Discovery contradicts physics principle that heat always moves faster as pressure increases

A discovery by UCLA researchers and their colleagues on heat transfer through materials contradicts the conventional wisdom that heat always moves faster as pressure increases.

A boron arsenide crystal between two diamonds in a controlled chamber with thermal energy under extreme pressure. Photo: The H-Lab/UCLA

That conventional wisdom held true in observations and scientific experiments involving materials such as gases, liquids and solids.

However, the research team observed that with boron arsenide, heat started to move slower under extreme pressure, suggesting a possible interference caused by the ways heat vibrates through a structure as pressure mounts.

The scientists found that boron arsenide, which has been viewed as a promising material for heat management and advanced electronics, has a unique property.

After reaching a pressure hundreds of times greater than the pressure found at the bottom of the ocean, boron arsenide's thermal conductivity begins to decrease.

The results suggest that other materials might experience the same phenomenon under extreme conditions and may lead to novel materials that could be developed for smart energy systems.

"This finding shows that the general rule of pressure dependence starts to fail under extreme conditions," said study leader Yongjie Hu, a mechanical and aerospace engineer at UCLA.

"We expect that this study will not only provide a benchmark for potentially revising the current understanding of heat movement, but could impact established modeling predictions for extreme conditions, such as those found in the Earth's interior, where direct measurements are not possible."

According to Hu, the breakthrough may lead to a retooling of standard techniques used in shock wave studies. (U.S. National Science Foundation)

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