JNCASR research finds unusual wave-like heat transport in crystalline solids

Researchers at the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Bengaluru, have found an unusual way in which heat moves through a crystalline material, a finding that could help in developing more efficient technologies to convert waste heat into electricity.The study, published in the Science Advances journal, examines a copper-based material called TlCu5Se3.The researchers found that, unlike the conventional understanding of heat moving through a crystal, heat in this material is transported predominantly through wave-like behaviour of phonons, which are tiny vibrations that carry heat through a solid.In simple terms, heat in most crystalline materials is understood to move somewhat like particles travelling through a medium. But in TlCu5Se3, the researchers found that the material’s complicated internal structure causes this picture to break down.Copper atoms inside the material are able to move locally, but are confined to specific regions rather than freely travelling through the structure. This creates strong disorder and unusual vibrations in the crystal.Professor Kanishka Biswas, who led the research team, described the material’s structure as a complex, knot-like framework.The restricted movement of copper atoms creates what scientists call strong anharmonicity. Essentially, the atoms do not vibrate in the simple, regular manner expected in an ideal crystal.These vibrations interact strongly with one another, allowing heat to be carried through wave-like coherence between different vibrational modes.This is important because the material has an exceptionally low ability to conduct heat through its lattice. Its lattice thermal conductivity was measured at about 0.3 to 0.2 watts per metre-kelvin between 294 and 673 K. At the same time, it retains good electrical transport properties, which are both important for a good thermoelectric material.Bring Anaimangalam Chola-era copper plates to Tamil Nadu for public display, say political party leadersThermoelectric materials can convert a temperature difference directly into electricity. This means they can potentially be used to recover electricity from waste heat produced by industrial machinery, vehicles and other systems.The researchers achieved a thermoelectric figure of merit, or zT, of about 1.42 at 673 K in the original material. By introducing a small number of copper vacancies, they increased this to about 1.7 at the same temperature.The significance of the study, however, goes beyond this particular material.Conventional approaches often try to reduce heat conduction by making ions highly mobile, but excessive movement can destabilise a material. Here, the researchers show that ions can instead be kept within confined regions while still creating the strong vibrations needed to suppress heat transport.This could provide a new design strategy for thermoelectric materials, materials that conduct electricity well but prevent heat from passing through easily.“While this could aid in mid-temperature range energy conversion, such as steel and thermal power plants, and even in car and bike exhaust pipes. Specifically, it can help data centres which produce a lot of waste heat. This kind of material, which is an extremely low thermal conductor and has a high thermoelectric figure of merit, can convert the waste heat from data centres into electricity,” explained Biswas.He also added that such a material can also be used in quantum technologies.“One of the main concerns when it comes to quantum technologies is fear of losing information due to thermal decoherence. Ultra-low thermal conductors like TlCu5Se3 can be used as a shield or a platform for quantum technology,” he explained.The research team included PhD students Sayantoni Choudhury and Animesh Bhui.

Source: Deccan Herald