COLLOQUIUM OF THE COMPUTATIONAL MATERIALS SCIENCE CENTER – QINGYANG HU – NEW TRANSITORY PHASES OF SILICA UNDER HIGH PRESSURE
COLLOQUIUM OF THE COMPUTATIONAL MATERIALS SCIENCE CENTER
AND THE DEPARTMENT OF COMPUTATIONAL AND DATA SCIENCES
(CSI 898-Sec 001)
NEW TRANSITORY PHASES OF SILICA UNDER HIGH PRESSURE
Carnegie Institution of Washington
Silica is one of the most-abundant natural compounds and a major component of the Earth’s crust and mantle. Its various high-pressure forms make it an often-used study subject for scientists interested in the transition between different chemical phases under extreme conditions, such as those mimicking the deep Earth. Compressing single crystal coesite SiO2 under hydrostatic pressures of 26~53 gigapascal at room temperature, we discover a new polymorphic phase transition mechanism of coesite to post-stishovite, by means of single-crystal synchrotron x-ray diffraction experiment and first-principles computational modeling.
The transition features the formation of multiple previously unknown triclinic phases of SiO2 on the transition pathway as structural intermediates. Coexistence of the low-symmetry phases results in extensive splitting of the original coesite X-ray diffraction peaks that appear as dramatic peak broadening and weakening, resembling an amorphous material. This work provides new insights into the structural transition of SiO2 crystal under high pressures, and clarifies the issue of the pressure-induced amorphization of coesite, which has often been cited as an archetypal example of the amorphization phenomena in general.
November 2, 2015 – 4:30 p.m.
Exploratory Hall, Room 3301
Refreshments will be served at 4:15 PM.
Find the schedule at http://www.cmasc.gmu.edu/seminars.htm