Gallium, a metal that melts in the hand, has just surprised scientists.
At the atomic level, gallium exhibits peculiarities. In its solid state, its atoms form pairs with covalent bonds, typical of non-metals. Upon melting, these bonds were thought to persist, explaining some properties. However, detailed simulations indicate they disappear at the melting point, only to reappear later with an increase in temperature.
The heat of the hand is enough to liquefy gallium.
Image Wikimedia
This evolution of the bonds helps explain a long-observed but poorly understood phenomenon: the electrical resistivity of liquid gallium initially decreases after melting, then increases non-linearly with heat.
Another discovery concerns the surface of liquid gallium. Contrary to the idea of total disorder, it exhibits subtle geometric patterns across approximately three atomic layers. Furthermore, oxidation reinforces this order, while impurities like bismuth disrupt it, revealing a hidden structure that only fades over a distance of about 0.85 nanometers.
These results were obtained through large-scale simulations and machine learning, combining older experimental data. The study, published in
Materials Horizons, resolves contradictions in the scientific literature and allows for better modeling of atomic behavior.
Understanding these mechanisms is valuable for emerging technologies. Gallium, used in semiconductors and solar panels, could see its applications expand into flexible electronics, batteries, and catalysts, thanks to a better grasp of its electrical and thermal properties.
Covalent bonds in metals
Covalent bonds are links between atoms where electrons are shared, which is common in non-metals like carbon. Metals, on the other hand, have free electrons that allow for good electrical conduction. Gallium is unusual because, in its solid state, it forms atomic pairs with covalent bonds, more closely resembling a non-metal.
This characteristic influences its properties, such as its lower density in the solid state than in the liquid state, similar to ice floating on water.
Understanding these bonds is useful because they affect how materials conduct electricity and heat. In the case of gallium, the transformation of bonds with temperature explains why its resistivity changes, offering leads for designing alloys with adjustable properties.