Crystals and glasses have opposite heat-conduction properties, which play a pivotal role in a variety of technologies. These range from the miniaturization and efficiency of electronic devices to waste-heat recovery systems, as well as the lifespan of thermal shields for aerospace applications.
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In research published ... in the Proceedings of the National Academy of Sciences, Simoncelli and his collaborators ... predicted the existence of a material with hybrid crystal-glass thermal properties, and a team of experimentalists ... confirmed it with measurements.
The first of its kind, this material was discovered in meteorites and has also been identified on Mars. The fundamental physics driving this behavior could advance our understanding and design of materials that manage heat under extreme temperature differences ...
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Thermal conduction depends on whether a material is crystalline, with an ordered lattice of atoms, or glassy, with a disordered, amorphous structure, which influences how heat flows at the quantum level–broadly speaking, thermal conduction in crystals typically decreases with increasing temperature, while in glasses it increases upon heating.
In 2019, Simoncelli, Nicola Marzari, and Francesco Mauri derived a single equation that captures the opposite thermal-conductivity trends observed in crystals and glasses—and, most importantly, also describes the intermediate behavior of defective or partially disordered materials, such as those used in thermoelectrics for waste-heat recovery, perovskite solar cells, and thermal barrier coatings for heat shields.
Using this equation, they investigated the relationship between atomic structure and thermal conductivity in materials made from silicon dioxide, one of the main components of sand. They predicted that a particular “tridymite” form of silicon dioxide, described in the 1960s as typical of meteorites, would exhibit the hallmarks of a hybrid crystal-glass material with a thermal conductivity that remains unchanged with temperature. ...
That led the team to the experimental groups of Etienne Balan, Daniele Fournier, and Massimiliano Marangolo in France, who obtained special permission from the National Museum of Natural History in Paris to perform experiments on a sample of silica tridymite carved from a meteorite that landed in Steinbach, Germany, in 1724. Their experiments confirmed their predictions: meteoric tridymite has an atomic structure that falls between an orderly crystal and disordered glass, and its thermal conductivity remains essentially constant over the experimentally accessible temperature range of 80 K to 380 K.
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In this new PNAS paper, Simoncelli employed machine-learning methods to overcome the computational bottlenecks of traditional first-principles methods and simulate atomic properties that influence heat transport with quantum-level accuracy. ...