Metallic glass is a significantly advanced alloy with potential for numerous engineering uses. In many ways, it resembles a solid form due to its exquisite metal appearance, extreme flexibility, tremendous strength, and tightly packed atomic structure.
This unwavering conviction has now been refuted. The existence of liquid-like atoms in metallic glasses has recently been demonstrated by Prof. Haiyang Bai of the Institute of Physics of the Chinese Academy of Sciences (CASE). These atoms exhibit the behaviors of high-temperature liquid atoms, demonstrating the bimodal nature of metallic glasses.
The findings were released in Nature Materials.
Generally speaking, there are two states of condensed matter: solid and liquid. Matter can exist in unique states that concurrently display some features of both solids and liquids under extreme situations or in particular systems. In this case, liquid-like, rapidly diffusing atoms that can move quickly even at low temperatures could be present in solids.
For instance, under high pressure and high temperatures, ice adopts a “superionic” condition. In this condition, O atoms are locked in their sublattices, but H atoms can flow freely. In addition to the sophisticated batteries’ Li-conducting materials, which are gaining increasing attention in research and engineering, these unusual states have also been seen in the Earth’s inner core.
The results of this study showed that metallic glasses with tightly packed atoms do indeed contain liquid-like atoms. They discovered that when a liquid’s viscosity deviates from Arrhenius behavior, not all atoms participate in cooperative flow and eventual solidification.
This was the result of combining extensive dynamical experiments with computer simulations. In fact, some atoms exhibit persistent liquid-like atoms that cause quick relaxation at relatively low temperatures because they can preserve liquid Arrhenius behavior even when the system is cooled to a glass state.
A glassy solid is essentially mostly solid and a small part liquid. Even at room temperature, liquid-like atoms in a glassy solid can diffuse just as easily as in its liquid state, with an experimentally determined viscosity as low as 107 Pa s, while the viscosity of the solid part is larger than 1013 Not.
Haiyang Bai, Professor, Institute of Physics of the Chinese Academy of Sciences
These results offer a more precise microscopic view of glasses. The relationship between the dynamics of glass materials and their properties can now be better understood by scientists, thanks to this new image. For instance, liquid-like atoms can influence the ductility and anelasticity of glasses.
Moreover, the close connection between liquid-like atoms and disordered structure has implications for research into the topological causes of fast diffusion in solids such as superionic-state materials and ion conductors.
The Natural Science Foundation of Guangdong Province, the Strategic Priority Research Program of CAS, the National Science Foundation of China, and others provided funding for this study.
Chang, C. et al. (2022) Liquid-like atoms in dense-packed solid glasses. NatureMaterials. doi:10.1038/s41563-022-01327-w.