discovery by scientists at the Department of Energy's Oak Ridge National
Laboratory supports a century-old theory by Albert Einstein that explains
how heat moves through everything from travel mugs to engine parts.
transfer of heat is fundamental to all materials. This new research,
published in the journal Science,
explored thermal insulators, which are materials that block transmission
saw evidence for what Einstein first proposed in 1911 -- that heat
energy hops randomly from atom to atom in thermal insulators," said
Lucas Lindsay, materials theorist at ORNL. "The hopping is in addition
to the normal heat flow through the collective vibration of atoms."
random energy hopping is not noticeable in materials that conduct heat
well, like copper on the bottom of saucepans during cooking, but may be
detectable in solids that are less able to transmit heat.
observation advances understanding of heat conduction in thermal
insulators and will aid the discovery of novel materials for
applications from thermoelectrics that recover waste heat to barrier
coatings that prevent transmission of heat.
and his colleagues used sophisticated vibration-sensing tools to detect
the motion of atoms and supercomputers to simulate the journey of heat
through a simple thallium-based crystal. Their analysis revealed that
the atomic vibrations in the crystal lattice were too sluggish to
transmit much heat.
predictions were two times lower than we observed from our experiments.
We were initially baffled," Lindsay said. "This led to the observation
that another heat transfer mechanism must be at play."
that the second heat transfer channel of random energy hopping exists
will inform researchers on how to choose materials for heat management
applications. This finding, if applied, could drastically reduce energy
costs, carbon emissions and waste heat.
useful materials, such as silicon, have a chemically bonded latticework
of atoms. Heat is usually carried through this lattice by atomic
vibrations, or sound waves. These heat-bearing waves bump into each
other, which slows the transfer of heat.
thallium-based material we studied has one of the lowest thermal
conductivities of any crystal," Lindsay said. "Much of the vibrating
energy is confined to single atoms, and the energy then hops randomly
through the crystal."
the sound waves and the heat-hopping mechanism first theorized by
Einstein characterize a two-channel model, and not only in this
material, but in several other materials that also demonstrate ultralow
conductivity," said ORNL materials scientist David Parker.
now, heat-hopping may only be detectable in excellent thermal
insulators. "However, this heat-hopping channel may well be present in
other crystalline solids, creating a new lever for managing heat," he
study's lead coauthor was Saikat Mukhopadhyay, a former postdoctoral
research associate at ORNL and currently a National Research Council
research associate at the U.S. Naval Research Laboratory.
Ridge National Laboratory. Note:
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