T184 Frontiers in High-Pressure Research: In Honor of Wendy Li-Wen Mao, 2013 MSA Awardee

Monday, 28 October 2013
1:00 PM - 5:00 PM
Room 207

DETERMINATION OF EQUATION OF STATE OF AMORPHOUS MATERIALS AT HIGH PRESSURE USING NANOSCALE TRANSMISSION X-RAY MICROSCOPY

Paper number: T184-9
Program: Technical Sessions
Time: 3:00 PM – 3:15 PM

Authors

  • Yu Lin Presenting Author
    Stanford University, Stanford, CA
  • Wendy Mao
    Stanford University, Stanford, CA

Abstract

The effect of pressure (P) on volume (V) has long been recognized as a fundamental thermodynamic relationship. Experimental determination of accurate P-V relationships is currently limited to well-crystallized solids where x-ray or neutron diffraction can yield accurate unit cell data at high pressures. However, for amorphous and poorly crystalline materials, we still lack this fundamental equation of state data. Development of synchrotron transmission x-ray microscopy (TXM) with 30 nm spatial resolution has enabled volume determination by imaging with accuracy rivaling x-ray diffraction of crystalline solids.

Group IV elements, including carbon, silicon, and germanium, both alone and in combination, exhibit a variety of amorphous forms that show unique behavior upon compression. Compressing glassy carbon above 40 GPa, we observed a new carbon allotrope with a fully sp3-bonded amorphous structure and diamond-like strength. Amorphous SiO2 and GeO2 are classic network-forming glasses which display rich structural polymorphism at high pressure. We used TXM for accurate P-V determination of glassy carbon, SiO2 glass, and GeO2 glass in a cross diamond anvil cell. The results provide guidance for understanding the mechanisms of the structure and bonding changes in these amorphous materials at high pressure.