Structure of germanate glasses

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Structure of germanate glasses J.F. Stebbins,
Stanford University, DMR 0404972
Glasses containing germanium oxide (GeO2) are
widely used in optical components such as
fiber-optic waveguides. Alkali germanate glasses
have been studied for decades as a simple
system whose physical properties such as density
and refractive index change with composition in a
very complex way. The nature of the underlying
structural changes have remained controversial,
though. This group has recently used
high-resolution, triple quantum magic-angle
spinning (3QMAS) nuclear magnetic resonance
(NMR) to, for the first time, directly observe
and quantify the different types of oxide ion
sites in sodium germanate glasses. These results
clearly show that unlike the well-known case of
silicate glasses, the addition of Na2O to GeO2
does not initially produce non-bridging oxygens,
but instead that the coordination number of Ge
increases as sites with five and/or six neighbors
are formed from those with four neighbors. These
findings will be very helpful in the
long-standing goal of linking atomic-scale
structure to technologically important glass
properties.
High-resolution (3QMAS) NMR spectrum for
oxygen-17 in a germanate glass with about 19
Na2O. A small peak for non-bridging oxygens can
clearly be seen, but is much smaller than would
be seen for a corresponding silicate. Peaks for
oxygens with two 4-coordinated Ge neighbors, and
one 4- plus one 5- or 6-coordinated neighbor, are
well-resolved and are assigned based on our
detailed studies of crystalline model compounds.
(J. Phys. Chem. B 110, 12427 2006)
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Structure and properties of oxide glasses
career development for the high-tech materials
industry J.F. Stebbins, Stanford University, DMR
0404972
This program trains students with diverse
backgrounds in the science of oxide glass
structure and properties. Three recent examples
include T.J. Kincenski, who finished his Ph.D. in
Spring of 2005 and has gone on to a career in the
research lab of Corning, Inc. Lin-Shu Du, who
was supported in this program as a postdoc and
who left in early 2006 for a research position at
a chemical company developing amorphous materials
for the electronics industry (as well as many
other products) and Jingshi Wu, a talented young
woman with a mineralogy background who is
interested in high-tech oxide materials and who
recently joined our Ph.D. program.