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Singh Y. T.,Patra P. K.,Obodo K. O.,Rai D. P. 한국탄소학회 2022 Carbon Letters Vol.32 No.2
We investigated the electronic and mechanical properties of single-walled carbon nanotubes (SWCNTs) with different tube diameters using density functional theory (DFT) and molecular dynamics (MD) simulation, respectively. The carbon nanotubes’ electronic properties were derived from the index number (n1 , n2 ), lattice vectors, and the rolled graphene sheet orientation. For (6,1) SWCNT, (n1 -n2 )/3 is non-integer, so the expected characteristic is semiconducting. We have considered (6,1) Chiral SWCNT with different diameters ‘d’ (4.68 Å, 4.90 Å, 5.14 Å, 5.32 Å, 5.53 Å) corresponds to respective bond lengths ‘δ ’ (1.32 Å, 1.38 Å, 1.45 Å, 1.50 Å and 1.56 Å) and then analyze the electronic properties from the Linear Combination of Atomic Orbitals (LCAO) based on DFT. We have used both the DFT-1/2 and GGA exchange energy correlation approximations for our calculation and compared the results. In both cases, the energy bandgap is decreasing order with the increase in bond lengths. The lowest value of formation energy was obtained at the bond length δ=1.45 Å (d=5.14 Å). For the mechanical properties, we have calculated Young’s modulus using molecular dynamics (MD) simulations. From our calculation, we have found that the (6,1) SWCNT with bond length 1.45 Å (d=5.14 Å) has Young’s modulus value of 1.553 TPa.
Singh, L.,Yadava, S. S.,Sin, B. C.,Rai, U. S.,Mandal, K. D.,Lee, Y. Springer Science + Business Media 2016 Journal of electronic materials Vol.45 No.6
<P>The dielectric and ferroelectric characteristics of Bi0.5Na0.5TiO3 (BNT), CaCu3Ti4O12 (CCTO), and 0.5Bi(0.5)Na(0.5)TiO(3)-0.5CaCu(3)Ti(4)O(12) (BNT/CCTO) ceramics are compared. X-ray diffraction patterns confirmed the formation of single phase of all the ceramics after sintering at 950A degrees C for 15 h. Scanning electron microscopy images of the sintered ceramics reveal average grain sizes in the range from 200 nm to 2.5 mu m. Energy-dispersive x-ray mapping and x-ray photoelectron spectroscopy show the presence of the elements Bi, Na, Ca, Cu, Ti, and O with uniform distribution in the ceramics. BNT/CCTO exhibits high dielectric constant (epsilon (r) similar to 6.9 x 10(4)) compared with BNT (epsilon (r) similar to 0.13 x 10(4)) and CCTO (epsilon (r) similar to 1.68 x 10(4)) ceramics at 1 kHz and 503 K. The high dielectric constant of BNT/CCTO compared with BNT and CCTO is associated with a major contribution from grain boundaries, as confirmed by impedance and modulus analyses. The P-E hysteresis loop of all the ceramics measured at room temperature and 50A degrees C exhibited typical ferroelectric nature. The remanent polarization (P (r)) of BNT (1.58 mu C/cm(2)) and CCTO (0.654 mu C/cm(2)) ceramics are higher than that of BNT/CCTO (0.267 mu C/cm(2)) ceramic.</P>
Highly Efficient Photocatalytic Studies on Bi36 Fe2 O57 Ceramic Synthesized by Chemical Route
Manish Kumar Verma,Vinod Kumar,Upakar Patel,Vishnu Shankar Rai,Anup Kumar,Arup Kumar De,Aditya Kumar Prajapati,Dinesh Prajapati,Kedar Sahoo,Tapas Das,N. B. Singh,K. D. Mandal 한국전기전자재료학회 2023 Transactions on Electrical and Electronic Material Vol.24 No.5
Bi36 Fe2 O57 (BFO) polycrystalline ceramic was synthesized by economical chemical route. The single-phase formation of BFO ceramic was confirmed by powder X-ray diffraction studies. Nanosized formation of BFO ceramics established by XRD and TEM analysis. The bimodal distribution of grain size is observed with size ranging from 50 to 600 nm. It observed that the Bi36 Fe2 O57 photocatalyst exhibited higher catalytic activity for the degradation of Methylene Blue (MB) under visible-light irradiation The oxidation state of elements present in the BFO ceramic, was confirmed by XPS studies. The pseudocapacitive nature of BFO ceramic was observed by cyclic Voltammetry. The dielectric constant of BFO ceramic was found 375 at 1 kHz at 300 K. The dielectric loss was found 0.51 at 100 kHz and 300 K.
An Abinitio Study of the Half-metallic Properties of Co2TGe (T=Sc, Ti, V,Cr, Mn, Fe): LSDA+U Method
D. P. Rai,R. K. Thapa 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.11
Using density functional theory (DFT) calculations, we investigated the electronic and magnetic properties of the Heusler compounds Co2TGe (T = Sc, Ti, V, Cr, Mn, Fe). Among the systems under investigation Co2CrGe and Co2MnGe have given 100% spin polarization at the Fermi energy (EF ). Co2CrGe is the most stable half-metallic ferromagnets (HMFs) with an energy gap of 0.24 eV at the Fermi level (EF ) in spin down channel. We have also found an increase in the total magnetic moments as T goes from Sc to Fe. The calculated magnetic moments for Co2CrGe and Co2MnGe are 3.999 µB and 5.00 µB respectively. Based on the local spin density approximation (LSDA)calculated results, we have predicted that the compounds Co2CrGe and Co2MnGe are HMFs. We have tried to study the HMFs in Co2ScGe, Co2TiGe, Co2VGe and Co2FeGe by using the local spin density approximation and Coulomb repulsion (U) (LSDA+U) when the simple generalized gradient approximation (GGA) or the LSDA fail.
Synchronization and Operation of Parallel Inverters using Droop Control
L. K. Sahoo,N. D. Thakur,K. Rai,P Sensarma,R. D. Jha,P. Mohanty,A Sharma 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5
To obtain a continuous power supply Distributed Generation (DG) with a Decentralized Power System (DPS), i.e. replacing a single UPS unit with multiple, smaller units in parallel, is emerging as new paradigm. The technically challenging aspect of DPS is the synchronization of inverters and load sharing among the parallel connected inverters. In this paper, a control method is proposed and implemented for synchronization and parallel operation of inverters. Droop control method has been used for equal power sharing, and design of power control loop. The design issues for voltage control loop are analyzed with the discussion of relative stability of the system. A current control loop is designed and analyzed to provide synchronization between the inverters.
D. P. Rai,Y. T. Singh,B. Chettri,M. Houmad,P. K. Patra 한국탄소학회 2021 Carbon Letters Vol.31 No.3
We report the comparative study of electronic and optical properties of (6,1) SWCNT from GGA and DFT-1/2 methods. (6,1) SWCNT is a low-bandgap semiconductor, which falls within ( n1 ? n2)/3≠ integer. The calculated bandgaps are 0.371 eV and 0.462 eV from GGA and DFT-1/2, respectively. Thus, DFT-1/2 enhanced the electronic bandgap by 24.52%. From both GGA and DFT-1/2 approaches (6,1) SWCNT exhibits an indirect bandgap along Γ ? Δ symmetry. However, the percentage change in direct–indirect bandgap is negligibly small, i.e., 4.1% and 3.7% from GGA and DFT-1/2, respectively. The refractive index measured along x-axis ( n x ) approaches unity, indicating transparent behaviour, while that along z-axis ( n z ) goes as high as ∼3.82 for photon energy 0.0 ? 0.15 eV, exhibiting opaque behaviour. Again, the value of n z drops below unity at photon energy ∼0.18 eV and again approaches ∼ 1 for higher energy ranges. The optical absorption is highly anisotropic and active within the infrared region.
SILICON QUANTUM DOTS GROWTH IN SiNx DIELECTRIC: A REVIEW
A. K. PANCHAL,D. K. RAI,M. MATHEW,C. S. SOLANKI 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2009 NANO Vol.4 No.5
This paper reviews research works carried out on silicon quantum dots (Si-QDs) embedded in the silicon nitride (SiNx) dielectric matrix films with different fabrication techniques and different characteristics. The advantages of SiNx as a dielectric compared to silicon dioxide (SiO2) for Si-QDs from a device point of view are discussed. Various fabrication techniques along with different optimized deposition conditions are summarized. The typical results of structural characteristics of the films with Raman spectroscopy and Transmission Electron Microscopy (TEM) are discussed. The origin of photoluminescence (PL) from the films and the chemical compositional analysis such as X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Secondary Ion Mass Spectroscopy (SIMS) analysis of the films are also made available in brief. The charge conduction mechanism in the films with metal–insulator–semiconductor (MIS) structure, with their electrical characterization like capacitance–voltage (C–V) and current–voltage (I–V) measurements are presented.
Dinesh Prajapati,Vishnu Shankar Rai,Vinod Kumar,Manish Kumar Verma,Atendra Kumar,N. B. Singh,K. D. Mandal 한국전기전자재료학회 2023 Transactions on Electrical and Electronic Material Vol.24 No.3
An Aurivillius oxide, Bi(2/3)-xGdxCu3Ti4O12 (x = 0.05, 0.10, and 0.20) ceramic designated as BGCTO-0.05, BGCTO-0.1 and BGCTO-0.2 has been fabricated by modified solid-state route resemble with semi wet route and characterized by using various techniques including XRD, SEM, EDX, TEM and XPS for getting information about phase formation, morphology, particle size distribution and oxidation state of elements of synthesized ceramics. X-ray diffraction pattern confirmed the single-phase formation of BGCTO ceramic. The crystalline nature of BGCTO ceramic for few selected compositions, x = 0.05, 0.10, and 0.20 were observed by TEM analysis. Further, particle size was determined with the help of Image J software and found to be 90.85 ± 5 nm, 75.35 ± 5 nm and 72.43 ± 5 nm, respectively for BGCTO-0.05, BGCTO-0.1 and BGCTO-0.2 ceramic. The dielectric permittivity (εr) as well as tangent loss (tan δ) was observed at room temperature and 1 kHz for all synthesized ceramics. The electrical behaviour of BGCTO ceramic revealed the presence of semiconducting grain separated by grain boundaries.