Researchers at the University of Tokyo used computer simulations to model the effects of elemental composition on the glass-forming ability of metallic mixtures. Image: Institute of Industrial Science, the University of Tokyo.Researchers from the Institute of Industrial Science at the University of Tokyo in Japan have used molecular dynamics calculations to simulate the glass-forming ability of metallic mixtures. They show that even small changes in composition can strongly influence the likelihood that a material will assume a crystalline versus a glassy state upon cooling. This work, reported in a paper in Science Advances, may lead to a universal theory of glass formation and cheaper, more resilient, electroconductive glasses.
Although a table might be set with expensive 'crystal' glasses, crystal and glass are actually two very different states that liquids, including liquid metals, can assume as they cool. A crystal has a defined three-dimensional lattice structure that repeats indefinitely, while glass is an amorphous solid that lacks long-range ordering.
Current theories of glass formation cannot accurately predict which metallic mixtures will 'vitrify' to form a glass and which will crystallize. A better, more comprehensive understanding of glass formation would be a great help when designing new recipes for mechanically tough, electrically conductive materials.
Now, researchers at the University of Tokyo have used computer simulations of three prototypical metallic systems to study the process of glass formation. "We found that the ability for a multi-component system to form a crystal, as opposed to a glass, can be disrupted by slight modifications to the composition," says first author Yuan-Chao Hu.
Stated simply, glass formation is the consequence of a material avoiding crystallization as it cools. This locks the atoms into a 'frozen' state before they can organize themselves into their energy-minimizing pattern. The researchers' simulations showed that a critical factor determining the rate of crystallization was the liquid-crystal interface energy.
The researchers also found that changes in elemental composition can lead to local atomic orderings that frustrate the process of crystallization, because these orderings are incompatible with the crystal's usual form. Specifically, these structures can prevent tiny crystals from acting as 'seeds' that nucleate the growth of ordered regions in the sample. In contrast with previous explanations, the scientists determined that the chemical potential difference between the liquid and crystal phases has only a small effect on glass formation.
"This work represents a significant advancement in our understanding of the fundamental physical mechanism of vitrification," says senior author Hajime Tanaka. "The results of this project may also help glass manufacturers design new multi-component systems that have certain desired properties, such as resilience, toughness and electroconductivity."
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.