• Research Areas
• Glasses and Amorphous Oxides
• Order/Disorder in Minerals and Ceramic Materials
  • Order/disorder in high-pressure silicate minerals
  • Cation disorder and vacancies in ionicly conducting ceramics
  • Cation order/disorder and substitution mechanisms in oxides with magnetic cations
• Dynamics in Crystalline and Molten Silicates and Oxides

Cation order/disorder and substitution mechanisms in oxides with magnetic cations

Most solid-state NMR studies on minerals and other silicates and oxides have been done on materials with very low contents of ions with unpaired electron spins (e.g. most transition metals and rare earth elements), because the magnetic effects of such cations can produce severe broadening of spectra and loss of resolution. We recently found that in at least some cases, minerals with moderate (a few wt%) contents of magnetic oxide components such as FeO may instead show small, well-resolved, extra peaks in 27Al and 29Si NMR spectra that are moved well outside of normal ranges of chemical shifts by either "contact" or "pseudocontact" effects. These resonances as marked as well by large and easily measurable changes in frequency with temperature. The positions and intensities of such peaks potentially carry interesting new types of information about short-range order/disorder in minerals involving geochemically important elements such as Fe and REE. We are currently working to understand these effects and to try to use them to constrain mechanisms of solid solutions, in high pressure silicates and in phosphate-silicate solid solutions such as zircon, monazite, and xenotime.