Faculty Publications
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Item High Thermoelectric Performance of Co-Doped Tin Telluride Due to Synergistic Effect of Magnesium and Indium(American Chemical Society service@acs.org, 2017) Bhat, D.K.; Shenoy, U.S.Thermoelectric (TE) materials are considered go-to materials lately in addressing the worldwide energy crisis. We report a study on the effect of co-doping of magnesium and indium in lead-free SnTe both experimentally and theoretically. We show how the resonant levels introduced by indium increase the Seebeck coefficient at lower temperatures and how magnesium enhances the Seebeck at higher temperatures by opening the band gap and decreasing the energy difference between the light and heavy hole valence sub-bands. Synergistically, the effects of band engineering lead to the co-doped sample having high thermoelectric figure of merit (ZT) over a wide range of temperature and record a high power factor of ?42 ?W cm-1 K-2 for SnTe based materials. For the very first time we show the effect of site occupied by the dopant on the electronic structure of the material. The resulting high ZT of 1.5 at 840 K makes SnTe a very suitable material for thermoelectric applications. (Graph Presented). © 2017 American Chemical Society.Item Enhanced Bulk Thermoelectric Performance of Pb0.6Sn0.4Te: Effect of Magnesium Doping(American Chemical Society service@acs.org, 2017) Shenoy, U.S.; Bhat, D.K.Thermoelectric (TE) materials are promising in the context of renewable power generation as they can directly convert waste heat into electricity. Although PbTe is the best known TE material, its use is not encouraged due to concerns of environmental toxicity of lead. A combination of modified self-propagating high-temperature synthesis (SHS) and field-assisted sintering technique (FAST) is employed for the very first time to synthesize a solid solution of PbTe and SnTe. We show that doping of Pb0.6Sn0.4Te with Mg breaks crystal mirror symmetry and opens up band gap. This results in suppression of bipolar diffusion. Also the increase in degeneracy of valence sub-bands improves Seebeck coefficient. Both these synergistically leads to remarkable enhancement in figure of merit ZT (?2 at 840 K) and ZTavg (?1.2 between 500 and 840 K) rendering it into high-performance thermoelectric material by successfully engineering electronic structure. Most importantly, the ZT here is comparable to that of Mg-doped PbTe but has lesser lead content and hence is more environment friendly. The most probable configuration of Pb0.6Sn0.4Te was also determined for the very first time using site occupancy disorder (SOD) technique. © 2017 American Chemical Society.Item Enhanced thermoelectric performance of bulk tin telluride: Synergistic effect of calcium and indium co-doping(Elsevier Ltd, 2018) Bhat, D.K.; Shenoy, S.SnTe based materials are considered recently as a lead-free replacement of the well-known PbTe based thermoelectric (TE) materials in addressing the energy crisis worldwide. Herein we report both experimental and theoretical study on the effect of co-doping of calcium and indium on electronic structure and TE properties of SnTe. We show that the resonant levels introduced by indium and band gap opening caused by calcium, valence band convergence induced by both calcium and indium, synergistically increases the Seebeck coefficient for a wide range of temperatures. The co-doped SnTe with a high ZT of ?1.65 at 840 K and record high power factor of ?47 ?Wcm?1K?2 for SnTe based materials make it a promising material for TE applications. © 2018 Elsevier LtdItem Tuning the Photocatalytic Activity of SrTiO3 by Varying the Sr/Ti Ratio: Unusual Effect of Viscosity of the Synthesis Medium(American Chemical Society service@acs.org, 2018) Bantawal, H.; Shenoy, U.S.; Bhat, D.K.SrTiO3 nanostructures were successfully synthesized in various alcohols as cosolvent as well as surfactant by a facile solvothermal method. The as-synthesized catalysts were characterized by X-ray diffraction technique, scanning electron microscopy, energy-dispersive X-ray analysis, Brunauer-Emmett-Teller analysis, diffuse reflectance spectroscopy, and photoluminescence spectroscopy. The possible formation mechanism of SrTiO3 in the presence of these alcohols is discussed, and the effect of these alcohols on the structure, Sr/Ti atomic ratio, and optical properties is related to the photocatalytic activity. First principles calculations were made use of to determine the effect of defects on the electronic structure and the band gap. The photocatalytic activity of these catalysts was evaluated by taking methylene blue as a model pollutant under visible light irradiation. It was found that the photocatalytic activity of ethanol-mediated SrTiO3 was found to be higher than the other samples because of the synergistic effect of high surface area and lesser defects. © 2018 American Chemical Society.Item Band Engineering of SrTiO3: Effect of Synthetic Technique and Site Occupancy of Doped Rhodium(American Chemical Society service@acs.org, 2018) Shenoy, U.S.; Bantawal, H.; Bhat, D.K.It is well known that doping of Rh into the SrTiO3 lattice introduces 4d donor levels within the band gap, which causes reduction in the gap and extends the photocatalytic activity to the visible region of the solar spectrum. The mid-gap states formed also act as recombination centers and diminish the efficiency of the material. Herein, we present a combined theoretical and experimental approach to avoid the formation of the so-called acceptor mid-gap states. For the first time, we study the effect of occupancy of Rh in the Sr site. First-principles calculations reveal that mixed occupancies of Rh into Sr and Ti sites lead to the introduction of acceptor levels within the band gap, leading to decrease in photocatalytic efficiency. A facile one-pot solvothermal approach by avoiding high-temperature calcinations is reported to obtain Rh-doped SrTiO3 nanoparticles in Rh3+ states, suppressing the formation of Rh4+ states by directing Rh toward Sr sites. The photocatalytic activity of Rh-doped SrTiO3 nanoparticles is studied in the case of degradation of methylene blue, wherein the 1.0 Rh sample was found to be highly efficient. © 2018 American Chemical Society.Item Electronic structure engineering of tin telluride through co-doping of bismuth and indium for high performance thermoelectrics: A synergistic effect leading to a record high room temperature ZT in tin telluride(Royal Society of Chemistry, 2019) Shenoy, U.S.; Bhat, D.K.The ever increasing demand for alternative clean energy sources has led to intense research towards the optimization of thermoelectric performance of known systems. In this work, we engineer the electronic structure of SnTe by co-doping it with Bi and In. The co-doping not only results in the formation of two different resonance states and a reduced valence band offset, as in the case of previously reported co-doped SnTe, but also leads to opening of the band gap, which otherwise was closed in the case of Bi and In doped SnTe configurations, leading to suppression of bipolar diffusion. The synergistic action of all these effects leads to an increased Seebeck co-efficient throughout the temperature range and a ZTmax of ?1.32 at 840 K. This strategy of co-doping two different resonant dopants resulted in a record high room temperature ZT of ?0.25 at 300 K for SnTe based materials. This work suggests that appropriate combination of dopants to engineer the electronic structure of a material can lead to unpredictable results. © 2019 The Royal Society of Chemistry.Item Porous Graphene Wrapped SrTiO3 Nanocomposite: Sr-C Bond as an Effective Coadjutant for High Performance Photocatalytic Degradation of Methylene Blue(American Chemical Society service@acs.org, 2019) Bantawal, H.; Sethi, M.; Shenoy, U.S.; Bhat, D.K.Porous graphene-SrTiO3 (PGST) composite prepared by a facile solvothermal method was tested for its photocatalytic activity in degradation of methylene blue (MB) dye. First-principles density functional theory calculations were also carried out to study the effect of nanocomposite formation on the electronic structure and density of states. The combined experimental and theoretical study gave insights regarding the formation of the Sr-C bond which enhanced the charge transport, effectively separating the charge carriers and reduced their recombination rate. The formation of PGST nanocomposite favorably tuned the electronic structure with decreased band gap due to introduction of the hybridized states extending the absorption to the visible region of electromagnetic spectrum. The microscopy studies revealed loofah like PG wrapped SrTiO3 nano structures with contusions providing high surface area facilitating adsorption of MB dye. Degradation of ?92% was obtained by 7.5 PGST in 120 min with high cyclic stability indicating its suitability as an efficient photocatalyst for the treatment of pollutants. © 2019 American Chemical Society.Item Vanadium-Doped SrTiO3 Nanocubes: Insight into role of vanadium in improving the photocatalytic activity(Elsevier B.V., 2020) Bantawal, H.; Shenoy, U.S.; Bhat, D.K.SrTiO3 based materials have been gaining attention recently in the field of photocatalysis due to their tunable electronic structure. Herein, we employ a facile one pot solvothermal approach for the synthesis of V doped SrTiO3 nanocubes. First principles theoretical calculations reveal that the 3 'd' dopant level introduced by V reduces the band gap and extends the absorption to the visible region of spectrum. The occupancy of Ti site by V introduces dopant states overlapping with the conduction band, eliminating the formation of mid gap recombination centres. Photocatalytic experimental studies on degradation of methylene blue dye reveals the material to be an excellent photocatalyst with high photocorrosion resistance and cyclic stability. In addition, the material is also predicted to be a potential thermoelectric material. © 2020 Elsevier B.V.Item SnTe thermoelectrics: Dual step approach for enhanced performance(Elsevier Ltd, 2020) Bhat, D.K.; Shenoy, U.S.Doping of SnTe to achieve desirable properties has been a wide spread approach in the recent past to enhance its thermoelectric performance. Herein, we apply a dual approach: Pb doping for reduction of thermal conductivity and Zn doping for improving the power factor. The theoretical prediction of enhanced Seebeck due to increase in the band gap, introduction of the resonance levels by Zn and dominance of the heavy hole valence band, is realized experimentally as improved power factor throughout the temperature range. The accompanying reduction in the thermal conductivity by co-doping Pb and Zn leads to a record high room temperature figure of merit, ZT of 0.35 (@ 300K) and ZT of 1.66 at 840 K. The ZTaverage of ?0.9 with 300 K as cold end and 840 K as hot end sets a new record for SnTe based materials. © 2020 Elsevier B.V.Item Resonance levels in GeTe thermoelectrics: Zinc as a new multifaceted dopant(Royal Society of Chemistry, 2020) Bhat, D.K.; Shenoy, U.S.Recently doping has been widely used in enhancing the thermoelectric properties of lead-free GeTe. But much of the work has been concentrated on carrier concentration tuning or phonon scattering. Until now, only indium has been reported to be the best resonant dopant in cubic GeTe. Herein, for the first time we introduce zinc as a resonant dopant to the cubic GeTe family. We show that zinc in GeTe not only introduces resonance states but also increases the band gap and raises the heavy hole valence band above the light hole valence band leading to enhanced Seebeck values. This multifunctional dopant incorporation in GeTe leads to enhanced transport properties as predicted by Boltzmann transport properties calculations based on first principles density functional theory electronic structure calculations. This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
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