Resolving a Six-Decade-Long Controversy: Flaws Traverse Diamond Quicker Than Sonic Velocity

An illustration depicts a powerful laser strike coming from the top right corner and interacting with a diamond crystal. This interaction initiates elastic and plastic waves (depicted as curved lines) throughout the substance. The laser impact gives rise to linear anomalies, termed dislocations, at the points of contact. These dislocations advance through the diamond at velocities surpassing the transverse sonic speed, leaving in their wake stacking faults—the lines that radiate outward from the point of impact. Credit: Greg Stewart/SLAC National Accelerator Laboratory

The Dual Nature of Material Defects

The velocity at which defects move through materials can either reinforce the material or lead to catastrophic failure. Understanding this speed has implications for areas such as seismic activity, structural integrity, and high-precision manufacturing.

A Milestone in Materials Science

After 50 years of contentious discussions, investigators have revealed that minute linear imperfections, or dislocations, can traverse through a material at a speed that exceeds that of sound waves.

Dislocations contribute to the robustness and malleability of metals but can also be the reason behind catastrophic material failure—as demonstrated when a soda can’s pull tab is activated.

Their rapid movement grants scientists a fresh perspective on the diverse kinds of damage these defects could inflict on various materials under extreme conditions—from rocks being torn asunder during seismic events to aircraft protective materials distorted by extreme stress, according to Leora Dresselhaus-Marais, a faculty member at both the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University, who spearheaded the study alongside Professor Norimasa Ozaki from Osaka University.

Methodology and Findings

Until recently, direct measurements of how rapidly dislocations spread had not been possible. Dresselhaus-Marais and her team employed X-ray radiography techniques, akin to those used in medical imaging, to measure dislocation speed in diamonds, yielding insights that could be generalized to other materials. The study was published on October 5 in the scientific journal, Science.

Debating Sonic Speed

For nearly six decades, the scientific community had been divided on whether dislocations could move through materials faster than sound. Some studies had negated this possibility, but computational models suggested otherwise, under certain conditions.

The difficulties lie in the two types of sound waves in solids—longitudinal and transverse waves—and the fact that sound moves much faster in solid substances compared to air or water. Knowledge about dislocations surpassing these sonic barriers has significant scientific and practical implications, particularly in understanding unexpected failures.

Kento Katagiri, a postdoctoral scholar in the research group and the paper’s first author, emphasized the need for further investigation into this kind of rapid material failure.

Groundbreaking Observations

To capture the first direct images of dislocation speeds, researchers employed an X-ray free-electron laser at the SACLA facility in Japan on synthetic diamond crystals. Diamonds provide an ideal setting for these high-speed X-ray imaging experiments due to their simpler deformation mechanisms compared to metals.

When dislocations intersect, they either attract or repel each other, creating new dislocations. In a can of soda, the lid contains numerous existing dislocations which multiply exponentially when opened, leading to complete failure as the can’s top flexes and the pop top detaches.

According to Dresselhaus-Marais, diamond might be considerably harder than metal, but when subjected to sufficient shock, it forms billions of dislocations.

Future Directions

Katagiri revealed that future studies will aim to determine if dislocations can exceed the higher, longitudinal sonic speed in diamond, necessitating even more powerful laser shocks. Achieving this will qualify them as truly supersonic.

Citation

Reference: “Transonic dislocation propagation in diamond” by Kento Katagiri et al., 5 October 2023, Science. DOI: 10.1126/science.adh5563

Leora Dresselhaus-Marais is associated with the Stanford Institute for Materials and Sciences (SIMES) at SLAC as well as the Stanford PULSE Institute. Collaborating institutions include Osaka University, Japan Synchrotron Radiation Research Institute, RIKEN SPring-8 Center, and Nagoya University in Japan; DOE’s Lawrence Livermore National Laboratory; Culham Science Center in the UK; and École Polytechnique in France. The project received substantial funding from the U.S. Air Force Office of Scientific Research.

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More about Dislocation Propagation in Diamond Faster Than Speed of Sound

• SLAC National Accelerator Laboratory
• Osaka University
• SACLA X-ray free-electron laser
• Journal Science
• U.S. Air Force Office of Scientific Research
• DOI for the Paper
• Transverse and Longitudinal Waves
• Material Science and Engineering
• Understanding Earthquake Ruptures
• X-ray Radiography Techniques