A material outperforms diamond in thermal conductivity

 Scientists observed that Boron arsenide beats diamond in thermal                   conductivity                                            

The researchers found that boron arsenide exceeded diamond in heat conduction, offering better thermal management for electronics. Scientists have long hailed diamond as nature’s ultimate heat conductor, but that crown may now belong to a synthetic crystal. Researchers at the University of Houston have discovered that boron arsenide (BAs) can surpass diamond in carrying heat, rewriting what physicists thought they knew about thermal conductivity. Boron arsenide has dethroned diamond as the best heat conductor, thanks to refined crystal purity and improved synthesis methods. Now researchers have achieved a major scientific milestone in the study of heat transfer. This discovery could transform next-generation electronics by combining record-breaking thermal conductivity with strong semiconductor properties. Boron arsenide just rewriting the rules of heat conduction and semiconductor design. The new findings overturn long-standing assumptions about thermal conductivity and reveal that boron arsenide (BAs) can conduct heat more effectively than diamond, which has long been considered the benchmark among isotropic materials.

The study is part of a $2.8 million National Science Foundation project led by Bolin Liao at UC Santa Barbara, with contributions from the University of Houston, the University of Notre Dame and UC Irvine. The research also receives partial support from industrial partner Qorvo. The researchers found that high-quality boron arsenide crystals achieved thermal conductivity above 2,100 watts/meter/Kelvin (W/mK) at room temperature, possibly higher than that of diamond. For decades, diamond held the record among isotropic materials, meaning those with uniform properties in all directions. The research team discovered that when BAs crystals are produced with exceptional purity, they can reach thermal conductivity values possibly surpassing diamond itself. The study challenges existing theoretical models and could reshape how scientists think about heat movement through solid materials. The results also point to a promising new semiconductor option for devices which demand advanced thermal management, including smartphones, high-power electronics and data centres.

The finding not only challenges existing theories but could reshape how electronics handle heat. From smartphones to data centers, efficient thermal management is critical for performance and longevity. The discovery could usher in a new era of materials which make chips cooler, faster and long-lasting. “We trust our measurement; our data is correct and that means the theory needs correction,” said Zhifeng Ren, corresponding author and professor in UH’s Department of Physics. “I’m not saying the theory is wrong, but an adjustment needs to be made to be consistent with the experimental data.” By refining raw arsenic and developing improved synthesis methods, the UH-led team created boron arsenide crystals with significantly fewer imperfections. When tested, these high-purity samples demonstrated a remarkable thermal conductivity above 2,100 W/mK, surpassing not only earlier experimental results but also the theoretical ceiling itself. The discovery emerged from a collaboration among the University of Houston's Texas Center for Superconductivity (directed by Ren), the University of California, Santa Barbara, and Boston College.

For years, boron arsenide was theorized to rival diamond’s heat conduction, but experiments consistently fell short. Boron arsenide has intrigued scientists earlier. In 2013, Boston College physicist and study co-author David Broido and colleagues predicted that BAs could theoretically conduct heat as efficiently, or even better, than diamond. However, revised models in 2017 added a complex factor known as four-phonon scattering, which reduced predicted performance to around 1,360 W/mK. This caused many in the field to abandon the idea that BAs could exceed diamond's conductivity. Ren's group, however, suspected the problem wasn't the material's intrinsic ability but the impurities within it. Earlier experimental samples contained defects that limited performance to about 1,300 W/mK, well below the ideal conditions used in theoretical predictions. This achievement confirms that material purity plays a decisive role in heat transfer performance and opens a path toward even more efficient heat-conducting materials.

“We trust our measurement; our data is correct and that means the theory needs correction,” Ren repeated, underscoring how real-world data outpaced the math. Boron arsenide’s advantages stretch far beyond breaking records. It’s not just an exceptional thermal conductor, it’s also a promising semiconductor. The implications of this breakthrough extend far beyond laboratory measurements. Boron arsenide has the potential to revolutionize electronics and semiconductor technology by providing a material which both dissipates heat effectively and performs as a high-quality semiconductor. Its advantages include the following:-

Exceptional thermal conductivity combined with efficient semiconductor behaviour.

Potentially superior electronic performance compared to silicon due to its high carrier mobility, wide band gap and well-matched coefficient of thermal expansion.

Easier and more cost-effective manufacturing compared to diamond, without the need for extreme temperature or pressure.

Although this discovery marks a new frontier, the work is on going. Researchers at the Texas Centre for Superconductivity plan to continue refining their methods, aiming to enhance boron arsenide's performance even further. "This new material, it's so wonderful," Ren said. "It has the best properties of a good semiconductor, and a good thermal conductor, all sorts of good properties in one material. That has never happened in other semiconducting materials." The combination makes it a rare candidate to outperform silicon, the foundation of modern electronics. Its coefficient of thermal expansion is also well-matched for chip integration, making it ideal for next-generation devices. Ren encourages scientists to revisit existing models and challenge theoretical assumptions that may have underestimated materials like BAs. "You shouldn't let a theory prevent you from discovering something even bigger, and this exactly happened in this work," Ren said. The breakthrough could have far-reaching applications in AI hardware, power electronics and high-performance computing, where overheating limits innovation. Still, the researchers say their work is just beginning. The team plans to refine their methods to push BAs’ performance even higher in the future.

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Generate electricity from the cold night sky

 Newly invented device by UC Davis Engineers can generate electricity from the cold night sky  

Engineers at the University of California, Davis (UC Davis) have demonstrated a novel device capable of generating electricity by harvesting the natural cooling of the cold night sky. On clear nights, Earth quietly leaks heat into space. This natural cooling can create a steady energy flow. Their small outdoor engine used the night sky as a cold reservoir, maintained a strong temperature difference overnight, and delivered enough power to run a small fan. The study demonstrates a new way to harvest night time energy using passive physics.

This technology utilizes the principle of radiative cooling, where the Earth continuously leaks heat into space as infrared light on clear nights. The work was led by Dr. Jeremy Munday at the University of California, Davis (UCDavis). His research centres on clean energy photonics and radiative thermal devices. On clear nights, the sky acts as a heat sink that draws energy away through radiative cooling – heat lost to space as infrared light. A sky-facing surface which emits strongly can fall well below the air temperature without pumps or compressors. At night, the radiator cools through a clear band of wavelengths in the atmosphere which leaks heat to space. This band is often called the atmospheric window, a set of infrared colours where the air is most transparent.

The small, outdoor engine uses the night sky as a cold reservoir. The setup effectively maintains a strong temperature difference between its warm ground plate and its cool sky-facing radiator. This temperature difference is enough to power a Stirling engine, an external heat engine which thrives on small temperature gaps. The bottom plate follows soil warmth, which changes through the night compared to the air. This steadiness helps the engine keep turning while the top plate sheds heat to space. In Davis, the setup kept a steady temperature difference of about 18 °F (-7.8 °C) between its warm and cool plates for long stretches. This was enough to run the engine near one turn/second and deliver usable shaft power. “These engines are very efficient when only small temperature differences exist. If you just set it on the table, it’s not going to produce any power on its own,” said Munday. The team reports potential for several watts per square meter using better components. In one trial the device directly turned a fan and, with a small motor attached, also generated a modest electric current.

In experiments conducted in Davis, the device successfully delivered usable shaft power, running near one turn/second and capable of running a small fan. Dry air and clear skies help the radiator shed heat. Humid nights cut the effect because water vapour glows in the same infrared bands the radiator needs to use. Global maps built from NASA’s CERES radiation data show where the down welling infrared from the sky is lowest, which favours larger temperature gaps. Land surface temperatures from MODIS, an Earth-observing instrument, provide the warm side of the picture. NASA’s MODIS land surface temperature product supplies monthly global maps. The strongest potential appears in arid zones and at high, dry elevations where the air is thin and moisture is scarce.

The team reported potential for outputting several watts per square meter with improved components. The group showed air movement near one foot/second in a greenhouse-like temperature setup, enough to circulate CO2 around leaves. The speed aligns with comfort ranges near 0.5 to 0.7 foot/second, according to ASHRAE, the US standards body for building comfort. They also noted airflow rates that approach about 5 cubic feet/minute/person, which appears in ventilation guidance for many public spaces. The figure appears in an official interpretation of ASHRAE 62.1 which shows how designers combine/person and per area outdoor air. Performance can rise if the radiator couples more strongly to the sky and the warm plate couples better to the ground. Tailored coatings and thin film stacks can boost emissivity in the atmospheric window and can reflect sunlight during the day. A vacuum enclosure around the radiator would curb convective heat leaks. Careful seals and lightweight supports make that upgrade realistic. A Stirling engine, an external heat engine which turns a temperature difference into motion using a sealed gas, thrives on small temperature gaps. It uses two pistons and a regenerator to shuttle gas between warm and cool zones so gas expands, then contracts, keeping a flywheel turning. Real machines are limited by Carnot efficiency, the absolute ceiling for any heat engine which depends only on the hot and cold temperatures. The UC Davis setup runs well at low differences because Stirling engines waste little when designed for gentle pressure swings. 

This breakthrough demonstrates a new way to harvest night time energy passively, with the strongest potential appearing in arid zones and at high, dry elevations where air moisture is scarce. Future versions could run in daytime by reflecting sunlight while still radiating heat in the right infrared bands. Stronger thermal contact with soil or water could also amplify the temperature gap without enlarging the radiator. Reducing friction and matching the motor to the torque and speed would lift electrical output. The engine could also use waste heat from farms or factories on the warm side to raise the overall temperature gap without new fuel. Running a fan without a grid connection sounds modest, yet it fills an overlooked need. Greenhouses need steady air movement at night when plants take up CO2 and humidity creeps up. Buildings need gentle flow for comfort, even when heating and cooling systems are idle. A rooftop unit which moves air with no electricity could support health goals while trimming loads after dark. The study’s global maps relied on down welling infrared, the heat the sky sends toward the surface from air and clouds. This value, combined with local ground temperature, sets the ceiling on the temperature gap a radiator can achieve at a given time and place. As with any passive system, output rises and falls with local weather and siting. Shade, wind and surface materials can change the effective temperatures which the engine actually sees.

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