The conventional wisdom is that heat always moves faster as pressure increases, but a new physics principle has been found by UCLA researchers.
The common belief has held true in recorded observations and scientific experiments that involve different materials.
The researchers wrote about their discovery in a study. They found a unique property of Boron Arsenide, a material that has been viewed as a promising material for heat management and advanced electronics. After reaching an extremely high pressure that is hundreds of times greater than the pressure found at the bottom of the ocean, theThermal Conductivity of Boron Arsenide decreases.
There might be other materials that experience the same phenomenon. The advance could lead to the development of novel materials that could be used for smart energy systems with built-in pressure windows so that the system only shuts off after reaching a maximum pressure point.
The general rule of pressure dependence is shown to fail under extreme conditions according to the study leader. We expect that this study will provide a benchmark for revising current understanding of heat movement, but it could also impact established modeling predictions for extreme conditions, such as those found in the Earth's interior.
Standard techniques used in shock wave studies may be retooled after the research breakthrough.
Similar to how a sound wave travels through a rung bell, heat travels through most materials. When pressure squeezes closer to the atoms, it allows heat to move through the material faster, atom by atom.
That isn't the case with Boron Arsenide. The research team observed that heat began to move slower under extreme pressure, suggesting a possible interference caused by different ways the heat vibrates through the structure as pressure mounts. Higher-order interactions can't be explained in textbooks.
After a certain pressure range, the thermal conductivity of minerals can reach a maximum. "If applicable to planetary interiors, this may suggest a mechanism for an internal 'thermal window'--an internal layer within the planet where the mechanisms of heat flow are different from those below and above it," says co-author There may be interesting dynamic behavior in the interiors of large planets.
To achieve the extremely high-pressure environment for their heat- transfer demonstrations, the researchers compressed a boron arsenide crystal between two diamonds. They used quantum theory and other advanced techniques to observe and prove the previously unknown phenomenon.
The study's co-lead authors are five mechanical engineering graduate students. The other authors are Kavner and Martin Kunz.
The Anomalous thermal transport under high pressure is described by Suixuan Li and his colleagues.
Journal information: Nature
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