Optical properties of silica (SiO2) at lower mantle conditions: Implications for conductivity of molten mantle
Abstract
Silica (SiO2) is a major chemical constituent of the Earth, and its properties at high pressures and temperatures are important both for deep-earth geophysics and for studies of terrestrial impact events. A number of interesting phenomena, such as amorphization on static compression and the formation of microstructures on dynamic shock compression, were first experimentally observed in silica and subsequently seen in a wide variety of dielectric materials, including other planetary minerals. Here, we report experimental evidence for increased electrical conduction in molten SiO2 at extreme pressures and temperatures. Using laser-driven shock waves, two initial forms of SiO2, fused silica and alpha-quartz, were subjected to multi-Megabar pressures and temperatures of tens of thousands of Kelvin. Light at 532 nm reflected from the samples provides a measurement of the optical opacity or reflectivity of the shocked material. These measurements suggest that initially transparent silica, characterized by a wide gap between the electronic energy bands, exhibits a major increase in electrical conductivity: first, there is a discontinuous increase on melting, and then a continuous increase with temperature and pressure in the molten state, presumably in response to chemical dissociation of the SiO2. It is likely that similar behavior will be identified in other dielectric materials, including the primary constituent of the Earths mantle, MgSiO3 perovskite. These results may be crucial for understanding the properties of melts in the deep mantle, and add a new dimension to the physics of terrestrial impact events.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2005
- Bibcode:
- 2005AGUFMMR12A..05M
- Keywords:
-
- 3914 Electrical properties;
- 3924 High-pressure behavior;
- 3944 Shock wave experiments;
- 8136 Impact phenomena (5420;
- 6022);
- 8147 Planetary interiors (5430;
- 5724;
- 6024)