• Research Areas
• Glasses and Amorphous Oxides
  • Aluminosilicate Glass Structure
  • Borosilicate Glass Structure
  • Pressure effects on glass and melt structure
  • Insulating coatings for microelectronics
  • Amorphous metal oxides for optical coatings
• Order/Disorder in Minerals and Ceramic Materials
• Dynamics in Crystalline and Molten Silicates and Oxides

Aluminosilicate Glass Structure

We are currently working on several simple aluminosilicate glass ternary systems, to better refine the extent of disorder in the tetrahedral network structure, and the role of structural species that are not supposed to be present according to "conventional wisdom," but which are now suspected to be quite important in controlling some melt properties. The latter include aluminum cations with five instead of four oxygen neighbors, and non-bridging oxygens in "metaluminous" compositions, i.e. those along silica-feldspar binaries. NMR is essentially the only known way of quantifying these critical details in a glass. We have pioneered in the application of both high-field (14.1, 18.8 Tesla) MAS NMR to improve resolution of spectra of 27Al and other quadrupolar nuclides in glasses, and in the application of "triple quantum" (3QMAS) NMR to nuclides such as 27Al and 17O. The latter is especially useful in counting the fractions of non-bridging oxygens and of various network linkages such as Si-O-Si, Si-O-Al, and Al-O-Al, as shown below. An important focus of this work is to study the effects of temperature on the melt structure, by forming glasses at different cooling rates. Fast cooling samples the melt at a relatively high "fictive temperature" (Tf); slow cooling at a relatively low Tf. A thermodynamic analysis of the changes with T in speciation provides important data on enthalpies and heat capacities generated by such configurational changes.