Faculty Publications
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Item Optimized Mn and Bi co-doping in SnTe based thermoelectric material: A case of band engineering and density of states tuning(Chinese Society of Metals, 2021) Kihoi, S.K.; Kahiu, J.N.; Kim, H.; Shenoy, U.S.; Bhat, D.K.; Yi, S.; Lee, H.S.Tin telluride (SnTe) overwhelmingly continues to be studied owing to its promising thermoelectric properties, tunable electronic structure, and its potential as an alternate to toxic lead telluride (PbTe) based materials. In this research, we engineer the electronic properties of SnTe by co-doping Mn and Bi below their individual solubility limit. The First principles density functional theory studies reveal that both Bi and Mn introduce resonance states, thereby increasing the density of states near the Fermi level leading to enhanced Seebeck coefficient. This unique combination of using two resonant dopants to introduce flatter bands is effective in achieving higher performance at lower temperatures manifesting into a large Seebeck value of ?91 ?V/K at room temperature in the present case. Both elements optimally co-doped results in a very high power factor value of ?24.3 ?W/cmK2 at 773 K when compared to other high performance SnTe based materials. A zT of ?0.93 at 773 K is achieved by tuning the proportion of the co-dopants Mn and Bi in SnTe. The hardness value of pristine SnTe was also seen to increase after doping. As a result, synergistic optimized doping proves to be a suitable means for obtaining thermoelectric materials of superior characteristics without the need for heavy doping. © 2021Item Ultralow Lattice Thermal Conductivity and Enhanced Mechanical Properties of Cu and Sb Co-Doped SnTe Thermoelectric Material with a Complex Microstructure Evolution(American Chemical Society, 2022) Kihoi, S.K.; Shenoy, U.S.; Kahiu, J.N.; Kim, H.; Bhat, D.K.; Lee, H.S.SnTe is an exceptionally promising eco-friendly thermoelectric material that continues to draw immense interest as a source of alternative energy recovered from waste heat energy. Here, we investigate the effect of introducing Cu as a single doping element rather than phase separated in SnTe followed by Sb co-doping to tune the lattice thermal conductivity. A microstructure evolution was observed which influences the thermoelectric performance of these SnTe-based materials. An overall power factor of ∼22 μW/cmK2 and an ultralow lattice thermal conductivity of 0.39 W/mK are reported. A maximum ZT of 0.86 is also reported with an all-time record high hardness value of 165 Hv among SnTe-based thermoelectric materials. Through DFT calculations, we show that Cu opens the band gap of SnTe, whereas Sb in the presence of Cu introduces resonance levels and causes band convergence. This kind of enhanced thermoelectric performance is paramount for the application of SnTe in recovery of heat into useful electrical energy. © 2022 American Chemical SocietyItem Pushing the limit of synergy in SnTe-based thermoelectric materials leading to an ultra-low lattice thermal conductivity and enhanced ZT(Royal Society of Chemistry, 2023) Kihoi, S.K.; Shenoy, U.S.; Kahiu, J.N.; Kim, H.; Bhat, D.K.; Lee, H.S.In the era of sustainable and environmentally friendly energy requirements, alternative sources of energy continue to be fervently sought after. Heat recovery into useful electrical energy from waste heat offers a readily available source of energy with humongous potential. Herein, a non-toxic thermoelectric material, SnTe, is explored. Promising thermoelectric performance is also communicated. Introducing Ge as a single dopant is shown for the first time in SnTe-based materials to introduce amorphous Ge (a-Ge) precipitates into the matrix. These act as an auxiliary contributor to the observed ultra-low lattice thermal conductivity of ∼0.33 W m−1 K−1 at 823 K, which is below the reported amorphous limit of SnTe. Bi, which is a known resonant dopant, was further co-doped to fine-tune the electrical properties where a high power factor of ∼25.7 μW cm−1 K−2 is reported. To push the limit of synergy, Sb was added raising the maximum figure of merit ZT to a value of ∼1.1 at 873 K. With co-doping, dual resonance levels are shown which distorts the density of states (DOS) contributing to an increased band effective mass. In conjunction with the introduction of an amorphous phase, co-doping is ascertained as a practical means for the synthesis of high-performance thermoelectric materials for effective waste-heat recovery applications. © 2023 The Royal Society of ChemistryItem Tailoring the Thermoelectric Performance of the Layered Topological Insulator SnSb2Te4 through Bi Positional Doping at the Sn and Sb Cation Sites(American Chemical Society, 2023) Kihoi, S.K.; Shenoy, U.S.; Kahiu, J.N.; Kim, H.; Bhat, D.K.; Lee, H.S.Ongoing research and development focus on emerging thermoelectric materials with enhanced performance, continually making the possibility of waste heat recovery a reality. In this work, we engineer the thermoelectric properties of the layered SnSb2Te4 topological insulators. To date, there is little research reporting on these materials as potential state-of-the-art thermoelectric materials. Thus, there is a need to formulate effective strategies to realize this potential. Since these materials are known to have intrinsically low lattice thermal conductivity, we shift our attention to improving the electrical transport properties. For the first time, positional Bi doping at both the Sn and Sb cation sites is adopted. The aliovalent and isovalent nature of Bi at these sites, respectively, is shown to cause significant improvements in the performance of these layered materials. The electronic band structure of the pure and doped samples, where we considered various occupancies, is studied whereby we reveal the occurrence of band convergence and resonant levels resulting in a high power factor of ∼10.8 μW cm-1 K-2 at 623 K. Overall, a high ZT of ∼0.46 at a relatively lower temperature of 673 K is recorded. The potential of these materials for thermoelectric applications is shown, especially in the case of Bi doping at the Sn cation site. Continued efforts to enhance the thermoelectric performance of these topological insulators are needed for them to gain a substantial competitive edge in comparison to other state-of-the-art thermoelectric materials. © 2023 American Chemical Society.Item Enhanced Electrical, Thermal, and Mechanical Properties of SnTe through Equimolar Multication Alloying for Suitable Device Applications(American Chemical Society, 2024) Kihoi, S.K.; Shenoy, U.S.; Kim, H.; Kahiu, J.N.; Kim, C.M.; Park, K.-I.; Bhat, D.K.; Lee, H.S.With the ever-growing demand for eco-friendly energy sources to mitigate the global rising temperatures, the universal insatiable need for sustainable and efficient energy sources are earnestly being intensively sought after. The ubiquitous heat within, if successfully tapped, is an utterly promising source of energy. To achieve this, a thermoelectric device (TED) is needed. To enhance the conversion efficiency from heat to useful electrical power, we developed a strategy to improve the thermoelectric performance of the materials involved. In this work, equimolar multication alloying (EMMCA) is proposed for the first time and employed to enhance the performance of SnTe-based thermoelectric materials. Beyond the cation’s solubility limit, in situ compositing is observed with an increasing doping ratio, whereby distinct CuInTe2 ternary second phases are dispersed within the SnTe matrix. The electronic properties of the ensuing alloy are significantly enhanced by the resulting carrier concentration modulation and the unique electronic band engineering. A decrease in the thermal transport properties is likewise reported, benefiting from enhanced phonon scattering and diminished electronic contribution. The mechanical properties are also shown to increase with increased alloying. As a result, single-leg TED performance shows substantial output power in comparison with the pristine sample. The outcomes stemming from EMMCA are documented as significantly impactful, contributing to superior overall thermoelectric performance. © 2024 American Chemical Society.