Department Of Physics
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Item Recent advances in 2D anode materials for Na-ion batteries from a theoretical perspective(Taylor and Francis Ltd., 2023-11-02T00:00:00) Verma, Nidhi; Jamdagni, Pooja; Kumar, Ashok; Srivastava, Sunita; Tankeshwar, K.Na-ion batteries (SIBs) are a promising replacement for lithium-ion batteries (LIBs) for low-cost and large-scale energy storage systems in the forthcoming years after additional in-depth examination and investigation. A significant part of the development of innovative anode materials and their in-depth understanding has come through simulations. Ab initio simulations based on density functional theory (DFT) have been proven to be a reliable, efficient, and cost-effective way to design new anode materials for SIBs. As a result of the identification of graphene, researchers and scientists were influenced to create new two-dimensional (2D) materials. On account of their distinctive physical and chemical properties, the broad expanse of surface, innovative electronic features, and charging ability of 2D materials attract much attention. Many of these characteristics are significant prerequisites for using anodes in batteries. Herein, based on recent research progress, we have reviewed the structures and electrochemical properties of 2D materials as anode for Na-ion batteries from a theoretical perspective. The effective methodologies for high-performance anode materials are provided based on the substantial literature and theoretical studies. Added to that, we have also explored the various techniques such as heterostructure, doping, defect- and strain-engineering of 2D materials for the improvement of the performance of these materials as anodes for SIBs. � 2023 Taylor & Francis Group, LLC.Item Role of sintering temperature in tailoring the electrical properties of 0.98KNNS�0.02BNZSH piezoelectric ceramics(Springer, 2023-02-16T00:00:00) Kumar, Amit; Kumari, Sapna; Kumar, V.; Kumar, Ashok; Goyal, P.K.; Aggarwal, Sanjeev; Arya, Anil; Sharma, A.L.Lead-free 0.98(K0.5Na0.5)(Nb0.96Sb0.04O3)�0.02(Bi0.5Na0.5)(Zr0.8Sn0.1Hf0.1)O3 (0.98KNNS�0.02BNZSH) perovskite ferroelectric ceramics have been designed and prepared through the traditional ceramic fabrication technique. To have an insight on the effects of sintering temperature (in the range from 1020 to 1110��C), the structural, microstructural, dielectric and ferro/piezoelectric properties of 0.98KNNS�0.02BNZSH ceramics are investigated systematically. The structural analysis has revealed a pure perovskite phase for sintering at different temperatures. The rhombohedral (R) and orthorhombic (O) phases coexist for sintering of 0.98KNNS�0.02BNZSH ceramic at 1080��C, while the rhombohedral phase dominates above 1080��C. The grains become more uniform and tightly packed when the sintering temperature is increased from 1020 to 1080��C. However, the grain size and the density have been revealed to be decreased for samples sintered above 1080��C. The conduction behavior of 0.98KNNS�0.02BNZSH ceramics has also been investigated using complex impedance spectroscopy. The optimum values of different dielectric and ferro/piezoelectric parameters for 0.98KNNS�0.02BNZSH ceramics sintered at 1080��C are obtained to be as the following: TC ~ 317��C, ?max ~ 7102, tan? ~ 0.10, ? ~ 4.49�g/cm3, d33 ~ 180 pC/N, and Pr ~ 16.7 �C/cm2. These findings show that crystallizability, density, and electrical properties are significantly influenced by the sintering temperature. � 2023, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.Item Janus ?-PdXY (X/Y = S, Se, Te) materials with high anisotropic thermoelectric performance(Royal Society of Chemistry, 2023-02-21T00:00:00) Jakhar, Mukesh; Sharma, Raman; Kumar, AshokTwo-dimensional (2D) materials have garnered considerable attention as emerging thermoelectric (TE) materials owing to their unique density of states (DOS) near the Fermi level. We investigate the TE performance of Janus ?-PdXY (X/Y = S, Se, Te) monolayer materials as a function of carrier concentration and temperature in the mid-range from 300 to 800 K by combining density functional theory (DFT) and semi-classical Boltzmann transport theory. The phonon dispersion spectra and AIMD simulations confirm their thermal and dynamic stability. The transport calculation results reveal the highly anisotropic TE performance of both n and p-type Janus ?-PdXY monolayers. Meanwhile, the coexistence of low phonon group velocity and a converged scattering rate leads to a lower lattice thermal conductivity (Kl) of 0.80 W mK?1, 0.94 W mK?1, and 0.77 W mK?1 along the y-direction for these Janus materials, while the high TE power factor is attributed to the high Seebeck coefficient (S) and electrical conductivity, which are due to the degenerate top valence bands of these Janus monolayers. The combination of lower Kl and a high-power factor at 300 K (800 K) leads to an optimal figure of merit (ZT) of 0.68 (2.21), 0.86 (4.09) and 0.68 (3.63) for p-type Janus PdSSe, PdSeTe and PdSTe monolayers, respectively. To evaluate rational electron transport properties, the effects of acoustic phonon scattering (?ac), impurity scattering (?imp), and polarized phonon scattering (?polar) are included in the temperature-dependent electron relaxation time. These findings indicated that the Janus ?-PdXY monolayers are promising candidates for TE conversion devices. � 2023 The Royal Society of Chemistry.Item First principles study of 2D ring-Te and its electrical contact with a topological Dirac semimetal(Royal Society of Chemistry, 2023-02-10T00:00:00) Singh, Jaspreet; Kumar, AshokIn recent years, researchers have manifested their interest in two-dimensional (2D) mono-elemental materials of group-VI elements because of their excellent optoelectronic, photovoltaic and thermoelectric properties. Despite the intensive recent research efforts, there is still a possibility of novel 2D allotropes of these elements due to their multivalency nature. Here, we have predicted a novel 2D allotrope of tellurium (ring-Te) using density functional theory. Its stability is confirmed by phonon and ab initio molecular dynamics simulations. Ring-Te has an indirect band gap of 0.69 eV (1.16 eV) at the PBE (HSE06) level of theories and undergoes an indirect-direct band gap transition under tensile strain. The higher carrier mobility of holes (?103 cm2 V?1 s?1), good UV-visible light absorption ability and low exciton binding (?0.35 eV) of ring-Te give rise to its potential applications in optoelectronic devices. Furthermore, the electrical contact of ring-Te with a topological Dirac semimetal (sq-Te) under the influence of an electric field shows that the Schottky barriers and contact types can undergo transition from p-type to n-type Schottky contact and then to ohmic contact at a higher electric field. Our study provides an insight into the physics of designing high-performance electrical coupled devices composed of 2D semiconductors and topological semimetals. � 2023 The Royal Society of Chemistry.Item Janus ?-Te2X (X = S, Se) monolayers for efficient excitonic solar cells and photocatalytic water splitting(Royal Society of Chemistry, 2023-01-04T00:00:00) Singh, Jaspreet; Kumar, AshokHighly efficient, environmentally friendly and renewable sources of energy are of great need today to combat increasing energy demands and environmental pollution. In this work, we have investigated the novel 2D allotropes, i.e., ?-Te2X (X = S, Se), using first-principles calculations and study their potential applications in light harvesting devices. Both the monolayers possess high stability and semiconducting nature with an indirect band gap. The high carrier mobilities and excellent optical absorption of these monolayers make them potential candidates for solar conversion applications. We have proposed the type-II heterojunction solar cells and calculated their power conversion efficiencies (PCEs). The small conduction band offset and appropriate band gap of donor material in the case of ?-Te2S(S-Side)/?-Te2S(Te-Side) heterojunction results in a PCE of ?21%. In addition, the band alignments of these monolayers properly engulf the redox potentials of water. The overpotentials required to trigger hydrogen reduction (HER) and water oxidation (OER) half reactions reveal that HER and OER preferred acidic and neutral media, respectively. The calculated solar-to-hydrogen (STH) efficiencies of ?-Te2S (?-Te2Se) monolayers turn out to be ?13% (?12%), respectively, which implies their practical applications in water splitting. Thus, our work provides strong evidence regarding the potential applications of these materials in the field of light harvesting devices. � 2023 The Royal Society of Chemistry.Item Photocatalytic properties of anisotropic ?-PtX2 (X = S, Se) and Janus ?-PtSSe monolayers(Royal Society of Chemistry, 2022-09-01T00:00:00) Jamdagni, Pooja; Kumar, Ashok; Srivastava, Sunita; Pandey, Ravindra; Tankeshwar, K.The highly efficient photocatalytic water splitting process to produce clean energy requires novel semiconductor materials to achieve a high solar-to-hydrogen energy conversion efficiency. Herein, the photocatalytic properties of anisotropic ?-PtX2 (X = S, Se) and Janus ?-PtSSe monolayers were investigated based on the density functional theory. The small cleavage energy for ?-PtS2 (0.44 J m?2) and ?-PtSe2 (0.40 J m?2) endorses the possibility of mechanical exfoliation from their respective layered bulk materials. The calculated results revealed that the ?-PtX2 monolayers have an appropriate bandgap (?1.8-2.6 eV) enclosing the water redox potential, light absorption coefficient (?104 cm?1), and exciton binding energy (?0.5-0.7 eV), which facilitates excellent visible-light-driven photocatalytic performance. Remarkably, the inherent structural anisotropy leads to an anisotropic high carrier mobility (up to ?5 � 103 cm2 V?1 S?1), leading to a fast transport of photogenerated carriers. Notably, the required small external potential to realize hydrogen evolution reaction and oxygen evolution reaction processes with an excellent solar-to-hydrogen energy conversion efficiency for ?-PtSe2 (?16%) and ?-PtSSe (?18%) makes them promising candidates for solar water splitting applications. � 2022 The Royal Society of Chemistry.Item Optoelectronic and photocatalytic properties of stable pentagonal B2S and B2Se monolayers(Elsevier B.V., 2022-06-01T00:00:00) Katoch, Neha; Kumar, Jagdish; Kumar, Ashok; Ahluwalia, P.K.; Pandey, RavindraBoron-based 2D monolayers have attracted tremendous interest due to their unique physical and chemical properties. In this paper, we report novel pentagonal monolayers, B2S and B2Se, which are predicted to be energetically, dynamically, and thermally stable based on density functional theory. At the HSE06 level of theory, they exhibit a moderate indirect bandgap of (e.g., 1.82 eV for Penta-B2S and 1.94 eV for Penta-B2Se). Strain-induced indirect-to-direct bandgap transition, high hole mobility (~103 Cm2V-1S-1) and strong optical absorption (? ~105 Cm-1) in the visible region are observed for these monolayers. Moreover, the electronic band structures and optical spectra are tunable by mechanical strains suggesting their visible light-harvesting capabilities for optoelectronic applications. In this way, the pentagonal family of 2D materials is now expanded to include boron-containing photocatalytic materials for water splitting applications. � 2022Item Mechanical, optical and thermoelectric properties of Janus BiTeCl monolayer(Elsevier Ltd, 2022-04-29T00:00:00) Chauhan, Poonam; Singh, Jaspreet; Kumar, AshokWe report mechanical, optical and thermoelectric properties of recently fabricated Janus BiTeCl monolayer using density functional and semi-classical Boltzmann transport theory. Janus BiTeCl monolayer exhibits a direct bandgap, high carrier mobility (?103 cm2V?1s?1) and high optical absorption in the UV�visible region. The mechanical behavior of the Janus BiTeCl monolayer is nearly isotropic having an ideal tensile strength ?15 GPa. The higher value of the Gruneisen parameter (?), a low value of phonon group velocity (vg), and very little phonon scattering time (?p) lead to low lattice thermal conductivity (1.46 W/mK) of Janus BiTeCl monolayer. The combined effect of thermal conductivity and electronic transport coefficients of Janus BiTeCl monolayer results in the figure of merit (ZT) in the range of 0.43�0.75 at 300�500 K. Our results suggest Janus BiTeCl monolayer be a potential candidate for optoelectronic and moderate temperature thermoelectric applications. � 2022Item Engineering 2D Materials for Photocatalytic Water-Splitting from a Theoretical Perspective(MDPI, 2022-03-21T00:00:00) Jakhar, Mukesh; Kumar, Ashok; Ahluwalia, Pradeep K.; Tankeshwar, Kumar; Pandey, RavindraSplitting of water with the help of photocatalysts has gained a strong interest in the scientific community for producing clean energy, thus requiring novel semiconductor materials to achieve highyield hydrogen production. The emergence of 2D nanoscale materials with remarkable electronic and optical properties has received much attention in this field. Owing to the recent developments in highend computation and advanced electronic structure theories, first principles studies offer powerful tools to screen photocatalytic systems reliably and efficiently. This review is organized to highlight the essential properties of 2D photocatalysts and the recent advances in the theoretical engineering of 2D materials for the improvement in photocatalytic overall water-splitting. The advancement in the strategies including (i) single-atom catalysts, (ii) defect engineering, (iii) strain engineering, (iv) Janus structures, (v) type-II heterostructures (vi) Z-scheme heterostructures (vii) multilayer configurations (viii) edge-modification in nanoribbons and (ix) the effect of pH in overall watersplitting are summarized to improve the existing problems for a photocatalytic catalytic reaction such as overcoming large overpotential to trigger the water-splitting reactions without using cocatalysts. This review could serve as a bridge between theoretical and experimental research on next-generation 2D photocatalysts. � 2022 by the authors. Licensee MDPI, Basel, Switzerland.Item Stability, optoelectronic and thermal properties of two-dimensional Janus ?-Te2S(IOP Publishing Ltd, 2022-02-14T00:00:00) Singh, Jaspreet; Jakhar, Mukesh; Kumar, AshokMotivated by recent progress in the two-dimensional (2D) materials of group VI elements and their experimental fabrication, we have investigated the stability, optoelectronic and thermal properties of Janus ?-Te2S monolayer using first-principles calculations. The phonon dispersion and MD simulations confirm its dynamical and thermal stability. The moderate band gap ( 1/41.5 eV), ultrahigh carrier mobility ( 1/4103 cm2 V-1 s-1), small exciton binding energy (0.26 eV), broad optical absorption range and charge carrier separation ability due to potential difference ( "V = 1.07 eV) on two surfaces of Janus ?-Te2S monolayer makes it a promising candidate for solar energy conversion. We propose various type-II heterostructures consisting of Janus ?-Te2S and other transition metal dichalcogenides for solar cell applications. The calculated power conversion efficiencies of the proposed heterostructures, i.e. ?-Te2S/T-PdS2, ?-Te2S/BP and ?-Te2S/H-MoS2 are 1/421%, 1/419% and 18%, respectively. Also, the ultralow value of lattice thermal conductivity (1.16 W m-1 K-1) of Janus ?-Te2S makes it a promising material for the fabrication of next-generation thermal energy conversion devices. � 2022 IOP Publishing Ltd.