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Thermoelectric properties of thiospinels In1-x@xIn2S4-yTey

Subject Area Experimental Condensed Matter Physics
Solid State and Surface Chemistry, Material Synthesis
Term from 2020 to 2024
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 441856638
 
Final Report Year 2024

Final Report Abstract

The In0.84 0.16In2S4-yTey, In0.78 0.22In2S4-yTey and In0.67 0.33In2S4-yTey (y = 0.1, 0.2, 0.3) samples were synthesized. The solubility of tellurium in such thiospinels was found to be limited to y ≤ 0.2. The complex studies of physical properties of these materials involving diverse methods revealed them to be n-type semiconductors with moderate energy band gaps as well as to be characterized by reduced electrical and thermal conductivities in comparison to the pristine binary In-S compounds. All these resulted in enhancement of the thermoelectric efficiency by a factor of approximately two. Measuring Hall effect, we have shown that such changes are mainly related to the increase of charge carrier concentration and their mobility. To analyse the phonon scattering mechanisms, which are dominant factors influencing thermal transport, the optothermal Raman technique was involved. This allowed us to distinguish between normal-, umklapp- three phonon as well as four phonon processes, which are beneficial with respect to the needed reduction of thermal conductivity. Our studies have shown that strong structural disorder and ‘rattling’ effect in indium thiospinels are additional factors contributing to the improvement their thermoelectric efficiency. To establish the optothermal Raman technique as powerful tool in the clarification of the involvement phonon processes in thermal transport, we tested it on synthetically grown (FeS2, In2Te3, BiFeO3) and on natural (FeS2, PbS, PbCuSbS4) crystals. Performing again complex studies involving thermal and electrical transport, specific heat capacity, thermal expansion measurements combined with quantum mechanical theoretical simulations we provided new insights in the understanding of charge carriers and phonon scattering mechanisms in these, at the first glance, well established materials. The obtained results, developed approaches and methodologies coming from the activities within this project are opening some new horizons in the solid state physics and chemistry as well as in the general material science.

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