Glass - Back to the Future!

Presenting Author:
Adrian Wright

article posted 19 May 2016

Professor Adrian C. Wright
Before his retirement Adrian Wright was Professor of Amorphous Solid-State Physics at the University of Reading. He received his B.Sc (Chemistry), Ph.D. (Physical Chemistry) and D.Sc. degrees from the University of Bristol. Since moving to Reading, initially as an ICI Postdoctoral Fellow, he has spent periods of sabbatical leave at the Xerox Palo Alto Research Center, the Stanford Synchrotron Radiation Laboratory, Argonne National Laboratory, the University of California Los Angeles, the University of Florida Gainesville and the New York State College of Ceramics. His research interests comprise neutron scattering and modelling studies of the structure and dynamics of a wide range of inorganic glasses and other amorphous solids. He was President of the Society of Glass Technology from 2002 to 2004, and has served on both the Steering Committee and Council of the International Commission on Glass.

Density Fluctuations in Single-Component Glasses

Adrian C. Wright1*, Natalia M. Vedishcheva2
1J.J. Thomson Physical Laboratory, University of Reading, Whiteknights, Reading, RG6 6AF, U.K.
2Institute of Silicate Chemistry of the Russian Academy of Sciences, Nab. Makarova 2, St. Petersburg, 199034, Russia.

The random network and cybotactic theories of the structure of single-component glasses, such as SiO2, differ in respect of the frequency of occurrence and size of crystalline-like (cybotactic) groupings within the vitreous network, and hence of the expected form of the spatial fluctuations in their average number density, ρ°. The RMS fluctuations in average number density, <Δρ²>, in vitreous SiO2, GeO2 and B2O3, calculated from the zero-Q limit of the static structure factor, S(Q), are compared to those predicted by these theories. Assuming a purely random network, exhibiting density fluctuations with a Gaussian distribution, it is shown that the probability of finding regions (cybotactic groupings) with the density of the crystalline polymorph formed upon devitrification is much higher for vitreous SiO2 than for GeO2. The case of B2O3 is much more complicated in that, for the (metastable) super-cooled liquid and the glass just below the glass transition temperature, Tg, there is extra small-Q scattering arising from regions of inhomogeneity ~15 Ä in size. These regions of inhomogeneity disappear for vitreous B2O3 equilibriated at temperatures below 240°C, and it is concluded that they are associated with the rapid variation in the equilibrium boroxol group fraction through the glass transition region.