New insights bolster Einstein's idea about how heat moves through solids

June 28, 2018, Oak Ridge National Laboratory
New research about the transfer of heat--fundamental to all materials--suggests that in thermal insulators, heat is conveyed by atomic vibrations and by random hopping of energy from atom to atom. This finding by Oak Ridge National Laboratory could introduce new materials as thermal energy barriers to drastically reduce energy costs, carbon emissions and waste heat. Credit: Jill Hemman and Adam Malin/Oak Ridge National Laboratory, US Dept. of Energy

A 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.

The transfer of is fundamental to all materials. This new research, published in the journal Science, explored , which are materials that block transmission of heat.

"We saw evidence for what Einstein first proposed in 1911—that heat 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 ."

The 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.

This 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.

Lindsay 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 in the crystal lattice were too sluggish to transmit much heat.

"Our 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."

Knowing 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 .

Many 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.

"The 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."

"Both 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 scientist David Parker.

For 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 said.

The 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.

Additional coauthors of the paper titled, "Two-channel model for ultralow thermal conductivity of crystalline Tl3VSe4," included ORNL's David S. Parker, Brian C. Sales, Alexander A. Puretzky, Michael A. McGuire and Lucas Lindsay.

Explore further: Very thin film could help manage heat flow in future devices

More information: DOI: 10.1126/science.aar8072 "Two-channel model for ultralow thermal conductivity of crystalline Tl3VSe4" Science (2018). http://science.sciencemag.org/cgi/doi/10.1126/science.aar8072

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7 comments

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etherair
3 / 5 (2) Jun 28, 2018
Filed under "interesting" for now. Perhaps something useful or likely not. Knowledge is good just by being new and true.
ZoeBell
Jun 28, 2018
This comment has been removed by a moderator.
rrwillsj
1 / 5 (1) Jun 29, 2018
Well, I'm not sure how "free" the electrons are. The Laws of Thermodynamics dictates that everything, every event, has a "price" if not a "value".
ZoeBell
Jun 29, 2018
This comment has been removed by a moderator.
milnik
not rated yet Jul 02, 2018
Does science know what is heat and how it arises, and what processes need to take place in matter and energy obtained from matter? How can one draw conclusions about the movement of heat through matter, if he does not understand the concept of heat. You are all rounded up by the story that there are heat conductors that leak different amounts of heat.
Do you know how heat can spill (pass) through matter or through your vacuum? It is necessary to know who causes heat and how it is created and it will be possible to find out everything about it. But if this is not known in vain, there will be all attempts, as many problems can not be solved without knowing the properties and formation of matter.
humy
5 / 5 (1) Jul 02, 2018
Does science know what is heat and how it arises, ...?

yes
milnik
not rated yet Jul 02, 2018
@humy,
Can you describe how science knows what the heat is and how it arises and what is the cause of its appearance.

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