A class of new high-pressure silica polymorphs

Details A class of new high-pressure silica polymorphs A class of new high-pressure silica polymorphs

Jun 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004pepi..143..231d&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 143, p. 231-240.

Physics

10

Scientific paper

We synthesised a number of new metastable silica modifications in the electrically heated diamond anvil cells (DACs) at pressures over 100GPa and temperatures over 1200K. Our studies reveal the existence of a new class of silica phases with different degree of the ordering of silicon atoms. Silica polymorphs with octahedrally co-ordinated silicon known so far (stishovite, fully disordered phase with niccolite-type structure, α-PbO2-type, and monoclinic (P21/c space group) post-quartz phase) are members of this class. The details of the silicon distribution among free positions in the oxygen network strongly depend on the starting material and the conditions of high-pressure high-temperature treatment of silica, but a general trend is that at pressures above 40-45GPa most of the silicon atoms are placed in octahedral positions. Our structural model provides a key for an explanation of the mysterious behaviour of silica, known for more than 30 years, when at the same pressure and temperature range different phases were synthesised.

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