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Ahuja, Rajeev
Publications (10 of 59) Show all publications
Khossossi, N., Banerjee, A., Benhouria, Y., Essaoudi, I., Ainane, A. & Ahuja, R. (2019). Ab initio study of a 2D h-BAs monolayer: a promising anode material for alkali-metal ion batteries. Physical Chemistry, Chemical Physics - PCCP, 21(33), 18328-18337
Open this publication in new window or tab >>Ab initio study of a 2D h-BAs monolayer: a promising anode material for alkali-metal ion batteries
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2019 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, no 33, p. 18328-18337Article in journal (Refereed) Published
Abstract [en]

The selection of a suitable two dimensional anode material is one of the key steps in the development of alkali metal ion batteries to achieve superior performance with an ultrahigh rate of charging/discharging capability. Here, we have used state of the art density functional theory (DFT) to explore the feasibility of two dimensional (2D) honeycomb boron arsenide (h-BAs) as a potential anode for alkali-metal (Li/Na/K)-ion batteries. The structural and dynamic stability has been confirmed from the formation energy and the non-negative phonon frequency. The h-BAs monolayer exhibits negative adsorption-energy values of -0.422, -0.321 and -0.814 eV, for the Li, Na, and K-ions, respectively. Subsequently, during the charging process the adsorption-energy increases considerably without an energy-barrier when any of the A-atoms achieve a crucial distance (similar to 8 angstrom). In addition, it has been observed that insertion of the mono alkali metal atom into the h-BAs surface results in the semi-conducting nature of the monolayer being transformed into a metallic-state. The low energy barriers for Li (0.522 eV), Na (0.248), and K (0.204 eV) active ion migration imply high diffusion over the h-BAs surface, hence suggesting it has a high charge/discharge capability. Moreover, we have obtained low average operating voltages of 0.49 V (Li), 0.35 V (Na) and 0.26 V (K) and high theoretical capacities of 522.08 mA h g(-1) (for Li and Na) and 209.46 mA h g(-1) (for K) in this study. The aforementioned findings indicate that a h-BAs monolayer could be a promising anode material in the search for low cost and high performance alkali metal ion batteries.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2019
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-259418 (URN)10.1039/c9cp03242h (DOI)000482471400031 ()31397457 (PubMedID)2-s2.0-85071496044 (Scopus ID)
Note

QC 20190924

Available from: 2019-09-24 Created: 2019-09-24 Last updated: 2019-09-24Bibliographically approved
Johansson, M. B., Philippe, B., Banerjee, A., Phuyal, D., Mukherjee, S., Chakraborty, S., . . . Johansson, E. M. J. (2019). Cesium Bismuth Iodide Solar Cells from Systematic Molar Ratio Variation of CsI and BiI3. Inorganic Chemistry, 58(18), 12040-12052
Open this publication in new window or tab >>Cesium Bismuth Iodide Solar Cells from Systematic Molar Ratio Variation of CsI and BiI3
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2019 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 58, no 18, p. 12040-12052Article in journal (Refereed) Published
Abstract [en]

Metal halide compounds with photovoltaic properties prepared from solution have received increased attention for utilization in solar cells. In this work, low-toxicity cesium bismuth iodides are synthesized from solution, and their photovoltaic and, optical properties as well as electronic and crystal structures are investigated. The X-ray diffraction patterns reveal that a CsI/BiI3 precursor ratio of 1.5:1 can convert pure rhombohedral BiI3 to pure hexagonal Cs3Bi2I9, but any ratio intermediate of this stoichiometry and pure BiI3 yields a mixture containing the two crystalline phases Cs3Bi2I9 and BiI3, with their relative fraction depending on the CsI/BiI3 ratio. Solar cells from the series of compounds are characterized, showing the highest efficiency for the compounds with a mixture of the two structures. The energies of the valence band edge were estimated using hard and soft X-ray photoelectron spectroscopy for more bulk and surface electronic properties, respectively. On the basis of these measurements, together with UV-vis-near-IR spectrophotometry, measuring the band gap, and Kelvin probe measurements for estimating the work function, an approximate energy diagram has been compiled clarifying the relationship between the positions of the valence and conduction band edges and the Fermi level.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-261309 (URN)10.1021/acs.inorgchem.9b01233 (DOI)000486565600024 ()31483638 (PubMedID)2-s2.0-85072233759 (Scopus ID)
Note

QC 20191008

Available from: 2019-10-08 Created: 2019-10-08 Last updated: 2019-10-16Bibliographically approved
Klaa, K., Labidi, S., Banerjee, A., Chakraborty, S., Labidi, M., Amara, A., . . . Ahuja, R. (2019). Composition dependent tuning of electronic and magnetic properties in transition metal substituted Rock-salt MgO. Journal of Magnetism and Magnetic Materials, 475, 44-53
Open this publication in new window or tab >>Composition dependent tuning of electronic and magnetic properties in transition metal substituted Rock-salt MgO
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2019 (English)In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 475, p. 44-53Article in journal (Refereed) Published
Abstract [en]

Full potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory (DFT) is used to investigate the structural, electronic and magnetic properties of Fe and Ni (3d transition metal) substituted Rock-salt wide band gap insulator Mg1-xMxO (M = Fe, Ni). We have performed spin polarized calculations throughout this work with generalized gradient approximation (GGA) type exchange correlation functional. Additionally, the electronic structures and density of states are computed using modified Becke-Johnson (mBJ) potential based approximation with the inclusion of coulomb energy (U = 7 eV). Based on the Vegard's law and structural optimization, the lattice parameter and bulk modulus are found to be in good agreement with experimental values. Moreover, the analysis of electronic band structures reveals an insulating character for Ni substituted MgO while semiconducting and half-metallic character for Fe substituted case. It has been found that the p-d super-exchange interaction provides a ferromagnetic character due to the 3d transition metal impurities and oxygen atom. The observed p-d hybridization at the top of the valence band edge in this investigations could be useful for magneto-optic and spintronic applications.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2019
Keywords
FP-LAPW, mBJ plus U, P-d exchange interaction, Half-metallic, Magnetic moment
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-245123 (URN)10.1016/j.jmmm.2018.11.065 (DOI)000458152000008 ()2-s2.0-85057479802 (Scopus ID)
Note

QC 20190315

Available from: 2019-03-15 Created: 2019-03-15 Last updated: 2019-03-15Bibliographically approved
Watcharatharapong, T., T-Thienprasert, J., Chakraborty, S. & Ahuja, R. (2019). Defect formations and pH-dependent kinetics in krohnkite Na2Fe (SO4)(2)center dot 2H(2)O based cathode for sodium-ion batteries: Resembling synthesis conditions through chemical potential landscape. Nano Energy, 55, 123-134
Open this publication in new window or tab >>Defect formations and pH-dependent kinetics in krohnkite Na2Fe (SO4)(2)center dot 2H(2)O based cathode for sodium-ion batteries: Resembling synthesis conditions through chemical potential landscape
2019 (English)In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 55, p. 123-134Article in journal (Refereed) Published
Abstract [en]

Thermodynamics and kinetics of intrinsic point defects in Na2Fe(SO4)(2)center dot 2H(2)O, a high-voltage cathode for Na-ion batteries, are studied by means of first-principles density functional theory. Electronic structures of charged defects are calculated to study their influences towards electronic and electrochemical properties as well as to probe hole polaron formation. As defect formation energy strongly depends on atomic chemical potentials, we initiate a systematic approach to determine their valid ranges for the pentrary Na-Fe-S-O-H compound under thermodynamic equilibria and correlate them with approximated pH parameters in solution-based synthesis. Given chemical potential landscape and formation energy, we find that Fe-Na(1+), V-Na(1-,0) and Na-Fe(1-,0) are dominant and their concentrations could be manipulated through pH condition and oxygen content in the precursor solution. It is predicted that the channel blockage due to Fe-Na would appear under strong acidic growth condition but could be diminished under weak acidic condition (4.7 <= pH <= 5.6) where Na-Fe facilitates a faster migration between each diffusion channel. Our results do not only explain the origin of intercalation mechanism and improved electronic conduction, but also demonstrates the pH influence towards conductivities in the cathode material.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2019
Keywords
Chemical potentials, Defects, DFT, Diffusions, Sodium-ion batteries
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-241320 (URN)10.1016/j.nanoen.2018.10.038 (DOI)000454636200012 ()2-s2.0-85056190760 (Scopus ID)
Note

QC 20190125

Available from: 2019-01-25 Created: 2019-01-25 Last updated: 2019-01-25Bibliographically approved
Watcharatharapong, T., Chakraborty, S. & Ahuja, R. (2019). Defect Thermodynamics in Nonstoichiometric Alluaudite-Based Polyanionic Materials for Na-Ion Batteries. ACS Applied Materials and Interfaces, 11(36), 32856-32868
Open this publication in new window or tab >>Defect Thermodynamics in Nonstoichiometric Alluaudite-Based Polyanionic Materials for Na-Ion Batteries
2019 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 11, no 36, p. 32856-32868Article in journal (Refereed) Published
Abstract [en]

Sodium iron sulfate in the form of alluaudite Na2+2xFe2-x(SO4)3 (or NFSx) has emerged as one of the most promising cathodes for Na-ion batteries due to its highest Fe2+/3+ redox potential, low cost, sustainability, and high rate capability. Unlike most of the other cathodes, NFSx generally crystalizes in its nonstoichiometric form with partial Na substitution for Fe sites and contains a small amount of impurities. However, profound explanations behind this inherent behavior including others, like phase stability, configurational structure, and defect formation are still ambiguous. We therefore performed first-principles calculations combined with a random swapping method to determine the minimum energy configurations of NFSx (with x = 0, 0.25, and 0.5) and find a correlation between the Na distribution pattern and energetics in which the site preference for Na+ ion is in a sequence of Na4 &gt; Na1 &gt; Na2 &gt; Na3. Our result points out that the nonstoichiometry cannot be properly described under the framework of primitive structures. Moreover, we investigated phase stability diagrams and defect formations based on thermodynamic criteria. Our predicted phase diagrams can explain the inevitable impurity precipitation, which can be reduced as x diminishes. Defect formation analysis indicates an unlikely formation of channel blockage and identifies the dominant formation of FeNa + VNa and Nai + NaFe complexes. While the former can become spontaneous in a Na-deficient environment, the latter occurs mainly in NFS0 and accommodates the presence of nonstoichiometry. Copyright

Place, publisher, year, edition, pages
American Chemical Society, 2019
Keywords
batteries, chemical potentials, defect formation energies, density functional theory, impurities, minimum energy configurations, nonstoichiometry, phase diagrams, Binary alloys, Calculations, Cathodes, Chemical potential, Defects, Ions, Iron compounds, Phase stability, Redox reactions, Sodium compounds, Solar cells, Stability criteria, Sulfur compounds, Sustainable development, Thermodynamics, Vanadium alloys, Distribution patterns, First-principles calculation, High rate capability, Minimum energy configuration, Non-stoichiometry, Phase stability diagram, Polyanionic materials, Sodium-ion batteries
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-263572 (URN)10.1021/acsami.9b07027 (DOI)000486360500028 ()2-s2.0-85072058881 (Scopus ID)
Note

QC20191106

Available from: 2019-11-06 Created: 2019-11-06 Last updated: 2019-11-06Bibliographically approved
Singh, D. & Ahuja, R. (2019). Enhanced Optoelectronic and Thermoelectric Properties by Intrinsic Structural Defects in Monolayer HfS2. ACS APPLIED ENERGY MATERIALS, 2(9), 6891-6903
Open this publication in new window or tab >>Enhanced Optoelectronic and Thermoelectric Properties by Intrinsic Structural Defects in Monolayer HfS2
2019 (English)In: ACS APPLIED ENERGY MATERIALS, ISSN 2574-0962, Vol. 2, no 9, p. 6891-6903Article in journal (Refereed) Published
Abstract [en]

In the present work, we have studied the electronic, optical, and thermoelectric properties of a monolayer of pristine HfS2 and two types of vacancy and two types of dopant by using first-principles calculations. These configurations with single atom vacancy (Hf and S atoms) and single atom dopant in place of a sulfur atom are energetically more favorable. The electronic properties of HfS2 monolayer are significantly affected by vacancies as well as dopants. Also, it transforms indirect-band-gap semiconducting behavior to direct-band-gap semiconducting behavior and semiconductor-to-metal HfS2 occurs during the structural defect. The variation in the work function of HfS2 monolayer by vacancy, as well as dopant, indicates the change in conductivity. The structural defect enhancing the light absorption as well as the conductivity of HfS2 monolayer and H-phase of it is suitable for UV light absorption while the T-phase is suitable for visible light absorption. From the thermoelectric properties, the relatively high Seebeck coefficient and it is found to be 2867 and 2902 mu V K-1 for doped P atom in the T-phase and the pristine H-phase, respectively, at room temperature. The figure of merit (ZT) at 300 K is determined to be 1 for the T-phase and 1.05 for the H-phase, while, at a higher temperature, ZT = 1.23 for the Hf vacancy in the T-phase. Such analysis reveals that the structural defects not only significantly affect the electronic properties, but they also can be used as an efficient way to modulate the thermoelectric properties and enhance ZT. The theoretical results suggest that the two-dimensional HfS2 monolayer is very useful in high-performance optoelectronic and thermoelectric devices.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2019
Keywords
HfS2 monolayer, vacancy and doping defects, electronic and optical properties, thermoelectric properties, first-principles calculations
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-261976 (URN)10.1021/acsaem.9b01402 (DOI)000487770000087 ()
Note

QC 20191014

Available from: 2019-10-14 Created: 2019-10-14 Last updated: 2019-10-14Bibliographically approved
Das, T., Chakraborty, S., Ahuja, R. & Das, G. P. (2019). Functionalization and Defect-Driven Water Splitting Mechanism on a Quasi-Two-Dimensional TiO2 Hexagonal Nanosheet. ACS Applied Energy Materials, 2(7), 5074-5082
Open this publication in new window or tab >>Functionalization and Defect-Driven Water Splitting Mechanism on a Quasi-Two-Dimensional TiO2 Hexagonal Nanosheet
2019 (English)In: ACS Applied Energy Materials, ISSN 2574-0962, Vol. 2, no 7, p. 5074-5082Article in journal (Refereed) Published
Abstract [en]

In this work, we have dealt with the functionalization of a newly reported quasi-2D hexagonal nanosheet (HNS) of titanium dioxide (TiO2) for photocatalytic water splitting to generate hydrogen and oxygen. Functionalization has been carried out by creating a single oxygen vacancy defect as well as by incorporating substitutional doping with C, N, P, and S atoms at the O site of TiO2 HNS. The effects of functionalization and vacancy defects on the structural and electronic properties of HNS have been investigated by determining the corresponding projected density of states. It has been observed that functionalization causes a shift in the VBM and CBM of HNS, which in principle influences the catalytic activity. In addition, we have determined the work function for these materials in order to correlate them with the electrochemical activities of different considered HNSs. The catalytic activity has been predicted by determining the reaction coordinate as constructed from the free energies of the different reaction intermediates involved in HER and OER Among all of the systems that we have studied, HNS with an oxygen monovacancy has emerged as the best possible candidate for the water-splitting mechanism.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019
Keywords
TiO2 HNS, oxygen vacancy, hydrogen evolution, work function, free energy, reaction pathway
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-255772 (URN)10.1021/acsaem.9b00745 (DOI)000477074700056 ()2-s2.0-85070563486 (Scopus ID)
Note

QC 20190809

Available from: 2019-08-09 Created: 2019-08-09 Last updated: 2019-10-04Bibliographically approved
Bovornratanaraks, T., Tsuppayakorn-aek, P., Luo, W. & Ahuja, R. (2019). Ground-state structure of semiconducting and superconducting phases in xenon carbides at high pressure. Scientific Reports, 9, Article ID 2459.
Open this publication in new window or tab >>Ground-state structure of semiconducting and superconducting phases in xenon carbides at high pressure
2019 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 2459Article in journal (Refereed) Published
Abstract [en]

The 'missing Xe paradox' is one of the phenomena at the Earth's atmosphere. Studying the 'missing Xe paradox' will provide insights into a chemical reaction of Xe with C. We search the ground-state structure candidates of xenon carbides using the Universal Structure Predictor: Evolutionary Xtallography (USPEX) code, which has been successfully applied to a variety of systems. We predict that XeC2 is the most stable among the convex hull. We find that the I((4) over bar)2m structure of XeC2 is the semiconducting phase. Accurate electronic structures of tetragonal XeC2 have been calculated using a hybrid density functionals HSE06, which gives larger more accurate band gap than a GGA-PBE exchange-correlation functional. Specifically, we find that the I((4) over bar)2m structure of XeC2 is a dynamically stable structure at high pressure. We also predict that the P6/mmm structure of XeC2 is the superconducting phase with a critical temperature of 38 K at 200 GPa. The ground-state structure of xenon carbides is of critical importance for understanding in the missing Xe. We discuss the inference of the stable structures of XeC2. The accumulation of electrons between Xe and C led to the stability by investigating electron localization function (ELF).

Place, publisher, year, edition, pages
Nature Publishing Group, 2019
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-245911 (URN)10.1038/s41598-019-39176-4 (DOI)000459281500028 ()30792456 (PubMedID)2-s2.0-85061964206 (Scopus ID)
Note

QC 20190318

Available from: 2019-03-18 Created: 2019-03-18 Last updated: 2019-03-18Bibliographically approved
Pakeetood, P., Reunchan, P., Boonchun, A., Limpijumnong, S., Munprom, R., Ahuja, R. & T-Thienprasert, J. (2019). Hybrid-Functional Study of Native Defects and W/Mo-Doped in Monoclinic-Bismuth Vanadate. The Journal of Physical Chemistry C, 123(23), 14508-14516
Open this publication in new window or tab >>Hybrid-Functional Study of Native Defects and W/Mo-Doped in Monoclinic-Bismuth Vanadate
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2019 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 23, p. 14508-14516Article in journal (Refereed) Published
Abstract [en]

Monoclinic scheelite (ms) BiVO4 is recognized as one of the most promising photocatalyst materials due to its band gap as well as band-edge positions. Several theoretical and experimental works have been dedicated to improving the photocatalytic activity of ms-BiVO4. It has been reported that doping ms-BiVO4 with either W or Mo can enhance its photocatalytic activity compared to the undoped one. Further, codoping with W and Mo can improve the photocatalytic activity. Here, we systematically investigate all native and W/Mo-related defects in ms-BiVO4 by using density functional theory with hybrid functional. For undoped ms-BiVO4, we reveal that vacancies are the most dominant intrinsic defects and these defects compensate themselves leading to moderate n-type conductivity in O-poor growth condition. For W/Mo-doped ms-BiVO4, W and Mo are likely to substitute for V atom under all crystal growth conditions. While W v defect is a shallow donor, Mo v defect creates a defect level below the conduction band edge. This implies that doping with W can gain more photocatalytic efficiency, which agrees well with experiment. Interestingly, we find that two donors, i.e., W v and Mo v defects, prefer to form a complex defect becoming a shallow double donor. This can improve the electrical conductivity of W/Mo-codoped ms-BiVO4, which helps enhance its photocatalytic performance. In addition, the formation of donor-donor complexes is quite stable and helps improve material property.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2019
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-255199 (URN)10.1021/acs.jpcc.9b02698 (DOI)000471834000045 ()
Note

QC 20190904

Available from: 2019-09-04 Created: 2019-09-04 Last updated: 2019-09-04Bibliographically approved
Anikina, E., Banerjee, A., Beskachko, V. & Ahuja, R. (2019). Li-Functionalized Carbon Nanotubes for Hydrogen Storage: Importance of Size Effects. ACS APPLIED NANO MATERIALS, 2(5), 3021-3030
Open this publication in new window or tab >>Li-Functionalized Carbon Nanotubes for Hydrogen Storage: Importance of Size Effects
2019 (English)In: ACS APPLIED NANO MATERIALS, ISSN 2574-0970, Vol. 2, no 5, p. 3021-3030Article in journal (Refereed) Published
Abstract [en]

We investigated Li-doped carbon nanotubes (CNTs) as a promising hydrogen storage media. In this computational model, we considered isolated lithium atom adsorbed on a CNT wall as an adsorption site for hydrogen. We focused on the influence of size effects on the structural and energetic characteristics of CNT(n,n)@Li+kH(2) complexes where n = 5, 7, 9; k = 1,..., 6; N, = 4, 5, 6 (N-c is translation length of CNT, expressed in terms of a number of CNT unit cells). We proved that modeled CNT length substantially influences internal sorption of Li and hydrogen on the narrow tube (5,5), which subsequently alters the adsorption energies of H-2 molecules and causes the deformation of the carbon framework. Moreover, the size effects are not pronounced in the case of external sorption for all considered CNT translation lengths and diameters. We have not observed any noticeable qualitative difference between internal and external hydrogen sorption in the nanotube wider than CNT(5,5). In the case of external adsorption on all considered nanotubes, doping with Li increases hydrogen adsorption energies of up to four H-2 molecules by 100 meV in comparison with pure CNTs. And the local density approximation estimations (similar to 250 meV/H-2) of adsorption energy on Li-decorated CNTs exceed the lowest requirement proposed by the U.S. Department of Energy (200 meV/H-2). In the case of internal sorption on Li-functionalized tubes, the generalized gradient approximation also gives hydrogen adsorption energies in the desired range of 200-600 meV/H-2. However, steric hindrances could prevent sufficient hydrogen uptakes (less than 2 wt % inside CNT(5,5)). We believe that our findings on the size effects are important for estimation of CNT's hydrogen storage properties.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2019
Keywords
carbon nanotubes, hydrogen adsorption, Li-functionalization, DFT, periodic boundary condition
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-254030 (URN)10.1021/acsanm.9b00406 (DOI)000469410000049 ()
Note

QC 20190814

Available from: 2019-08-14 Created: 2019-08-14 Last updated: 2019-08-14Bibliographically approved
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