Stability limits and transformation pathways ofα-quartz under high pressure

Abstract

Ubiquitous on Earth, α-quartz plays an important role in modern science and technology. However, despite extensive research in the past, the mechanism of the polymorphic transitions of α-quartz at high pressures remains poorly understood. Here, combining in situ single-crystal xray diffraction experiment and advanced ab initio modeling, we report two stability limits and competing transition pathways of α-quartz under high pressure. Under near-equilibrium compression conditions at room temperature, α-quartz transits to a new P2/c silica phase, via a structural intermediate. If the thermally activated transition is kinetically suppressed, the ultimate stability of α-quartz is controlled by its phonon instability and α-quartz collapses into a different crystalline phase. Our studies reveal that pressure-induced solid-state transformation of α-quartz undergoes a succession of structural stability limits due to thermodynamic and mechanical catastrophes, and exhibits a hierarchy of transition pathways contingent upon kinetic conditions.

Experimental and first-principles calculation study of the pressure-induced transitions to a metastable phase inGaPO4and in the solid solutionAlPO4−Angot1, Huang2, Levelut3 et al. 2017Phys. Rev. Materials3100View full textAdd to dashboardCite

“…be less reconstructive than the berlinite-CrVO 4 transition. This is similar to what occurs in α-quartz, where at ambient temperature transitions occur to metastable monoclinic P 2 1 /c and P 2/c phases [2,46] via diffusionless pathways [47]. As the phase is metastable, its presence in a given experiment will depend on time (transition kinetics), temperature (in the absence of enough thermal activation to obtain the stable high-pressure form), and nonhydrostatic stress, which could favor certain energetic pathways.…”

Percolation transitions in compressed SiO2 glasses

“…With increasing pressure, two more percolating clusters appear at 10 GPa and coexist with the first one: one built up by connected SiO 5 -SiO 5 pentahedra and the second by connected SiO 5 -SiO 6 polyhedra. The percolating cluster structures containing a mixture of SiO 4 and SiO 5 between 8 and 10 GPa, as well SiO 6 between 10 and 13 GPa, recall the pressure-induced post-quartz amorphous phases reported previously [31,32]. Then, at 13 GPa, a (SiO 6 -SiO 6 ) ∞ cluster appears and percolates.…”

“…Finally, Extended Data Table 1 gives the densities of the crystalline polymorphs and indicate the corresponding pressure ranges [6,31,51,52]. The comparison with the corresponding polyamorph phases of v-SiO 2 is striking.…”

Structural response of α-quartz under plate-impact shock compression

“…The pathways between structures can be broken down into sets of transformations involving some combinations of displacive and ordering mechanisms. In recent years, new studies have revisited this subject with various phenomenological approaches including excited-state transition pathway calculations and ab initio molecular dynamics ( 9 , 10 , 30 ). These simulations suggest that under nonhydrostatic conditions, the quasi–body-centered cubic oxygen sublattice that describes α-quartz can transform via a martensitic mechanism (Burgers path) to an hcp oxygen lattice ( 9 , 38 ).…”