Discover the atomic mechanism underlying heat transport in thermoelectric materials
Thermoelectric devices convert thermal energy into electricity by generating a voltage from the temperature difference between hot and cold parts of a device. To better understand how the conversion process occurs at the atomic scale, the researchers used neutrons study single crystals of tin sulfide and tin selenide. They measured changes that depended on temperature. The measurements revealed a strong correlation between the evolution of the structure at certain temperatures and the frequency of the atomic vibrations (phonons). This relationship affects how materials conduct heat. Research has identified ideal temperatures for energy conversion. It also provided basic scientific knowledge that can help researchers design new materials for better thermoelectric performance.
Thermoelectric materials are important for clean energy technologies. Using neutron scattering, the researchers unveiled the details of the phonon renormalization mechanism. It is the process of quantum mechanics that explains the very low thermal conductivity of two typical thermoelectric materials. The results could allow researchers to design materials for more efficient thermoelectric devices. It will also help advance renewable energy conversion technologies.
Thermoelectrics convert thermal energy into electricity. They are part of the mix of clean energy technologies that can mitigate the impact of climate change. One of the main challenges of thermoelectricity is their relatively low efficiency and the limited number of materials available. To design more efficient materials, scientists need a fundamental understanding of the mechanism enabling ultra-low thermal conductivity. To solve this long-standing scientific puzzle, researchers at Duke University used neutron scattering experiments, supplemented by other techniques, to probe the archetypical thermoelectric material, tin (Sn) crystallized with sulfur ( S) and selenium (Se) into binary – SnS and SnSe.
Using advanced neutron scattering instruments at Spallation neutron source and High Flux Isotope Reactor, Department of Energy (DOE) user facilities at Oak Ridge National Laboratory, structural changes and phonon spectra were measured over a wide temperature range from 150 K to 1050 K, revealing a transition to 800 K where the atomic spacings expand in one direction but contract. at the others. The dynamics measurement also provided key insights into the dramatic reduction in atomic vibration frequencies at the transition, which is responsible for the reduced heat conduction. The work also suggests that the observed phonon behavior could be present in many other materials with similar phase transitions, such as halogenated perovskites, ferroelectric oxides or near-instability thermoelectrics, greatly expanding the pool of possibilities for materials. of energy conversion.
Neutron scattering data collection and analysis, sample synthesis, and first-principles theory simulations were supported by DOE’s Office of Science, Division of Basic Energy Sciences, materials and engineering. The research included the use of the Spallation Neutron Source, High Flux Isotope Reactor, Center for Nanophase Materials Science and National Center for Scientific Computing for Energy Research, all user facilities of the Office of Science from the DOE.