Infrared absorption spectra of the high-pressure phases of cristobalite and their coordination numbers of silicon atoms

New description of structural disorder in silica glass. II. Application of atomistic energy distribution analysis to pressure effects

“…For cristobalite, our study supports the idea that the structural transformation that occurs between 19 and 20 GPa is not pressureinduced amorphization, but a crystal-crystal transition, as has been hitherto discussed [12][13][14][15][16]. In contrast to the case of quartz, the AED functions of cristobalite at 30 GPa are still sharp, as shown in Fig.…”

“…Two additional transitions to cristobalite III and IV (according to Hemley's consistent nomenclature [1]) have been reported at 10 and 35 GPa [14]. Studies by Raman [12] and infrared [13] spectroscopy have shown that cristobalite III and IV have predominantly tetrahedral Si. On the other hand, MD calculations have predicted a new structure with mixedcoordination states [15].…”

“…The existence of a lower-symmetry phase is indicated by abrupt changes at ∼1.5 GPa in X-ray diffraction patterns and in Raman and infrared spectra [10][11][12][13], whereby a tetragonal phase (low cristobalite) transforms to a monoclinic phase, cristobalite II, as designated by Palmer et al [12]. Two additional transitions to cristobalite III and IV (according to Hemley's consistent nomenclature [1]) have been reported at 10 and 35 GPa [14].…”

Pressure-induced transformations of cristobalite

“…Close agreement in X-ray data for our quenched samples and for the samples of Tsuchida and Yagi [5] (especially taking into account the dierent methods of synthesis of the samples, dierent maximum pressures, possible dierences in decompression rates, etc. [3,6]) allows us to conclude that Cristobalite XIII [5] is the a-PbO 2 -like silica quenched from high pressure. According to the molecular dynamics calculations with semi-empirical potentials and ab initio pseudopotential calculations [11], a-PbO 2 -like silica phase belongs to Pbcn (or Pnca in another setting) space group.…”

“…At pressures above 10 GPa, ®rst Tsuchida and Yagi [5] and later other groups [3,4,6] reported about a phase transition to one more phase (Cristobalite XI according to [5] or Cristobalite III according to [7]). Under further compression at pressures above 40 GPa, Cristobalite XII [5,6] was found.…”