Hedenbergite (CaFeSi2O6) Glass under High Pressure
Abstract
The behavior of silicate melts under high-pressure and high-temperature conditions is of primary interest, both for their fundamental properties and significant roles in thermal transport and chemical differentiation in planetary interiors. Recently, considerable progress has been made in understanding structures of liquid silicates by theoretical prediction and various spectroscopic experiments, yet still many issues need to be addressed and several challenges must be overcome to improve in the understanding of silicate melts. Raman spectroscopy can probe local atomic vibrational modes, thereby providing additional structural information that cannot be obtained by X-ray diffraction. Here, we report the compression behavior of hedenbergite (CaFeSi2O6) glass up to 64 GPa in the diamond anvil cell using Raman spectroscopy. Many significant changes in Raman vibrational properties are observed. For example, the intensity of the broad Raman band around 850 to 1200 cm-1, known to represent Qn species (Si-O stretching modes) in tetrahedrally coordinated silicates, decreases with increasing pressure and completely disappears around 35 GPa, suggesting that Si-O coordination number (CN) has changed significantly from 4. The intensity of the Raman bands at 600 cm-1, which represent the Si-O-Si, O-Si-O bending modes also disappears around 20 GPa, whereas a new band begins forming near 600 cm-1 whose centroid of Raman shift increases rapidly with pressure until about 35 GPa, above which the peak position increases at a much lower pace. These vibrational property changes are in broad agreement with XRD data on SiO2 glass (Prescher et al., 2017), where rapid increase in Si-O CN begins around 20 GPa from CN=4, reaching CN=5.5 around 35 GPa, above which the increase in CN with pressure exhibits a much slower pace. Another peak appeared around 250 cm-1, above 20 GPa, in close vicinity to the boson peak around 150 cm-1. The origin of this new peak is unknown. Work is in underway to examine Raman vibrational modes in SiO2 CaSiO3 and CaMgSi2O6 glasses, which may help understand the nature of the vibrational properties of hedenbergite glass. Our result may contribute to an understanding of the structure-property relationships for silicate glasses and melts, providing important implication for the evolution of deep Earth's interiors.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMMR14A..05R
- Keywords:
-
- 3919 Equations of state;
- MINERAL PHYSICSDE: 3924 High-pressure behavior;
- MINERAL PHYSICSDE: 3954 X-ray;
- neutron;
- and electron spectroscopy and diffraction;
- MINERAL PHYSICSDE: 3994 Instruments and techniques;
- MINERAL PHYSICS