Beyond the “Sound Barrier” to Get the Heat Out

Neutron scattering reveals supersonic particles that carry heat and may improve electronics and sensors.


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    Credit: Oak Ridge National Laboratory

    Heat usually moves by atomic vibrations that are limited by the speed of sound. Heat also can move by particles (phasons) related to atomic rearrangements that change with the movement of waves in the crystal structure. Using neutron scattering, scientists discovered supersonic phasons that could remove harmful heat in electronics and send signals faster. Phasons were observed in a mineral containing titanium (gray) and silicate (orange) polyhedrons linked at their corners. (Oxygen is red, while barium is the large blue spheres.) Below a critical temperature, the polyhedrons began to twist and slide (arrows).

The Science

To create materials that handle heat well, scientists are exploring how vibrations within the atomic structure carry heat. Atomic vibrations used to remove heat usually are limited by the speed of sound. A new observation may have shattered that limit. A team of scientists observed particles, called phasons, moving faster than the speed of sound that carry heat. The phasons use a pattern of motion in which atoms rearrange themselves, allowing heat to move faster.

The Impact

The observed supersonic phasons enhance the thermal conductivity in insulators by 20% at room temperature, opening new paradigms for the design of a wide variety of electronics. Without the usual limits of heat transport, these supersonic phason signals could enable a new type of thermal circuit breakers.

Summary

To improve the thermal properties of materials, scientists are working to control the flow of heat carried by the vibrations of crystal lattices separately from the heat carried by electrons. Usually, it is assumed that vibrations of crystal lattices, called phonons, cannot move faster than the speed of sound. Polyhedra of atoms can also rearrange themselves. Particles related to such rearrangements that change the movement of waves in the crystal structure are called phasons. Phasons have been challenging to measure. Now scientists at Oak Ridge National Laboratory have used neutron scattering to reveal the formation of supersonic phasons in a piezoelectric mineral fresnoite (Ba2TiSi2O8). Scientists did not know where to find the phason signal. First, the team used pulses of neutrons from the Spallation Neutron Source to determine where to look for the phasons. Then, focusing on the identified region, they did a more detailed analysis using a constant flux of neutrons from the High Flux Isotope Reactor. The neutrons had a narrow range of energy and, when scattered by the material, provided higher resolution data, revealing the presence of supersonic phasons. With this knowledge, scientists may be able to control the transport of lattice energy beyond the limits of phonons.

Contact

Michael Manley
Oak Ridge National Laboratory
manleyme@ornl.gov

Funding

This work was supported by the Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences. This work utilized the High Flux Isotope Reactor and the Spallation Neutron Source, DOE Office of Science user facilities.

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