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 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.
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.
Oak Ridge National Laboratory
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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Nature Communications 9, 1823 (2018). [DOI: 10.1038/s41467-018-04229-1]