Gallium bonds found to return in hot liquid metal
University of Auckland researchers say gallium’s unusual covalent bonds reappear at high temperatures, changing a long-held view of the metal.
By Priya Raghavan · Science Reporter
3 min read
Researchers at the University of Auckland say they have identified a hidden behavior in gallium that changes how scientists explain the metal’s low melting point. The finding matters because gallium is used in electronics and materials research, and its odd atomic structure affects how it performs in those technologies.
The work, reported in the journal Materials Horizons, examined how gallium atoms bond as the metal is heated. According to the university, scientists had generally assumed that gallium’s covalent bonds disappear when it melts and stay gone in the liquid state.
The study found a different pattern. The researchers report that the bonds break at the melting point, then form again when liquid gallium reaches higher temperatures.
A metal with unusual bonds
Gallium has stood apart since its discovery in 1875 by French chemist Paul Émile Lecoq de Boisbaudran, the University of Auckland said. It melts just above room temperature, which is why a gallium spoon can liquefy in hot tea.
The metal also behaves unlike most metals at the atomic level. According to the university, gallium atoms form bonded pairs known as dimers, and solid gallium is less dense than its liquid form, a property often compared with ice floating on water.
Another unusual feature is gallium’s covalent bonding, in which atoms share electrons. The University of Auckland said that kind of bonding is more often associated with nonmetals, making gallium a difficult case for standard explanations of metallic structure.
The new work offers a revised explanation for why gallium melts so easily. The researchers propose that when the bonds break, the increase in entropy, or atomic disorder, gives the atoms more freedom and helps the solid turn to liquid.
“Thirty years of literature on the structure of liquid gallium has had a fundamental assumption that is evidently not true,” said Professor Nicola Gaston of Waipapa Taumata Rau, University of Auckland and the MacDiarmid Institute for Advanced Materials and Nanotechnology.
Rechecking decades of measurements
The study was conducted by Dr. Steph Lambie, Gaston and Dr. Krista Steenbergen of Victoria University of Wellington and the MacDiarmid Institute, according to the University of Auckland. Lambie did the work while completing a PhD at the University of Auckland and the MacDiarmid Institute, and is now a postdoctoral researcher at the Max Planck Institute for Solid State Research in Germany.
The university said the result came from a careful review of earlier research and a comparison of measurements taken at different temperatures. The paper is titled “Resolving decades of debate: the surprising role of high-temperature covalency in the structure of liquid gallium.”
According to the university, a clearer account of gallium’s temperature-dependent structure could aid nanotechnology, liquid metal engineering and semiconductor research. Gallium can dissolve other metals, which makes it useful in liquid metal catalysts and in self-assembling structures, where disordered materials organize into ordered forms.
In earlier work, Gaston, Lambie and Steenbergen used liquid gallium to crystallize zinc into snowflake-like structures, the university said. Researchers at the University of Auckland’s School of Environment and Te Ao Mārama — Centre for Fundamental Inquiry are also studying whether gallium can preserve chemical traces of ancient microbial life on Mars.
Gallium was anticipated before its discovery. The University of Auckland said Dmitri Mendeleev left spaces in his early periodic table for elements that had not yet been found, and gallium later filled one of those gaps.
The university said gallium is extracted from minerals and rocks including bauxite and does not occur naturally in pure form. It is used in semiconductors, telecommunications equipment, LEDs, laser diodes, solar panels, high-performance computing, aerospace and defense systems, and some thermometers as an alternative to mercury.
This story draws on original reporting from ScienceDaily.