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Diamonds Face Unlikely Competitor For World's Best Thermal Conductors

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Jul 08, 2013 04:03 PM EDT
Diamond
Diamonds have a new competitor in the form of the unlikely cubic boron arsenide when it comes thermal conductivity, a new study shows. (Photo : Reuters)

An unlikely material, cubic boron arsenide, could deliver a thermal conductivity high enough to compete with the costly industry standard currently set by diamond, according to a report in the latest issue of the journal Physical Review Letters.

Known for its brilliance and use in jewelry, diamond is the best-known thermal conductor - a role that grows increasingly important as smaller, faster and more powerful microelectronic devices pose the challenge of removing the heat they generate quickly.

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However, besides being rare and expensive, high quality synthetic diamond is difficult and costly to produce, prompting researchers to search for new materials with ultra-high thermal conductivities, though little headway has been made in recent years.

Now a team of theoretical physicists from Boston College and the Naval Research Laboratory believe they have devised a new method of evaluation they say indicates massive, untapped potential in the unassuming boron arsenide.

The method includes using a recently developed theoretical approach for calculating thermal conductivities they previously tested with a variety of other well-studied materials. Confident in the accuracy of their approach, the team then took a closer look at boron arsenide, whose thermal conductivity has never been measured though it was estimated to be 10 times smaller than diamond's.

In doing so, the team found that the calculated thermal conductivity of cubic boron arsenide is remarkably high, tying with diamond at more than 2,000 Watts per meter per Kelvin at room temperature and exceeding it at higher temperatures.

Unlike metals, where electrons carry heat, diamond and boron arsenide are electrical insulators, meaning heat is carried by vibrational waves of the constituent atoms. The collision of these waves with each other then creates an intrinsic resistance to heat flow.

However, the team was surprised to find an unusual interplay of certain vibrational properties in boron arsenide that lie outside of the guidelines commonly used to estimate the thermal conductivity of electrical insulators. As it turns out, the expected collisions between vibrational waves are far less likely to occur in a certain range of frequencies, during which large amounts heat can be conducted.

"This work gives important new insight into the physics of heat transport in materials, and it illustrates the power of modern computational techniques in making quantitative predictions for materials whose thermal conductivities have yet to be measured," said David Broido, a professor of physics at Boston College.

Going forward, Broido said, the team plans on verifying their discovery via measurement. Should it prove accurate, the discovery could open new opportunities for passive cooling applications using boron arsenide in addition to demonstrating "the important role that such theoretical work can play in providing useful guidance to identify new high thermal conductivity materials."

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