Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
17 results
Search Results
Item Eco-friendly synthesis of porous graphene and its utilization as high performance supercapacitor electrode material(Elsevier Ltd, 2019) Sethi, M.; Bantawal, H.; Shenoy, U.S.; Bhat, D.K.The successful application of porous graphene (PG) is hindered due to the lack of efficient and cost-effective method for its synthesis. Herein, we report a facile and eco-friendly method to produce PG through a low temperature solvothermal method. The structural and morphological characteristics of PG samples were investigated thoroughly. The as synthesized material is found to be a few layers thick (?4–6 layers) with a surface area of 420 m2 g?1 and consisting of hierarchical pores on the surface of the sheets. A high specific capacitance of 666 F g?1 was obtained at a scan rate of 5 mV s?1, apart from longer cyclic stability with 87% retention of initial capacitance value after 10000 cycles for the PG 28 sample. The fabricated supercapacitor displayed an energy density of 26.3 Wh kg?1 and power density of 6120 W kg?1. Density functional theory calculations were also carried out to qualitatively support the enhanced capacitance by providing theoretical insight from electronic structure and density of states of PG. These results open a new avenue for greener synthesis of high-quality PG using environmentally friendly solvents, without the use of toxic chemicals, for excellent supercapacitor performance. © 2019 Elsevier B.V.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 Zn: a versatile resonant dopant for SnTe thermoelectrics(Elsevier Ltd, 2019) Bhat, D.K.; Shenoy, U.S.SnTe-based materials have been receiving increasing heed in the field of thermoelectrics (TEs) because of their tunable electronic structure. Until now, only In and Bi are reported to introduce resonance level in SnTe. In this work, for the very first time, we report Zn as a resonant dopant in SnTe using first-principles density functional theory calculations. We show that the resonant states introduced by Zn raises the heavy hole valence sub-band above light hole valence sub-band leading to both record high room temperature Seebeck coefficient (~127 ?VK?1 at 300 K) and figure of merit, ZT (~0.28 at 300 K) for SnTe-based materials. The transport properties calculated using Boltzmann transport equations predicts Zn-doped SnTe to be a promising TE material, further confirmed by experimental ZTmaximum of ~1.49 at 840 K and ZTaverage of ~0.78 with 300 K and 840 K as cold and hot ends, respectively. © 2019 Elsevier LtdItem Bi and Zn co-doped SnTe thermoelectrics: Interplay of resonance levels and heavy hole band dominance leading to enhanced performance and a record high room temperature: ZT(Royal Society of Chemistry, 2020) Shenoy, U.S.; Bhat, D.K.Lead free SnTe with a tunable electronic structure has become the front runner in eco-friendly thermoelectrics. Herein, we show through first-principles density functional theory calculations that Bi and Zn doping introduces a resonance level in SnTe. The dominance of the heavy hole valence band at room temperature in Bi-Zn co-doped SnTe leads to a record high room temperature ZT of ?0.3 (at 300 K) for SnTe based materials. The increase in the Seebeck coefficient value due to the interaction between the resonance states and formation of the nanoprecipitates leading to an appreciably low lattice thermal conductivity of 0.68 W m-1 K-1 results in a peak ZT of ?1.6 at 840 K. A record high ZTaverage of ?0.86 with 300 K and 840 K as cold and hot ends, respectively, makes Bi-Zn co-doped SnTe a potential material for thermoelectric applications. This strategy of using two resonant dopants, to not only improve the room temperature ZT but also high temperature values, can very well be extended to other systems. This journal is © The Royal Society of Chemistry.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.Item Vanadium-doped BaTiO3 as high performance thermoelectric material: role of electronic structure engineering(Elsevier Ltd, 2020) Shenoy, U.S.; Bhat, D.K.It is well known that thermoelectric (TE) materials are the most sought-after ones to mitigate energy crisis. Development of an efficient non-toxic, economic, abundant, and stable TE material is quite difficult due to its complicated traits. BaTiO3, a perovskite material shows a tremendous potential as a TE material due to its highly tunable electronic structure. Herein, for the first time we report use of dopant to improve the Seebeck coefficient of BaTiO3. We used first-principles density functional theory calculations to study the effect of vanadium doping in BaTiO3, and for the first time, we report that V acts as a resonant dopant in BaTiO3. The study on effect of site occupancy reveals that V in Ba site distorts the density of states below the conduction band by introducing resonance level at the Fermi level. The transport property calculations based on Boltzmann's relation predicts V-doped BaTiO3 to be a potential TE material. The results also provide new insights into development of BaTiO3 as a multifunctional material. © 2020 Elsevier LtdItem Electronic structure engineering of SrTiO3 via rhodium doping: A DFT study(Elsevier Ltd, 2021) Shenoy, U.S.; Bhat, D.K.SrTiO3, with a highly tunable electronic structure has been recently studied for its thermoelectric (TE) properties. Although originally believed to be a poor TE material, doped SrTiO3 has shown considerable improvement in its TE properties. Herein, we study the electronic structure modifications in Rh doped SrTiO3 by varying the dopant site by using first principles density functional theory calculations. Rh acts as a resonant dopant in SrTiO3 by distorting the density of states near the Fermi level. Transport property calculations predict Rh doped SrTiO3 to be a potential TE material. The results reveal both p- and n-type TE material could be developed by devising synthetic technique to direct Rh towards Ti or Sr site, respectively. © 2020 Elsevier LtdItem Vanadium: A Protean Dopant in SnTe for Augmenting Its Thermoelectric Performance(American Chemical Society, 2021) Shenoy, U.S.; Bhat, D.K.In this work, a second n-type resonant dopant in the form of vanadium is introduced in the SnTe thermoelectrics family. The electronic structure simulated using density functional theory calculations revealed that V not only opens the band gap but also causes convergence of both valence and conduction sub-bands. Apart from introducing the resonance levels at the Fermi energy, the unique trait exhibited is the Rashba splitting of the conduction band to introduce multiple valleys. The advantage is the proximity of these features to the Fermi level, which eliminates the need for a co-dopant to harness the benefits. The Boltzmann transport calculations predicted promising transport properties, which showed the dual nature of vanadium, being capable of acting as a p-type as well as an n-type dopant in SnTe with corresponding maximum ZT values of 1.66 and 1.31, respectively, at 800 K, thus making it a highly potential high-performance thermoelectric candidate for future experimental studies. © 2021 American Chemical SocietyItem 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 Optimized electronic performance in half-Heusler Ti-doped NbFeSb materials by stoichiometric tuning at the Fe and Sb sites(Elsevier Ltd, 2022) Kahiu, J.N.; Shenoy, U.S.; Kihoi, S.K.; Kim, H.; Yi, S.; Bhat, D.K.; Lee, H.S.Electronic structure is known to be highly influenced by the site occupancy and the stoichiometry of the material which in turn largely effects the thermoelectric properties. Herein, we present electronic calculations using density functional theory (DFT) of non-stoichiometric Ti doped NbFeSb configuration, showing the effect of the anti-site Fe atoms on the electronic properties, and supporting them with experimental results of the prepared Nb0.8Ti0.2Fe1+xSb1−x samples. The electronic structure of the non-stoichiometric sample shows the introduction of two distinct peaks near the Fermi level by the Fe atoms at the Sb sites. These resonance states are known to cause an increase in the density of states effective mass near the Fermi level, which explains the increase in the Seebeck coefficient in the sample x = 0.03 compared to the sample x = 0.00. In addition, a comparatively higher electrical conductivity is reported from sample x = 0.03, which is attributed to the aliovalent substitution of Sb atoms by Fe atoms. The simultaneous increase in the Seebeck coefficient and electrical conductivity culminates in an increased power factor of ∼50.3 µW/cmK2 at 373 K, which is ∼46% higher than that of samples x = 0.00 and x = 0.05, highlighting the possibility of increasing the power density by stoichiometric variation to achieve the high joule-per-dollar performance of NbFeSb-based TE devices, the relevance of which is also currently emphasized in the quest for commercial viability. © 2021 Elsevier B.V.