Synopsis: Atomic avalanches show up in x rays

State-of-the-art x-ray scattering demonstrates sudden avalanche-like structural changes in cobalt.
Synopsis figure
Credit: C. Sanborn et al., Phys. Rev. Lett. (2011)

Certain crystals switch their structural pattern by tiny but coordinated movements of the constituent atoms. Recent experiments have suggested that these transitions are not wholesale conversions, but a series of sudden, localized shifts inside the crystal. These so-called avalanches have now been observed using x rays by Christopher Sanborn at Boston University, US, and colleagues there and at McGill University, Canada. The results, published in Physical Review Letters, show that atomic behavior in crystals shares similarities with earthquakes.

A martensitic transition is a solid-solid phase transition in which the crystal reconfiguration is usually accompanied by strain. First observed in a type of hard steel called martensite, it was later detected in other materials, such as shape-memory alloys. Observations during martensitic transitions have detected spikes in acoustic emissions and heat flow that imply avalanching, but seeing these structural changes directly required developing a technique that could spatially resolve them from avalanches as they happened.

This was achieved with coherent x-ray beams that are now produced at synchrotron facilities. Using the Advanced Photon Source in Argonne National Laboratory, the authors studied a martensitic transition in cobalt at a temperature of about 447 °C. Coherent x rays scattering off the cobalt interfere with each other to produce a speckle pattern on a CCD camera. Any sudden change in a group of speckles corresponds to an avalanche. The team measured avalanche sizes between 100 nanometers and 10 microns. The rate and distribution of avalanches during strain-relieving structural rearrangements for the phase transition resemble the statistics for aftershocks following an earthquake. – Michael Schirber


Features

More Features »

Announcements

More Announcements »

Subject Areas

Materials Science

Previous Synopsis

Particles and Fields

Perhaps no “bump” in the data

Read More »

Next Synopsis

Interdisciplinary Physics

The importance of being noisy

Read More »

Related Articles

Synopsis: Flexible Electronics, Heal Thyself
Electronics

Synopsis: Flexible Electronics, Heal Thyself

A suspension of copper particles fixes breaks in electronic connections, providing a possible way to heal damaged circuits. Read More »

Viewpoint: Crystalline Metals Effortlessly Fit the Mold
Condensed Matter Physics

Viewpoint: Crystalline Metals Effortlessly Fit the Mold

Molding crystalline metals like silver into nanopillar structures is both possible and easier to achieve for narrower pillars, in contrast with other materials. Read More »

Viewpoint: Pushing Towards Room-Temperature Superconductivity
Condensed Matter Physics

Viewpoint: Pushing Towards Room-Temperature Superconductivity

Two independent studies report superconductivity at record high temperatures in hydrogen-rich materials under extreme pressure. Read More »

More Articles