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ADVANCED MATERIALS & PROCESSES • OCTOBER 2014 11
to another as it is placed under high pressure.
The new findings may have implications for
understanding how glasses and similar amor-
phous materials respond at the atomic scale
under stress, says materials science professor
Sabyasachi Sen. Boron oxide is often added to
glass to control a range of properties, including
chemical durability, flow resistance, optical
transparency, and thermal expansion. It is
known that the structure around the boron
atoms in borosilicate glass changes with pres-
sure and temperature, switching from a flat tri-
angular configuration with three oxygen atoms
surrounding one boron atom to a four-sided
tetrahedron, with four oxygen atoms surround-
ing one boron.
Previously, researchers could only study
these structures in one state or the other, but
not in transition. Sen and graduate student
Trenton Edwards developed a probe that en-
ables them to make nuclear magnetic reso-
nance measurements of the environment of
boron atoms in glass under pres-
sures up to 2.5 GPa. They found
that under pressure, the flat trian-
gles of boron and three oxygen
atoms first deform into a pyramid
shape, with the boron atom
pushed up. That may bring it close
to another oxygen atom, and let
the structure turn into a tetrahe-
dron, with four oxygen atoms sur-
rounding one boron.
Although glass is structurally
isotropic and the stress on the
glass is the same in all directions,
the boron atoms respond by mov-
ing in one direction in relation to
the rest of the structure. “This is
an unexpected finding that may
have far-reaching implications for
understanding a wide range of stress-induced
phenomena in amorphous materials,” notes
Sen. .
A super-advanced system for high-resolution
imaging and spectroscopy, the first of its kind
in the UK, will be installed at the University of
Bristol thanks to a grant from the Engineer-
ing and Physical Sciences Research Coun-
cil. The NanoESCA is an ultra-high vacuum
photo electron emission microscopy system
with state-of-the-art resolution for real-space
and momentum-space imaging and spec-
troscopy. The new instrument will enable the
electronic properties and chemical composition
of thin layers of materials to be revealed and
quantified by a nondestructive technique. The
NanoESCA facility will be installed in the Uni-
versity of Bristol’s Centre for Nanoscience and
Quantum Information in a dedicated ultra-quiet
laboratory in 2015. .
NanoESCA. Courtesy of University of Bristol.