Original paper

The high-pressure behaviour of the "moganite" polymorph of SiO2

Léger, Jean-Michel; Haines, Julian; Chateau, Christian

Abstract

The high-pressure behaviour of the ''moganite'' polymorph of SiO2 has been investigated by angle-dispersive, X-ray powder diffraction in a diamond anvil cell at room temperature. The bulk modulus was calculated from the P-V data: B0 = 32.2 (3) GPa with B'0fixed to 5.2 as for quartz. The molar volume of moganite becomes lower than the volume of quartz above 5 GPa. Pressure-induced amorphisation occurred progressively; it was complete above 25 GPa. Upon decompression, amorphisation was partially reversible if the maximum pressure reached was below 25-30 GPa and irreversible when the pressure reached was above 45 GPa. The pressure-induced amorphisation of the quartz and moganite polymorphs of silica and phosphorus oxynitride PON, a silica analogue, is related to the distortion of the tetrahedra and, in the case of silica, to the presence of a much denser phase, in which the cation has a higher coordination number.

Keywords

silicamoganitehigh pressurex-ray diffractiondiamond anvil cell