Electronic, Structural, and Mechanical Properties of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>SiO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math> Glass at High Pressure Inferred from its Refractive Index
Sergey S. Lobanov, Sergio Speziale, Björn Winkler, Victor Milman, Keith Refson, Lukas Schifferle
Abstract
We report the first direct measurements of the refractive index of silica glass up to 145 GPa that allowed quantifying its density, bulk modulus, Lorenz-Lorentz polarizability, and band gap. These properties show two major anomalies at $\ensuremath{\sim}10$ and $\ensuremath{\sim}40\text{ }\text{ }\mathrm{GPa}$. The anomaly at $\ensuremath{\sim}10\text{ }\text{ }\mathrm{GPa}$ signals the onset of the increase in Si coordination, and the anomaly at $\ensuremath{\sim}40\text{ }\text{ }\mathrm{GPa}$ corresponds to a nearly complete vanishing of fourfold Si. More generally, we show that the compressibility and density of noncrystalline solids can be accurately measured in simple optical experiments up to at least 110 GPa.