18 July 2016

"Free" oxide ions detected in silicate glasses

Atomic model of glass showing non-bridging and bridging oxygens, and ‘free’ oxide ions. Atomic model of glass showing non-bridging and bridging oxygens, and ‘free’ oxide ions.

Using an advanced technique, scientists discover that one of the most common substances in our everyday lives — glass — is more complex than we thought.

First, some background

Made up largely of silicon and oxygen, glass plays a huge role in our lives as the building block of products from windowpanes to fiber-optic cables and other technological materials. So it's important to understand, predict and optimize the molecular structure of different types of glass. It's particularly important to understand the role of oxygen ions, which in conventional models of most glass-forming compositions always bond to one or two silicon atoms.

What is the finding?

Scientists in the MagLab's Nuclear Magnetic Resonance (NMR) Facility used a challenging double-resonance NMR technique to probe the structure of a specific kind of glass made up of CaO, MgO and SiO2. For the first time, they have directly detected so-called "free" oxide ions in the compound's structure — ions that are not bound to silicon. Their finding contradicts standard models of glass structure.


This research was conducted in the MagLab 800 MHz solid state NMR system at the MagLab's NMR Facility.

Why is this important?

These findings indicate that standard models need to be revised to include a more complex and disordered network structure than previously predicted. This may have major impacts on thermodynamic models of melt and glass properties, as well as on phase diagrams for technologically important glasses.

In addition, this experiment shows that this promising technique (known as CP-HETCOR) can be used for making observations on different glass compositions in the future. The technique was able to measure the transfer of a property called nuclear spin polarization between the oxygen and silicon atoms.

Who did the research?

Ivan Hung1, Zhehong Gan1, Peter L. Gor'kov1, Derrick C. Kaseman2, Sabyasachi Sen2, Michelle LaComb3, Jonathan F. Stebbins3

1NHMFL; 2University of California, Davis; 3Stanford University

Why did this research need the MagLab?

This double-resonance NMR experiment is very challenging due to the low natural abundances, low sensitivities and small couplings between the oxygen and silicon nuclei. The National MagLab offers the high magnetic fields, sensitive NMR instruments and innovative pulse sequences that make observation of free oxide ions possible.

Details for scientists


This research was funded by the following grant: G.S. Boebinger (NSF DMR-1157490); J.F. Stebbins (NSF EAR-1521055); S. Sen (NSF DMR-1505185)

For more information, contact Zhehong Gan.


  • Research Area: Biology,Geochemistry, Magnet Resonance Technique Development
  • Research Initiatives: Materials
  • Facility / Program: NMR/MRI
  • Year: 2016
Last modified on 18 July 2016