Document Detail

Density-driven structural transformations in network forming glasses: a high-pressure neutron diffraction study of GeO(2) glass up to 17.5 GPa.
MedLine Citation:
PMID:  22951604     Owner:  NLM     Status:  Publisher    
The structure of GeO(2) glass was investigated at pressures up to 17.5(5) GPa using in situ time-of-flight neutron diffraction with a Paris-Edinburgh press employing sintered diamond anvils. A new methodology and data correction procedure were developed, enabling a reliable measurement of structure factors that are largely free from diamond Bragg peaks. Calibration curves, which are important for neutron diffraction work on disordered materials, were constructed for pressure as a function of applied load for both single and double toroid anvil geometries. The diffraction data are compared to new molecular-dynamics simulations made using transferrable interaction potentials that include dipole-polarization effects. The results, when taken together with those from other experimental methods, are consistent with four densification mechanisms. The first, at pressures up to  ≃ 5 GPa, is associated with a reorganization of GeO(4) units. The second, extending over the range from  ≃ 5 to 10 GPa, corresponds to a regime where GeO(4) units are replaced predominantly by GeO(5) units. In the third, as the pressure increases beyond ∼10 GPa, appreciable concentrations of GeO(6) units begin to form and there is a decrease in the rate of change of the intermediate-range order as measured by the pressure dependence of the position of the first sharp diffraction peak. In the fourth, at about 30 GPa, the transformation to a predominantly octahedral glass is achieved and further densification proceeds via compression of the Ge-O bonds. The observed changes in the measured diffraction patterns for GeO(2) occur at similar dimensionless number densities to those found for SiO(2), indicating similar densification mechanisms for both glasses. This implies a regime from about 15 to 24 GPa where SiO(4) units are replaced predominantly by SiO(5) units, and a regime beyond ∼24 GPa where appreciable concentrations of SiO(6) units begin to form.
Philip S Salmon; James W E Drewitt; Dean A J Whittaker; Anita Zeidler; Kamil Wezka; Craig L Bull; Matthew G Tucker; Martin C Wilding; Malcolm Guthrie; Dario Marrocchelli
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-9-06
Journal Detail:
Title:  Journal of physics. Condensed matter : an Institute of Physics journal     Volume:  24     ISSN:  1361-648X     ISO Abbreviation:  J Phys Condens Matter     Publication Date:  2012 Sep 
Date Detail:
Created Date:  2012-9-6     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  101165248     Medline TA:  J Phys Condens Matter     Country:  -    
Other Details:
Languages:  ENG     Pagination:  415102     Citation Subset:  -    
Department of Physics, University of Bath, Bath BA2 7AY, UK.
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