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Establishing the structure of GeS2 at high pressures and temperatures: a combined approach using x-ray and neutron diffraction

DOI: 10.1088/0953-8984/21/47/474217 DOI Help

Authors: Anita Zeidler (University of Bath) , James Drewitt (University of Bath) , Philip Salmon (University of Bath) , Adrian Barnes (HH Wills Phys Lab, Bristol) , Wilson Crichton (ESRF) , Stefan Klotz (Univresity of Paris) , Henry Fischer (Inst Max Von Laue Paul Langevin) , Chris Benmore (Argonne National Laboratory) , Silvia Ramos (Diamond Light Source) , Alex Hannon (ISIS)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Physics: Condensed Matter , VOL 21 (47) , PAGES 474217

State: Published (Approved)
Published: November 2009

Abstract: The change in structure of glassy GeS2 with pressure increasing to {\simeq }5~\mathrm {GPa} at ambient temperature was explored by using in situ neutron and x-ray diffraction. Under ambient conditions, the glass structure is made from a mixture of corner- and edge-sharing Ge(S1/2)4 tetrahedra where 47(5)% of the Ge atoms are involved in edge-sharing configurations. The network formed by these tetrahedra orders on an intermediate range as manifested by the appearance of a pronounced first sharp diffraction peak in the measured total structure factors at a scattering vector k = 1.02(2) Å−1 which has a large contribution from Ge–Ge correlations. The intermediate range order breaks down when the pressure on the glass increases above ≈2 GPa but there does not appear to be a significant alteration of the Ge–S coordination number or corresponding bond length with increasing density. The results for the glass are consistent with a densification mechanism in which there is a replacement of edge-sharing by corner-sharing Ge centred tetrahedral motifs and/or a reduction in the Ge–\hat {\mathrm {S}} –Ge bond angle between corner-sharing tetrahedral motifs with increasing pressure. The change in structure with increasing temperature at a pressure of {\simeq }5~\mathrm {GPa} was also investigated by means of in situ x-ray diffraction as the glass crystallized and then liquefied. At 5.2(1) GPa and 828(50) K the system forms a tetragonal crystal, with space group I\bar {4}2d and cell parameters a = b = 4.97704(12) and c = 9.5355(4) Å, wherein corner-sharing Ge(S1/2)4 tetrahedra pack to form a dense three-dimensional network. A method is described for correcting x-ray diffraction data taken in situ under high pressure, high temperature conditions for a cylindrical sample, container and gasket geometry with a parallel incident beam and with a scattered beam that is defined using an oscillating radial collimator. A method is also outlined for obtaining coordination numbers from direct integration of the peaks in measured x-ray total pair distribution functions.

Journal Keywords: Ambient Temperature; Beams; Bond Angle; Bond Lengths; Collimators; Containers; Coordination Number; Crystallization; Cylindrical Configuration; Distribution Functions; Gaskets; Germanium; Germanium Sulfides; Glass; Neutron Diffraction; Pressure Range Giga Pa; Pressure Range Mega Pa 10-100; Space Groups; Structure Factors; Sulfur; Temperature Range 0400-1000 K; Three-Dimensional Calculations; X-Ray Diffraction

Subject Areas: Physics


Instruments: NONE-No attached Diamond beamline

Added On: 30/11/2009 08:31

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