HR: 10:35h
AN: V41E-02    [PDF]
TI: Pressure induced structural changes in amorphous silicates
AU: * Prakapenka, V B
EM: prakapenka@cars.uchicago.edu
AF: GSECARS, University of Chicago, 5640 S. Ellis Ave., Chicago, IL 60637 United States
AU: Shen, G
EM: shen@cars.uchicago.edu
AF: GSECARS, University of Chicago, 5640 S. Ellis Ave., Chicago, IL 60637 United States
AU: Rivers, M L
EM: rivers@cars.uchicago.edu
AF: GSECARS, University of Chicago, 5640 S. Ellis Ave., Chicago, IL 60637 United States
AU: Sutton, S R
EM: sutton@cars.uchicago.edu
AF: GSECARS, University of Chicago, 5640 S. Ellis Ave., Chicago, IL 60637 United States
AB: The study of amorphous structures provides a basis for understanding the chemical-physical properties of glass and liquid materials at extreme conditions. However, there are only a few experimental reports available characterizing amorphous silicates at high pressures. The main reason for limited experimental studies is related to the weak scattering of non-crystalline silicates in the small pressure chamber of the diamond anvil cell (DAC) and the associated small accessible 2-theta range. In this work, we have used a modified DAC with x-ray transparent cubic BN seats that results in a maximum momentum transfer above 110 nm$^{-1}$. The diffraction patterns were collected in full solid angle using an on-line imaging plate detector and brilliant, high energy (37.44 keV) synchrotron x-radiation at GSECARS undulator beamline (APS). For background corrections we recorded x-ray scattering patterns from an empty cell (without sample, but at the same position and conditions used for high pressure data collection). The high pressure behavior (compress/decompress) of amorphous SiO$_{2}$ and MgSiO$_{3}$ was studied up to 70 GPa with steps of $\sim$5 GPa at room temperature. The starting materials were synthesized by a sol-gel technique, which allows the formation of highly disordered polymer-like three-dimensional matrices where silicon/magnesium atoms are bonded to oxygen atoms in an irregular non-crystalline network. For both SiO$_{2}$ and MgSiO$_{3}$, we have observed clear pressure-induced structural changes rather than isotropic contraction. On decompression, reversible structural behavior was found for both silicates. The observed structural changes in the medium-range order of the amorphous network and the kinetics of this process in SiO$_{2}$ and MgSiO$_{3}$ provide a basis for understanding the dynamical properties of high-density non-crystalline materials at extreme conditions.
DE: 3924 High-pressure behavior
DE: 3954 X ray, neutron, and electron spectroscopy and diffraction
DE: 5112 Microstructure
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting