Using sophisticated molecular dynamics computer simulations, the scientists found a common vibrational mechanism underlying the properties of amorphous materials like glass. Image: Institute of Industrial Science, The University of Tokyo.Scientists from the Institute of Industrial Science at the University of Tokyo in Japan have used molecular dynamics simulations to better understand the unusual properties of amorphous materials such as glass. They found that certain dynamical defects help explain the allowed vibrational modes inside glassy materials. The scientists report their findings, which may help to control the properties of amorphous materials, in a paper in Nature Physics.
Sometimes expensive glass is advertised as ‘crystal’, but to material scientists this could not be further from the truth. Crystals are made up of atoms arranged in orderly, repeating patterns, while glass is a disordered, amorphous solid.
At low temperatures, many disordered materials have properties that are very similar to each other, including specific heat and thermal conductivity. Additionally, these properties differ significantly from those of materials made from ordered crystals. Furthermore, at a certain frequency range, glassy materials have a larger number of available vibration modes than crystals, known in the field as the ‘boson peak’. While various theories have been proposed, the underlying physical mechanisms for these observations have remained a question of active research.
Now, scientists from the University of Tokyo have used sophisticated molecular dynamics computer simulations to numerically calculate the transverse and longitudinal dynamic structure factors of model glasses over a wide range of frequencies. They found that string-like vibrational motions, in which curved lines of particles packed into a ‘C’ shape inside the material move together, could be important drivers of the anomalous effects.
“These dynamical defects provide a common explanation for the origin of the most fundamental dynamic modes of glassy systems,” says first author Yuan-Chao Hu. In addition to the boson peak, these string-like dynamic defects may be responsible for the types of fast and slow relaxation observed in the particles making up glass.
This research has many important implications for both science and industry because the boson peak is found in many systems, not just glasses. “We show that the boson peak originates from quasi-localized vibrations of string-like dynamical defects,” says senior author Hajime Tanaka. Being able to explain this feature will shed light on many other types of disordered materials. It will also benefit the many users of smart devices, because almost all smartphones, tablets and touchscreen laptops utilize glass materials.
This story is adapted from material from the University of Tokyo, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.