Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Glass gives up secrets under pressure

14.12.2004


UNDER PRESSURE — The interior structure of germania was revealed when researchers squeezed a sample between these two piston anvils, shown with postdoctoral appointee Qiang Mei, up to 50,000 times atmospheric pressure.


PRESSURED TO CHANGE – The images above show how the structure of germanium-dioxide glass changes as it is subjected to increasing greater pressure. The structural units are about 1 nanometer, or one-billionth of a meter, across. The top image shows the material’s basic tetrahedral structure at normal pressures. In the second image, the tetrahedral structure begins to collapse when pressures reach about 50,000 times atmospheric pressure. In the bottom image, at 60,000 to 100,000 times atmospheric pressure, the structure becomes octahedral.


Glass is a mysterious material, but when researchers apply pressure, it reveals secrets.
Using a variety of techniques, researchers at Argonne National Laboratory saw for the first time ever, the atomic structure of a dense, purely octahedral glass that has eluded scientists for decades. They also witnessed a continuous structural change in the glass, disproving the theory that tetrahedral glasses go through a distinct transition between low- and high-density phases.

“Little is known about the structure of glass under pressure” said materials scientist Chris Benmore, “even though it is quite important. We put it in our cars and homes, and use it in many industrial applications, but how does the atomic structure react to extreme pressures?”


Benmore is a researcher in Argonne’s Intense Pulsed Neutron Source Division (IPNS). This division operates the IPNS, which provides neutrons for condensed matter physics, the study of atomic arrangements and motions in liquids and solids. IPNS is open to researchers from industry, academia and other national laboratories.

Glass is difficult to study because it is disordered and lacks a periodic crystal structure. Also, it needs to be studied under pressure, because, as Benmore said, “the glass structure pings right back when the pressure is lessened.” Researchers designed original pressure cell geometries for the research.

To witness the glass’ transition under pressure, Benmore and colleagues used a combination of tools:

  • Neutron diffraction studies at Argonne’s IPNS
  • X-ray diffraction at Argonne’s Advanced Photon Source, and
  • Molecular dynamic simulations.

Scientist Chris Tulk from Oak Ridge National Laboratory created novel pressure cells for both instruments in conjunction with other pressure-cell experts from the Carnegie Institution.

“Silica is the most important and most widely used glass,” said Benmore, “but we studied the softer germania (Ge) because it is a structural analog to silica and transforms to the octahedral form at much lower pressures than silica. Germania also provides a greater contrast in the neutron and the X-ray studies, so the details appear more clearly.”

At ambient pressure, Ge has an archetypal tetrahedral network glass structure. Four oxygen atoms enclose a germanium atom and share corners to create cages that are only a nanometer across.

Neutron revelations

The researchers began their experiments at the IPNS. Neutrons reveal structural and dynamic properties of materials, and they are sensitive to lighter elements such as oxygen.

Two piston anvils inside the IPNS’s Glass, Liquid, and Amorphous Materials Diffractometer squeezed a 100-cubic millimeter sample of germania dioxide (GeO2) to pressures up to five gigapascals, or 50,000 times atmospheric pressure.

IPNS revealed the mechanism of how GeO2’s tetrahedra collapse under pressure. Oxygen atoms were seen being squeezed into the sides of neighboring tetrahedra as the cages collapsed and the glass density increased.

In contrast to the IPNS, the APS reveals germanium atoms more clearly and can test smaller samples, which allows studies at higher-pressures. As a 1 cubic millimeter GeO2 sample was pushed from 60,000 to 100,000 times ambient pressure, researchers witnessed the tetrahedral cages collapsing and an average of five oxygen atoms organizing around the germanium atom before the octahedral glass was formed. This average coordination number of five still did not clearly resolve the question of whether this phase change in germania is continuous or discontinuous.

Researchers thought they may have seen a gradual mixture of five- and then six-fold germanium atoms in the structure as the pressure increased, but the result was still unclear. So they called on their colleagues at the National Research Council of Canada to perform molecular dynamic simulations in which a computer calculates molecular structure and behavior from first principles. “The simulations agreed with our data and revealed a germanate anomaly, that allows a distorted five-fold coordination of germanium to exist over a limited pressure range,” Benmore explained. “This provided evidence that germania glass transforms continuously, which disagrees with the popular two-state model.”

As researchers pressurized a GeO2 sample to 150,000 times ambient pressure, they witnessed a dense, disordered octahedral – eight-sided – structure inside glass for the first time. The angles of the internal structures were not the 90 and 180 degrees of a perfect octahedron; instead, the angles were near 90 and 165 degrees.

“We’ll continue to study this dense glass since it has never before been characterized,” said Benmore. “It is a challenge because of the pressures needed. Also, some glass scientists thought the glass would immediately crystallize if it became octahedral.”

This research, which has appeared in Physical Review of Letters, Vol. 93, No. 11, was highlighted in the Editors’ Choice in the October 1, 2004 issue of Science.

This is not the first time the team of Benmore and Tulk has shown that the two-state polyamorphic theories have been wrong. In 2003, Benmore, Tulk and colleagues discovered new metastable ice forms when studying ice under pressure. These new forms appear to contradict the widely held belief that the phase change in amorphous ice is discontinuous. — Evelyn Brown

Catherine Foster | EurekAlert!
Further information:
http://www.anl.gov

More articles from Physics and Astronomy:

nachricht Further Improvement of Qubit Lifetime for Quantum Computers
09.12.2016 | Forschungszentrum Jülich

nachricht Electron highway inside crystal
09.12.2016 | Julius-Maximilians-Universität Würzburg

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Electron highway inside crystal

Physicists of the University of Würzburg have made an astonishing discovery in a specific type of topological insulators. The effect is due to the structure of the materials used. The researchers have now published their work in the journal Science.

Topological insulators are currently the hot topic in physics according to the newspaper Neue Zürcher Zeitung. Only a few weeks ago, their importance was...

Im Focus: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

Researchers identify potentially druggable mutant p53 proteins that promote cancer growth

09.12.2016 | Life Sciences

Scientists produce a new roadmap for guiding development & conservation in the Amazon

09.12.2016 | Ecology, The Environment and Conservation

Satellites, airport visibility readings shed light on troops' exposure to air pollution

09.12.2016 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>