Faculty Publications

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Mechanical Instabilities in 2D-SiC with Defects
(American Institute of Physics Inc., 2023) Madhusoodanan, M.; Narayanan, M.K.; Madam, A.K.
Elasticity of material is important in understanding the elastic deformation, to flexure, to strain softening. Elastic properties provide the measure of resistance of a system to elastic deformation thus validating its structural stability. Understanding the elasticity of a material is important in understanding their response to any external perturbations. This is required for their synthesis and practical applications. Mechanical stability is determined through the knowledge of second order elastic constants (SOEC) and the higher order elastic constants are necessary to understand the non-linear, anharmonic behaviors. A material is said to be mechanically stable satisfying the Born stability criteria. Here, 2D-SiC, a silicene derivative is introduced with point and topological defects to understand its variation in mechanical properties. Defects namely, mono-, bi- and Stone-Wales types are incorporated into SiC. Computed values of elastic constants implied mechanical instability for C removed monovacancy. All other configurations implied mechanical stability satisfying Born criteria. Â© 2023 American Institute of Physics Inc.. All rights reserved.
Semiconducting B13C2 system: Structure search and DFT-based analysis
(Institute of Physics, 2019) Pillai, H.G.; Madam, A.K.; Chandra, S.; Cheruvalath, V.M.
DFT calculation on Boron Carbide in B13C2 stoichiometry using a 15-atom unit cell necessarily results in metallic ground state regardless of the crystal structure. This is because such a unit cell consists of odd number of electrons, and hence complete filling of the top most band(s) of nonzero occupancy is impossible. This is in contrast to the observed semiconducting nature. If the crystal structure of B13C2 is made of a 30-atom unit cell which cannot be reduced to a 15 atom cell, there is a possibility of obtaining either a metallic or a semiconducting state as such a cell consists of an even number of electrons. In this work the evolutionary algorithm based structure search using 30-atom unit cells has yielded a previously unreported semiconducting system of B13C2 with unique bonding pattern. The mechanical and dynamical stability of the system have been properly established through the computation of elastic constants and phonon spectra. Its bond lengths, elastic moduli, hardness and infrared spectrum are in good agreement with experimental data. ©2019 IOP Publishing Ltd.
Stone-Wales Defect Induced Performance Improvement of BC3 Monolayer for High Capacity Lithium-Ion Rechargeable Battery Anode Applications
(American Chemical Society, 2020) Thomas, S.; Madam, A.K.; Asle Zaeem, M.A.
First-principles density functional theory (DFT) computations were adopted to assess the potential application of a boron carbide (BC3) monolayer with point and topological defects as an anode material in alkali metal-based lithium (Li) ion rechargeable batteries. Results show that point defects (mono and bi vacancies) induce a large structural deformation upon Li intercalation which restricts their use for anode application. However, the Stone-Wales defect filled BC3 monolayer shows high structural stability with a negative Li binding energy of -1.961 eV in comparison with -0.930 eV of its pristine form. It is also noticed that after adsorbing the Li atom, the semiconducting characteristics of both the pristine and Stone-Wales defect filled BC3 monolayers are transformed into metallic, electrically conductive states. More importantly, the Li alkali metal atom shows fast diffusion on the surfaces of both the pristine and the Stone-Wales defect filled BC3 monolayers with low energy barriers of 0.34 and 0.33 eV, respectively. Besides, both the pristine and Stone-Wales defect filled BC3 monolayers exhibit high theoretical specific capacities of 1144 and 1287 mAhg-1, which are much higher than that of a traditional graphite anode and stand among the highest values of anode materials detailed in literature. The Li alkali metal intercalated monolayers BC3 show small average open-circuit voltages of 0.485 and 0.465 V for pristine and Stone-Wales defect cases, respectively. On the basis of the aforementioned details, the present study suggests that the Stone-Wales type topological defect incorporated BC3 monolayer is a promising anode material for Li-ion based rechargeable batteries with high storage capacity, low Li diffusion energy barrier, and low average open-circuit voltage. © 2020 American Chemical Society.
From fundamental to CO2 and COCl2 gas sensing properties of pristine and defective Si2BN monolayers
(Royal Society of Chemistry, 2022) Thomas, S.; Madam, A.K.; Asle Zaeem, M.
In this work, the capability of Si2BN monolayers (Si2BN-MLs) to sense CO2 and COCl2 molecules was investigated by analyzing the structural, electronic, mechanical and gas sensing properties of defect-free and defective Si2BN-ML structures. Electronic property analysis revealed that the Si2BN-ML retains its metallicity in the presence of vacancy defects. The computed vacancy formation energies of Si, B and N monovacancies are 3.25 eV, 2.27 eV and 2.55 eV, respectively, which indicate that the B monovacancy is thermodynamically more feasible. Besides, both pristine and defective Si2BN-ML structures show good mechanical stability. To validate the gas sensing properties, the adsorption energy and charge transfer were analysed, showing that both pristine and defective Si2BN-ML structures receive considerable charges from the CO2 and COCl2 molecules via a stable physisorption process. The work function analysis revealed that a minute increase <0.10 eV is responsible for the enhanced selectivity and sensitivity of Si2BN-ML structures in detecting CO2 and COCl2 molecules. The low adsorption energies of both CO2 and COCl2 gas molecules during the interaction with Si2BN-ML structures signify the possibility of a large number of adsorption-desorption cycles with an ultra-low recovery time, 0.174 ns for CO2 and 0.016 ns for COCl2, suitable for efficient gas sensing applications. © the Owner Societies.

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