Faculty Publications
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Item Resonance states and hyperconvergence induced by tungsten doping in SnTe: Multiband transport leading to a propitious thermoelectric material(Elsevier Ltd, 2022) Shenoy, U.S.; D, G.K.; Bhat, D.K.Discovery of dopants which can engineer the electronic structure of the thermoelectric materials beneficially to improve the figure of merit has been receiving a lot of attention. In this work, we study one such unique dopant, tungsten in SnTe by implementing first principles density functional theory approach. We predict that tungsten is a n-type resonant dopant which not only increases the band gap but causes convergence of valence sub-bands leading to increased Seebeck co-efficient due to increase in the effective mass and decrease in the bipolar conduction. We show for the first time, the introduction of hyperconvergence in the conduction sub-bands, a feature which was observed only in valence bands of SnTe and GeTe. In addition to the above features, it also introduces multiple electronic valleys near the Fermi level excluding the use of a co-dopant to exploit the benefits of the electronic structure engineering. A maximum ZT of ~1.61 theoretically achieved by tuning the chemical potential at 800 K makes this material worth being explored experimentally. © 2022 Elsevier B.V.Item Asymmetric Thermoelectric Performance Tuning in Low-Cost ZrFexNi1-xSb Double Half-Heusler Materials(American Chemical Society, 2023) Kahiu, J.N.; Kihoi, S.K.; Kim, H.; Shenoy, U.S.; Bhat, D.K.; Lee, H.S.The new paradigm for increasing the commercial viability of thermoelectric materials in the energy sector is the theoretical prediction and subsequent experimental validation and optimization of cheaper and inherently more efficient compositions. Herein, the experimental validation of the recently theoretically predicted ZrFe0.50Ni0.50Sb double half-Heusler and the ability to intrinsically tune this system to optimized p- or n-type materials by varying the Fe/Ni ratio in the synthesized ZrFexNi1-xSb (x = 0.35-0.65) samples are demonstrated. The samples are synthesized by arc melting, hot pressing, and annealing. Subsequent microstructural analysis confirms the crystallization of the ZrFexNi1-xSb into the half-Heusler structure and reveals that the variation of the Fe/Ni ratio favors the Ni-rich side. Consequently, the best p-type x = 0.55 and n-type x = 0.35 samples exhibit higher power factor values stemming from an increased carrier concentration, higher density of state effective mass, and suppressed bipolar conduction, as indicated by the Hall data analysis and density functional theory simulations. The additional lattice disorders introduced by varying the Fe/Ni ratio suppress the thermal conductivity and increase the microhardness of the n-type samples. The ZrFe0.35Ni0.65Sb and ZrFe0.55Ni0.45Sb samples achieve maximum zTs of ∼0.43 and 0.06, respectively, which is a great improvement over the ∼0.001 value of the ZrFe0.50Ni0.50Sb sample. These results highlight the viability of tuning the performance of double half-Heuslers on the doubly doped site. They will be instrumental in demonstrating the feasibility of developing low-cost double half-Heusler materials with better intrinsic and highly tunable properties. © 2023 American Chemical Society.Item Enhanced photoresponse and efficient charge transfer in porous graphene-BaTiO3 nanocomposite for high performance photocatalysis(Elsevier Ltd, 2023) Bhat, D.K.; Bantawal, H.; Uma, U.; Shenoy, U.S.Porous graphene-BaTiO3 (PGBT) nanocomposite was synthesized by a simple one pot solvothermal method and its photocatalytic activity was evaluated by studying its efficiency in degrading methylene blue (MB) dye under visible light. The combination of experimental and theoretical analysis revealed enhanced photocatalytic activity of the PGBT composite, which could be attributed to (i) the interaction of BaTiO3 nanoparticles with PG sheets via Ba–C bond, (ii) reduced band gap due to the introduction of hybridized states leading to increased absorption in visible range and (iii) large surface area which provides more active sites for the efficient adsorption of MB dye. The formation of Ba–C bond proved to be highly advantageous for the efficient transport of photogenerated charge carriers, thereby suppressing the recombination of charge carriers. The synthesized nanocomposite showed three times higher photodegradation efficiency compared to BaTiO3. In addition to this, the composite also showed an excellent cyclic stability indicating its suitability as an effective photocatalyst for the environmental remediation. © 2023 Elsevier B.V.Item Towards achieving an ideal convergence of light and heavy electron conduction bands in SnTe: Insights into copper doping(Elsevier B.V., 2024) Shenoy, U.S.; Bhat, D.K.In recent years, tin telluride has garnered significant attention in the field of thermoelectrics, offering a promising avenue for sustainable ecofriendly conversion of waste heat into electricity. The unique electronic structure of this material makes it a compelling candidate for exploring innovative strategies to enhance its transport properties by employing substitutional doping. Among myriad elements doped, copper has been considered an intriguing candidate due to its ability to lower the thermal conductivity. However, its impact on the electronic structure has not been thoroughly explored till date. Herein, we investigate a nuanced aspect of copper doping, specifically focusing on its impact on tuning the electronic structure of SnTe. Significantly, our findings reveal a novel dimension to copper doping, showcasing its potential to enhance n-type performance in SnTe through the near-perfect convergence of its conduction bands - a feature not observed when doped in GeTe. We also shed the light on improvement of the p-type performance by means of valence band convergence and increased band gap. Furthermore, we reveal that copper doping allows the contribution of low-lying bands in SnTe to participate in transport, ensuring a higher Seebeck coefficient across the entire temperature range. Overall, this work provides a panoramic view of role of copper in improving the Seebeck co-efficient of SnTe making it a potential lead-free material for several thermoelectric applications. © 2024 Elsevier B.V.