Nearly 150 years after gallium was first discovered and added to the periodic table, scientists at the University of Auckland have uncovered previously unknown details about the metal’s atomic structure and behavior.
Gallium was discovered in 1875 by French chemist Paul Émile Lecoq de Boisbaudran. It is best known for its unusually low melting point, which allows a gallium spoon to melt in a cup of hot tea. The metal also plays an essential role in semiconductors and many modern electronic technologies.
The newly reported findings focus on how gallium behaves at the atomic level, revealing properties that challenge decades of scientific understanding.
A Strange Metal With Even Stranger Atomic Behavior
Gallium already stands out from most metals in several ways. Its atoms naturally pair up into `dimers,’ meaning they exist as bonded pairs. It is also one of the few substances that is less dense as a solid than as a liquid, much like ice floating on water.
Another unusual feature is that gallium forms `covalent bonds,’ in which atoms share electrons. This type of bonding is far more common in nonmetals than in metals.
Scientists had long believed those covalent bonds disappeared when gallium melted. However, the new study found that although the bonds vanish at the melting point, they unexpectedly return when the liquid is heated to even higher temperatures.
This discovery overturns a long accepted assumption and suggests a new explanation for gallium’s remarkably low melting point. The researchers propose that when the bonds break apart, the resulting increase in entropy, a measure of disorder, frees the atoms and makes melting easier.
“Thirty years of literature on the structure of liquid gallium has had a fundamental assumption that is evidently not true,” says Professor Nicola Gaston, of Waipapa Taumata Rau, University of Auckland and the MacDiarmid Institute for Advanced Materials and Nanotechnology.
Revisiting Decades of Research
The study was conducted by Dr. Steph Lambie, now a postdoctoral researcher at the Max Planck Institute for Solid State Research in Germany, Professor Nicola Gaston, and Dr. Krista Steenbergen of Victoria University of Wellington and the MacDiarmid Institute.
The breakthrough came while Lambie was completing a PhD at the University of Auckland and the MacDiarmid Institute. By carefully reviewing decades of published research and comparing measurements collected at different temperatures, Lambie assembled a more complete picture of gallium’s behavior.
The findings were published in Materials Horizons in a paper titled “Resolving Decades of Debate: The Surprising Role of High-Temperature Covalency in the Structure of Liquid Gallium.”
Why Understanding Gallium Matters
A better understanding of how gallium changes with temperature could benefit nanotechnology, where researchers manipulate matter at extremely small scales to create new materials with specialized properties.
Gallium is also valuable because it can dissolve other metals, making it useful for producing liquid metal catalysts and `self-assembling structures,’ in which disordered materials spontaneously organize themselves into ordered forms.
In an earlier project, Gaston, Lambie, and Steenbergen used liquid gallium to crystallize zinc into intricate `snowflake’ structures.
From Predicted Element to Modern Technology
Gallium was predicted before it was ever discovered. In 1871, Russian chemist Dmitri Mendeleev created the first periodic table by arranging elements according to increasing atomic numbers and intentionally left empty spaces for elements he believed had yet to be found. Gallium later filled one of those predicted gaps.
The metal is extracted from minerals and rocks such as bauxite and does not occur naturally in its pure form. Today, gallium is widely used in semiconductors, telecommunications equipment, LEDs, laser diodes, solar panels, high performance computing, the aerospace and defense industries, and as a safer alternative to mercury in thermometers.
Researchers are also investigating whether gallium could help identify signs of ancient life on Mars. Scientists at the University’s School of Environment and Te Ao Mārama — Centre for Fundamental Inquiry are studying whether the metal can preserve traces of past microbial life as a chemical `fingerprint.’
The name gallium comes from Gaul, the ancient Latin name for France, honoring the nationality of its discoverer.