The Pyrite-Type High-Pressure Form of Silica

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Science  05 Aug 2005:
Vol. 309, Issue 5736, pp. 923-925
DOI: 10.1126/science.1114879

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Silica (SiO2) exhibits extensive polymorphism at elevated pressures. X-ray diffraction measurements showed that a high-pressure form with a pyrite-type structure, denser than other known silica phases, is stable above 268 giga-pascals and 1800 kelvin. The silicon coordination number increases from 6 in the α-PbO2-type phase to 6+2 in the pyrite-type phase, leading to a large increase in density by about 5% at the phase transition.

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