Faculty Publications
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Item Evolutionary algorithm based structure search for hard ruthenium carbides(Institute of Physics, 2015) Harikrishnan, G.; Ajith, K.M.; Chandra, S.; Valsakumar, M.C.An exhaustive structure search employing evolutionary algorithm and density functional theory has been carried out for ruthenium carbides, for the three stoichiometries Ru1C1, Ru2C1 and Ru3C1, yielding five lowest energy structures. These include the structures from the two reported syntheses of ruthenium carbides. Their emergence in the present structure search in stoichiometries, unlike the previously reported ones, is plausible in the light of the high temperature required for their synthesis. The mechanical stability and ductile character of all these systems are established by their elastic constants, and the dynamical stability of three of them by the phonon data. Rhombohedral structure is found to be energetically the most stable one in Ru1C1 stoichiometry and hexagonal structure , the most stable in Ru3C1 stoichiometry. RuC-Zinc blende system is a semiconductor with a band gap of 0.618 eV while the other two stable systems are metallic. Employing a semi-empirical model based on the bond strength, the hardness of RuC-Zinc blende is found to be a significantly large value of ?37 GPa while a fairly large value of ?21GPa is obtained for the RuC-Rhombohedral system. The positive formation energies of these systems show that high temperature and possibly high pressure are necessary for their synthesis. © 2015 IOP Publishing Ltd.Item Pressure-induced variation of structural, elastic, vibrational, electronic, thermodynamic properties and hardness of Ruthenium Carbides(Elsevier Ltd, 2016) Harikrishnan, H.; Ajith, K.M.; Natarajan, S.; Chandra, S.; Mundachali Cheruvalath, V.Three of the five structures obtained from the evolutionary algorithm based structure search of Ruthenium Carbide systems in the stoichiometries RuC, Ru2C and Ru3C are relaxed at different pressures in the range 0-200 GPa and the pressure-induced variation of their structural, elastic, dynamical, electronic and thermodynamic properties as well as hardness is investigated in detail. No structural transition is present for these systems in this pressure range. RuC-Zinc blende is mechanically and dynamically unstable close to 100 GPa. RuC-Rhombohedral and Ru3C-Hexagonal retain mechanical and dynamical stability up to 200 GPa. For all three systems the electronic bands and density of states spread out with pressure and the band gap increases with pressure for the semiconducting RuC-Zinc blende. From the computed IR spectrum of RuC-Zinc blende at 50 GPa it is noted that the IR frequency increases with pressure. Using a semi-empirical model for hardness it is estimated that hardness of all three systems consistently increases with pressure. The hardness of RuC-Zinc blende increases towards the superhard regime up to the limiting pressure of its mechanical stability while that of RuC-Rhombohedral becomes 30 GPa at the pressure of 150 GPa. © 2016 Elsevier Ltd. All rights reserved.Item Bimetallic nanoparticles grafted ZnO hierarchical structures as efficient visible light driven photocatalyst: An experimental and theoretical study(Elsevier B.V., 2021) Shenoy, S.; Tarafder, K.; Sridharan, K.Bimetallic nanoparticles (NPs) exhibiting novel properties due to synergy between the individual elements have sparkled significant interest as a co-catalyst in enhancing the photocatalytic efficiency of semiconductor materials. Here, we report the photocatalytic activity of NiAg NPs embedded on hierarchical ZnO structures (NiAg-ZnO). Structural and morphological investigations through X-ray diffraction and scanning electron microscopy confirmed the formation of NiAg-ZnO. UV-Vis diffuse reflectance spectroscopy revealed the decrease in the bandgap energy of NiAg-ZnO (2.65 eV) in comparison to pristine ZnO (3.1 eV). Interestingly, the rate of photodegradation of methylene blue and rhodamine B dye molecules under visible light irradiation are two to three times enhanced with NiAg-ZnO in comparison to Ag-ZnO. Enhanced visible light absorption and effective charge separation due to the synergistic metal-semiconductor interface formed by the embedment of NiAg bimetallic NPs on ZnO led to the improved photocatalytic activity. Experimental results are further confirmed through the first principle electronic band structure calculations. © 2021Item Graph representational learning for bandgap prediction in varied perovskite crystals(Elsevier B.V., 2021) Omprakash, P.; Manikandan, B.; Sandeep, A.; Shrivastava, R.; Viswesh, P.; Bhat Panemangalore, D.B.Perovskites are an important class of materials that are actively researched for applications in solar cells and other optoelectronic devices due to their ease of fabrication and tuneable bandgaps. High throughput computational techniques like Density Functional Theory (DFT) and Machine Learning (ML) are viable methods to accelerate discovery of new perovskite materials with favourable properties. ML specifically is faster and requires lesser computational power. We recognized the importance of having robust datasets for ML and hence collated a dataset of varied perovskite structures along with their indirect bandgaps. We employed a graph representational learning technique and trained a model that predicted bandgaps for all types of perovskites. The model has a mean absolute error of 0.28 eV and can predict bandgap in a few milliseconds. The metric of generalization gap is introduced to quantify the performance of ML models. This metric will help in building more generalized models that can predict properties for novel materials. Furthermore, we believe that these computational techniques should be user-friendly to those less experienced in the field. Hence, for researchers unacquainted with DFT or ML, we built a pipeline that abstracts the specific processes. This makes it easier for material scientists to quickly screen viable inorganic perovskite compounds allowing them to synthesize and experiment on the more promising compounds. © 2021 Elsevier B.V.Item Exploring the potential role of quercetin in corrosion inhibition of aluminium alloy 6063 in hydrochloric acid solution by experimental and theoretical studies(Taylor and Francis Ltd., 2022) Kumari, D.; Venugopal, P.P.; Reena Kumari, P.D.; Chakraborty, D.Quercetin was evaluated as corrosion inhibitor for AA6063 in 0.5 M HCl solution by employing weight-loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Analysis (EDX), Atomic Force Microscopy (AFM), X-Ray photoelectron spectroscopy (XPS) techniques allied to quantum chemical studies. Electrochemical results substantiate that the inhibition efficacy of quercetin increases proportionally with the concentration of the inhibitor. The effect of temperature on the corrosion behavior of the alloy was studied in the range of 30–60 °C. Potentiodynamic polarization study confirms the mixed type of inhibition by quercetin with preferential control of the cathodic reaction. The adsorption of quercetin on alloy surface was explained through the Langmuir adsorption isotherm model. ΔG°ads values and its variation with the temperature ensured spontaneous adsorption through chemisorption and the process was endothermic. Further, quantum chemical parameters calculated from Density Functional Theory (DFT) method for quercetin, proved a perfect correlation between structure and corrosion inhibition efficiency. © 2021 Informa UK Limited, trading as Taylor & Francis Group.Item Anti-corrosion investigation of a new nitro veratraldehyde substituted imidazopyridine derivative Schiff base on mild steel surface in hydrochloric acid medium: Experimental, computational, surface morphological analysis(Elsevier Ltd, 2022) Shenoy K, V.; Venugopal, P.P.; Reena Kumari, P.D.; Chakraborty, D.Intensive research has recently been directed toward synthesizing novel, non-toxic, and cost-effective organic inhibitors against metallic corrosion. In the present investigation, a non-toxic, novel Schiff base inhibitor, 6-bromo-(4,5-dimethoxy-2-nitrophenyl) methylidene] imidazo[1,2-a] pyridine-2-carbohydrazide (NVAIP) was synthesized and tested for its corrosion inhibition performance on Mild Steel (MS) in 1 M HCl at 303–323 K using potentiodynamic polarization study, electrochemical impedance spectroscopy (EIS) measurements, Scanning Electron Microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX), Atomic Force Microscopy (AFM) and X-Ray Photoelectron Spectroscopy (XPS) analyses. The electrochemical results stated the inhibition effectiveness (ƞ%) of NVAIP was dependent on concentration and temperature, with the maximum efficiency (92.3%) recorded at 303 K for 500 ppm. The mixed-type inhibitory effect of NVAIP was substantiated by the polarization test results. The Langmuir adsorption isotherm model accorded with the metal surface evaluated, and Gibbs free energy of adsorption values ranged from - 35.05 to-36.05 kJ/mol, implying a physical and chemical adsorption mechanism. Surface morphological analysis was carried out to characterize the chemical composition of the adsorbed inhibitor on the MS surface, and these techniques confirmed that the inhibitive layer is composed of an iron oxide/hydroxide mixture where NVAIP molecules are incorporated. Further, the physicochemical and electronic properties of the NVAIP were investigated using Density Functional Theory (DFT) and electrostatic potential energy mapping (ESP). ΔEads value of −57.21 kcal/mol obtained from Molecular Dynamic (MD) simulations correlates well with the experimental results. Moreover, the relevance of the molecular structure of NVAIP and its inhibition act was validated by quantum chemical calculations and molecular dynamic (MD) simulation studies. A possible inhibition mechanism was proposed based on the experimental, theoretical, and surface analysis results. The outcomes of all the techniques show consistent agreement with each other. © 2022 Elsevier B.V.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 Large and Uniform Single Crystals of MoS2Monolayers for ppb-Level NO2Sensing(American Chemical Society, 2022) Patel, C.; Singh, R.; Dubey, M.; Pandey, S.K.; Upadhyay, S.N.; Kumar, V.; Sriram, S.; Than Htay, M.; Pakhira, S.; Atuchin, V.V.; Mukherjee, S.Recently, unprecedented interest has been immersed toward the synthesis of two-dimensional (2D) transition metal dichalcogenides via the chemical vapor deposition (CVD) system. Synthesis of a uniform and large-sized monolayer MoS2atomic thin film via CVD is still a major bottleneck owing to strong dependence on diverse associated growth parameters. In this work, we have proposed the most viable recipe which is suitable for controlling the nucleation density of Mo and producing a 90 μm-long MoS2monolayer crystal and (695 × 394.8) μm2large MoS2monolayered film on SiO2/Si and c-plane sapphire, respectively. Moreover, MoS2monolayer sensing performance has been thoroughly investigated for NO2exposure at room temperature with a varying response of 4-57.5 for the 100-100 ppm level. Furthermore, the MoS2monolayer sensor exhibits an ultrasensitive NO2detection with limit of detection and limit of qualification values of 1.4 and 4.6 ppb, respectively. In addition, the first-principles-based density functional theory has been employed to analyze the adsorption of NO2on the surfaces of the 2D MoS2monolayer. It is observed that the electronic band gap of the MoS2monolayer after NO2adsorption is reduced by 0.7 eV due to molecular orbital hybridization. © 2022 American Chemical Society. All rights reserved.Item Spin-Transport through Van der Waals Heterojunctions Based on 2D-Ferromagnet and Transition Metal Dichalcogenides: A Study from First-Principles Calculations(John Wiley and Sons Inc, 2022) Devaraj, N.; Tarafder, K.Recently reported 2D ferromagnets show tremendous potential for their application in low-dimensional spintronic devices. Semiconductor heterostructure consisting of 2D ferromagnet integrated with other suitable 2D semiconducting materials may pave the way for designing robust and sophisticated spin-transport devices within a few nanometer scales. In this regard, a detailed understanding of the interface properties of 2D ferromagnetic materials and other 2D semiconductors is highly essential. Herein, the interface properties in the heterostructure made-up of CrX3 (X = Cl, Br, and I) monolayer and transition-metal dichalcogenides (TMDC; MoS2, MoSe2, and WS2) monolayer, using first-principle calculations are systematically studied. This study predicts that a robust spin-dependent barrier originated at the CrX3/TMDC interface. It can lead to a significantly large spin-filtering at the interface while spin-transport through this heterojunction, which will be highly beneficial for spintronic devices applications. Further, detailed spin-dependent transport studies carried out through Co/CrI3/TMDC/CrI3/Co magnetic heterojunctions and substantial tunnel magnetoresistance up to 590%, estimated for these systems. © 2022 Wiley-VCH GmbH.Item Push-Pull Phenoxazine-Based Sensitizers for p-Type DSSCs: Effect of Acceptor Units on Photovoltaic Performance(John Wiley and Sons Inc, 2022) Keremane, K.S.; Planchat, A.; Pellegrin, Y.; Jacquemin, D.; Odobel, F.; Vasudeva Adhikari, A.Finding new efficient p-type sensitizers for NiO photocathodes is a great challenge for the development of promising low-cost tandem dye-sensitized solar cells (DSSCs). Now, the focus of researchers investigating these cells has been to create high-performance p-type systems. With this intention, herein, the design and synthesis of six new phenoxazine-based donor–acceptor (D–A)-configured organic dyes PO1–6 was reported, comprising different acceptor moieties specially designed for the sensitization of mesoporous p-type semiconductor NiO for the construction of p-type DSSCs (p-DSSCs). This work includes structural, photophysical, thermal, electrochemical, theoretical, and photoelectrochemical studies of these dyes, including evaluation of their structure-property relationships. The optical studies revealed that PO1–6 displayed adequate absorption and emission features in the range of 480–550 and 560–650 nm, respectively, with a bandgap in the order of 2.05–2.40 eV, and their thermodynamic parameters favored an efficient interfacial charge transfer involving NiO. Among the six new dyes, the device based on sensitizer PO2 carrying electron-withdrawing 1,3-diethyl-2-thiobarbituric acid achieved the highest power conversion efficiency of 0.031 % (short-circuit current density=0.89 mA cm−2, open-circuit voltage=101 mV, and fill factor=35 %). Conclusively, the study furnishes an understanding of the intricacies involved in the structural modification of phenoxazine-based sensitizers to further ameliorate the performance of the p-type DSSCs. © 2022 Wiley-VCH GmbH.
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