The temperature difference between the hot and cold regions of a thermoelectric device is used to generate a voltage, which allows the device to convert thermal energy into electricity. Neutrons were used by researchers to analyze single crystals of tin sulfide and tin selenide. Their goal was to gain a better understanding of how the conversion process occurs on the atomic scale. They took readings that measured variations that were temperature dependant. According to the findings of the studies, there is a significant correlation between the frequency of atomic vibrations and the structural changes that occur at various temperatures (phonons).

Because of this relationship, the materials transmit heat in a somewhat different manner. Additionally, the study determined the optimal temperatures for the process of energy conversion. In addition to this, it revealed key scientific insights that may now be used to assist researchers in the development of novel materials that have improved thermoelectric performance.

Materials with thermoelectric properties are absolutely necessary for the development of sustainable energy technology. Neutron scattering was the method that the researchers utilized to unearth specifics on the phonon renormalization mechanism. This is the process that is described by quantum mechanics as being responsible for the unusually low thermal conductivity of two different types of thermoelectric materials. The discoveries could assist researchers in the development of materials for thermoelectric devices that are more effective. It will also assist enhance the technology used to convert renewable energy sources.

Thermoelectrics are devices that produce electricity from thermal energy. These technologies are part of the mix of sustainable energy options that can help reduce the effects of climate change. The relatively low efficiency of thermoelectrics and the restricted variety of materials that can be used for their construction both provide significant challenges. In order for scientists to create materials with higher efficiency, they need to have a fundamental understanding of the mechanism that enables ultralow thermal conductivity.

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Researchers from Duke University utilized neutron scattering experiments, in addition to other methods, to investigate the prototypical thermoelectric materials, which were tin (Sn) crystallized with sulfur (S) and selenium (Se) into binaries – SnS and SnSe – in order to solve this age-old scientific conundrum.

At Oak Ridge National Laboratory, advanced neutron scattering instruments can be found at the Spallation Neutron Source and High Flux Isotope Reactor, both of which are user facilities for the Department of Energy (DOE). These instruments were used to measure structural changes and phonon spectra over a wide temperature range, from 150 K to 1050 K. The results showed that there is a transition at 800 K in which the atomic spacings expand in one direction but contract in others.

The measurement of the dynamics also supplied essential information on the drastic reduction in the frequencies of atomic vibrations at the transition, which is accountable for the reduced heat conduction. This reduction is responsible for the fact that heat conduction is reduced. The research also suggests that the observed phonon behavior could be present in a great number of other materials with similar phase transitions. These materials include halide perovskites, oxide ferroelectrics, or thermoelectrics near instabilities. If confirmed, this would significantly broaden the pool of possibilities for energy conversion materials.

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