Davide Sangiovanni, a research fellow at Linköping University, in the National Supercomputer Centre in Linköping. Image: Anna Nilsen.
Davide Sangiovanni, a research fellow at Linköping University, in the National Supercomputer Centre in Linköping. Image: Anna Nilsen.

A phenomenon that has previously only been seen when researchers simulate the properties of planet cores at extreme pressures has now also been observed in pure titanium at atmospheric pressure. This phenomenon involves chains of atoms dashing around at lightning speeds inside the solid material.

"The phenomenon we have discovered changes the way we think about mass transport in metals," says Davide Sangiovanni, researcher in the Division of Theoretical Physics at Linköping University in Sweden and principal author of a paper on this work in Physical Review Letters. "It explains properties of metals that we have, until now, not been able to understand. It's too early to say what this means in practical terms, but the more we know about how materials function in different conditions, the better possibilities we have to develop materials with new or improved properties."

In solid materials such as metals, the atoms are arranged in a well-organized crystal structure, at specific distances from each other. Diffusion in these crystalline materials typically occurs as isolated ‘rare’ hops of atoms into vacancies known as crystal defects.

In some materials, however, such as fast ion conductors at elevated temperatures or water (‘superionic ice’) and iron at the extreme pressures found in planetary-cores, long chains of atoms and ions can suddenly start to move at surprisingly high speed as a single entity. This process occurs on timescales of picoseconds or nanoseconds, and does not affect the crystal structure. The phenomenon is sometimes called ‘concerted diffusion’, ‘superionic diffusion’ or ‘liquid-like diffusion’, and has been described in a number of theoretical papers.

Together with colleagues at Linköping University and universities in Germany and Russia, Sangiovanni has now discovered that the same diffusion can take place in the cubic phase of pure titanium, at normal atmospheric pressures and at temperatures below titanium’s melting point.

Titanium, zirconium and hafnium, which are all in Group IVB of the periodic table, have several characteristic properties that researchers have not been able to explain – until now. "In the article, we show that the anomalous properties of Group IVB metals in their cubic structure originate from concerted diffusion, in which the atomic chains wriggle through the solid crystal," explains Sangiovanni.

This story is adapted from material from Linköping University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.