The pressure-induced phase transition(s) of ZrSiO4: revised: Experimental proof for the existence of a new high-pressure polymorph of zircon
Abstract
The existence of a new high-pressure low-symmetry (HPLS) ZrSiO4 phase (space group I4¯2d), which has been predicted by density-functional-theory (DFT) calculations (Stangarone et al. in Am Mineral, 2019b), is experimentally confirmed by in situ high-pressure Raman spectroscopic analysis up to 25.3 GPa. The new ZrSiO4 polymorph is developed from zircon via a soft-mode-driven displacive phase transition. The Cochran-law-type pressure dependency of the soft-mode wavenumber reveals a zircon-to-HPLS critical pressure pc = 20.98 ± 0.02 GPa. The increase in the phonon compressibilities of the zircon hard mode near 202cm-1 at p>pr=10.0 GPa as well as of the reidite hard mode near 349cm-1 at p<pr marks the pressure above which zircon becomes thermodynamically metastable with respect to reidite; the experimentally determined value of pr is in good accordance with the equilibrium zircon-reidite transition pressure derived from DFT simulations. However, at room temperature, there is not enough driving force to rebuild the atomic linkages and the reconstructive transition to reidite happens ∼ 1.4 GPa above pc, indicating that at room temperature, the HPLS phase is a structural bridge between zircon and reidite. The pressure dependencies of the phonon modes in the range 350--460cm-1 reveal that the reconstructive phase transition in the ZrSiO4 system is triggered by energy resonance and admixture of hard modes from the parent and resultant phase.
- Publication:
-
Physics and Chemistry of Minerals
- Pub Date:
- September 2019
- DOI:
- 10.1007/s00269-019-01041-1
- Bibcode:
- 2019PCM....46..807M
- Keywords:
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- Zircon;
- High pressure;
- Phase transition;
- Raman spectroscopy;
- Soft mode