transition of pyrope to perovskite

Physics and Chemistry of Minerals (1998)

George Serghiou Andreas Zerr A. Chopelas R. Boehler

Pyrope

Ilmenite

Hydrostatic pressure

Diamond anvil cell

10.1007/s002690050102

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Citations (20)

Phase Transitions and Material Synthesis using the CO₂‐Laser Heating Technique in a Diamond Cell

Andreas Zerr George Serghiou R. Boehler

Diamond anvil cell

10.1002/9783527618217.ch2

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Citations (15)

Four to sixfold coordination changes in crystalline silicates at high pressure

High Pressure Research (2003)

George Serghiou R. Boehler A. Chopelas

MgSiO3 exists in a variety of polymorphs which can be largely divided into two subclasses: (a) low pressure modifications in which Si is coordinated to four oxygens and (b) high pressure modifications in which Si is coordinated to six oxygens. The coordination change usually requires an accompanying high temperature. We present a four to six coordination change in MgSiO3 orthoenstatite at high pressure and ambient temperature in an argon pressure medium, using Raman spectroscopic measurements in a diamond cell. CO2 laser-heating experiments indicate that the four to sixfold coordination change is facilitated by defects in the structure which may serve as nucleation sites for the formation of the octahedrally coordinated silicate phase.

Diamond anvil cell

Ambient pressure

Coordination number

10.1080/0895795031000109689

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Citations (0)

(Mg,Fe)SiO3-Perovskite Stability and Lower Mantle Conditions

Science (1999)

George Serghiou Andreas Zerr R. Boehler

10.1126/science.285.5430.981q

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Citations (2)

Pressure-induced amorphization of wollastonite (CaSiO3) at room temperature

The Journal of Chemical Physics (1993)

George Serghiou William S. Hammack

Energy dispersive x-ray diffraction and Raman measurements show that the mineral wollastonite (CaSiO3) becomes amorphous at a pressure of 25.6 GPa at 300 K. A consideration of the high pressure/high temperature behavior of CaSiO3 shows that the amorphization occurs because the phase transition wollastonite→perovskite CaSiO3 is kinetically impeded. We suggest that the amorphous phase may be viewed as a defective long-period modulated wollastonite phase.

Wollastonite

10.1063/1.464361

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Citations (34)

Melting and homogeneity in germanium–silicon alloys and a modified micro-manufactured assembly for stable high pressure and temperature measurements

High Pressure Research (2014)

George Serghiou N. Odling Paul R. Hunter A. A. Abbie B. Armstrong

We present a modified assembly for high pressure and temperature measurements in a MAX80 press. The designs include a T-shaped power coupler with a ring-shaped insulator, a precision made, all-in-one single-piece crucible, with mirror-image located, flat-bottomed sample and pressure marker chambers, with press-fit lids and thermocouple insert in the middle of the crucible. These features facilitate assembly stability, reproducibility of in situ measurements, avoidance of chemical contamination, portability of assembly and ease of sectioning for further analysis. These attributes are important in evaluating phase relations at high pressure, especially where melting of the charge is investigated. While the cubic-diamond structured silicon–germanium system exhibits a complete solid solution, in practice, homogeneous solid solutions are not readily accessible because of the considerable difference in temperature between the liquidus and solidus and concomitant segregation coefficients. We use our designs, for in situ X-ray diffraction measurements and melting of germanium–silicon alloys at high pressure for both a germanium-rich and a silicon-rich starting composition.

Liquidus

Solidus

Thermocouple

Crucible (geodemography)

10.1080/08957959.2013.856896

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Citations (4)

Spectroscopic evidence for pressure-induced phase transitions in diopside

Physics and Chemistry of Minerals (2002)

A. Chopelas George Serghiou

Diopside

10.1007/s00269-002-0244-8

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Citations (27)

(Mg,Fe)SiO ₃ -Perovskite Stability Under Lower Mantle Conditions

Science (1998)

George Serghiou Andreas Zerr R. Boehler

In three different experiments up to 100 gigapascals and 3000 kelvin, (Mg,Fe)SiO3-perovskite, the major component of the lower mantle, remained stable and did not decompose to its component oxides (Mg, Fe)O and SiO2. Perovskite was formed from these oxides when heated in a diamond anvil cell at pressures up to 100 gigapascals. Both MgSiO3 crystals and glasses heated to 3000 kelvin at 75 gigapascals also formed perovskite as a single phase, as evident from Raman spectra. Moreover, fluorescence measurements on chromium-doped samples synthesized at these conditions gave no indication of the presence of MgO.

Diamond anvil cell

10.1126/science.280.5372.2093

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Citations (84)