Almost 150 years after its discovery and subsequent addition to Mendeleev’s periodic table, gallium continues to reveal its secrets. Scientists from the University of Auckland have recently discovered new aspects of the metal’s structure and behaviour.

First discovered in 1875 by French chemist Paul-Emile Lecoq de Boisbaudran, gallium is known for its low melting point—so low that a spoon made of gallium would melt in a cup of tea. This unusual metal is also a key ingredient in semiconductor manufacturing.

One surprising discovery concerns the behavior of gallium at the atomic level.

Unlike most metals, gallium exists as “dimers” (pairs of atoms) and is less dense as a solid than as a liquid, similar to how ice floats on water. Gallium has “covalent bonds”, where atoms share electrons, which is unusual for a metal.

The new study shows that although these bonds disappear at the melting point, they reappear at higher temperatures.

This contradicts long-held assumptions and requires a new explanation for gallium’s low melting point. The researchers suggest that the key to this may be the large increase in entropy (a measure of disorder) that occurs when bonds break free, freeing up atoms.

A breakthrough in understanding gallium

“In three decades of literature on the structure of liquid gallium, there was a fundamental assumption that was clearly not true,” says Professor Nicola Gaston from the University of Auckland and Waipapa Taumata Rau from the MacDiarmid Institute for Advanced Materials and Nanotechnology.

The research was carried out by Dr. Steph Lambie, currently a postdoctoral researcher at the Max Planck Institute for Solid State Research in Germany, and Dr. Christa Steenbergen of the Victoria University of Wellington and the MacDiarmid Institute.

The breakthrough came when Lambie, then a graduate student at the university and the MacDiarmid Institute, meticulously pored over the previous decades of scientific literature and compared temperature data to build the full picture.

Their findings were recently published in a scientific journal Material Horizons .

Gallium applications and historical significance

Understanding the precise processes in gallium, and particularly how it changes with temperature, is crucial to advances in nanotechnology, in which scientists manipulate matter to create new materials. The metal is used to dissolve other metals and helps create liquid metal catalysts and “self-assembled structures,” where disordered materials spontaneously structure.

The zinc “snowflakes” were created by crystallizing zinc in liquid gallium in a previous project involving Gaston, Lambie and Steenbergen.

Gallium was predicted even before it was discovered. When Russian chemist Dmitri Mendeleev created the first periodic table in 1871, arranging the elements in order of increasing atomic number, he left gaps for missing elements suggested by known elements.

Gallium, which is obtained from minerals and rocks such as bauxite, does not occur naturally in its pure form. The metal is also used in semiconductors, light-emitting diodes and laser diodes, solar panels, high-performance computers, aerospace and defense, and as an alternative to mercury in thermometers.

Intriguingly, scientists searching for traces of past life on Mars think gallium offers clues as a chemical “fingerprint” that preserves traces of past microbial life, according to researchers from the university’s School of the Environment and Te Ao Marama Fundamental Research Centre.