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  • 1.
    Jana, Somnath
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India;Helmholtz Zentrum Berlin FG ISRR, Albert Einstein Str 15, D-12489 Berlin, Germany.
    Panda, S. K.
    Univ Paris Saclay, Ctr Phys Theor, Ecole Polytech, CNRS UMR 7644, F-91128 Palaiseau, France;Bennett Univ, Dept Phys, Greater Noida 201310, Uttar Pradesh, India.
    Phuyal, Dibya
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Pal, B.
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Mukherjee, Soham
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Dutta, A.
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Anil Kumar, Puri
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Seagate Technol, 1 Disc Dr, Springtown BT48 0BF, North Ireland.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Schött, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Thunström, Patrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Kamalakar, M. Venkata
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Segre, Carlo U.
    IIT, CSRRI, Chicago, IL 60616 USA;IIT, Dept Phys, Chicago, IL 60616 USA.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Biermann, S.
    Univ Paris Saclay, Ctr Phys Theor, Ecole Polytech, CNRS UMR 7644, F-91128 Palaiseau, France;Coll France, 11 Pl Marcelin Berthelot, F-75005 Paris, France.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Orebro Univ, Sch Sci & Technol, SE-70182 Orebro, Sweden.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sarma, D. D.
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Charge disproportionate antiferromagnetism at the verge of the insulator-metal transition in doped LaFeO32019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 7, article id 075106Article in journal (Refereed)
    Abstract [en]

    We explore the effects of electron doping in lanthanum ferrite, LaFeO3 by doping Mo at the Fe sites. Based on magnetic, transport, scanning tunneling spectroscopy, and x-ray photoelectron spectroscopy measurements, we find that the large gap, charge-transfer, antiferromagnetic (AFM) insulator LaFeO3 becomes a small gap AFM band insulator at low Mo doping. With increasing doping concentration, Mo states, which appear around the Fermi level, is broadened and become gapless at a critical doping of 20%. Using a combination of calculations based on density functional theory plus Hubbard U (DFT+U) and x-ray absorption spectroscopy measurements, we find that the system shows charge disproportionation (CD) in Fe ions at 25% Mo doping, where two distinct Fe sites, having Fe2+ and Fe3+ nominal charge states appear. A local breathing-type lattice distortion induces the charge disproportionation at the Fe site without destroying the antiferromagnetic order. Our combined experimental and theoretical investigations establish that the Fe states form a CD antiferromagnet at 25% Mo doping, which remains insulating, while the appearance of Mo states around the Fermi level is showing an indication towards the insulator-metal transition.

  • 2.
    Johansson, Malin B
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Philippe, Bertrand
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Banerjee, Amitava
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Phuyal, Dibya
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Mukherjee, Soham
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Chakraborty, Sudip
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Cameau, Mathis
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Zhu, Huimin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Ahuja, Rajeev
    Uppsala Univ, Dept Phys & Astron, Mat Theory Div, Condensed Matter TRoyal Inst Technol, Dept Mat & Engn, Appl Mat Phys, S-10044 Stockholm, Sweden.
    Boschloo, Gerrit
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Rensmo, Håkan
    Johansson, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Cesium Bismuth Iodide Solar Cells from Systematic Molar Ratio Variation of CsI and BiI32019In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 58, no 18, p. 12040-12052Article in journal (Refereed)
    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.

  • 3.
    Phuyal, Dibya
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Mukherjee, Soham
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Das, Shyamashis
    Department of Solid State and Structural Chemistry Unit, Indian Institute of Science - Bengaluru 560012, India.
    Jana, Somnath
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Kvashnina, Kristina O.
    Rossendorf Beamline at ESRF - The European Synchrotron - CS40220, 38043 Grenoble Cedex 9, France; Helmholtz Zentrum Dresden-Rossendorf (HZDR), Institute of Resource Ecology - PO Box 510119, 01314 Dresden, Germany.
    Sarma, D.D.
    Department of Solid State and Structural Chemistry Unit, Indian Institute of Science - Bengaluru 560012, India.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Butorin, Sergei M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    The origin of low bandgap and ferroelectricity of a co-doped BaTiO32018In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 124, no 2, article id 27005Article in journal (Refereed)
    Abstract [en]

    We recently demonstrated the lowest bandgap bulk ferroelectric material, BaTi1-x(Mn1/2Nb1/2)xO3, a promising candidate material for visible light absorption in opto- electronic devices. Using a combination of x-ray spectroscopies and density functional theory (DFT) calculations, we here elucidate this compound’s electronic structure and the modifications induced by Mn doping. In particular, we are able to rationalize how this compound retains its ferroelectricity even through a significant reduction of the optical gap upon Mn doping. The local electronic structure and atomic coordination are investigated using x-ray absorption at the Ti K, Mn K, and O K edges, which suggests only small distortions to the parent tetragonal ferroelectric system, BaTiO3, thereby providing a clue to the substantial retention of ferroelectricity in spite of doping. Features at the Ti K edge, which are sensitive to local symmetry and an indication of Ti off-centering within the Ti-O6 octahedra, show modest changes with doping and strongly corroborates with our measured polarization values. Resonant photoelectron spectroscopy results suggest the origin of the reduction of the bandgap in terms of newly created Mn d bands that hybridize with O 2p states. X-ray absorption spectra at the O K-edge provide evidence for new states below the conduction band of the parent compound, illustrating additional contributions facilitating bandgap reduction.

  • 4.
    Phuyal, Dibya
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Mukherjee, Soham
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Jana, Somnath
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Denoel, Fernand
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Kamalakar, M. Venkata
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Butorin, Sergei M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Kalaboukhov, Alexei
    Department of Microtechnology and Nanoscience, Chalmers University of Technology, S-41296 Gothenburg, Sweden.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Ferroelectric properties of BaTiO3 thin films co-doped with Mn and Nb2019In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 9, no 9, article id 095207Article in journal (Refereed)
    Abstract [en]

    We report on properties of BaTiO3 thin films where the bandgap is tuned via aliovalent doping of Mn and Nb ions co-doped at the Ti site. The doped films show single-phase tetragonal structure, growing epitaxially with a smooth interface to the substrate. Using piezoforce microscopy, we find that both doped and undoped films exhibit good ferroelectric response. The piezoelectric domain switching in the films was confirmed by measuring local hysteresis of the polarization at several different areas across the thin films, demonstrating a switchable ferroelectric state. The doping of the BaTiO3 also reduces the bandgap of the material from 3.2 eV for BaTiO3 to nearly 2.7 eV for the 7.5% doped sample, suggesting the viability of the films for effective light harvesting in the visible spectrum. The results demonstrate co-doping as an effective strategy for bandgap engineering and a guide for the realization of visible-light applications using its ferroelectric properties.

  • 5.
    Wu, Hua
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström. ilin Univ, State Key Lab Integrated Optoelect, Changchun 130012, Jilin, Peoples R China;Jilin Univ, Coll Elect Sci & Engn, Changchun 130012, Jilin, Peoples R China.
    Zhu, Huimin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Erbing, Axel
    Stockholm Univ, Alballova Univ Ctr, Dept Phys, S-10691 Stockholm, Sweden.
    Johansson, Malin B
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Mukherjee, Soham
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Man, Gabriel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Odelius, Michael
    Stockholm Univ, Alballova Univ Ctr, Dept Phys, S-10691 Stockholm, Sweden.
    Johansson, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Bandgap Tuning of Silver Bismuth Iodide via Controllable Bromide Substitution for Improved Photovoltaic Performance2019In: ACS APPLIED ENERGY MATERIALSArticle in journal (Refereed)
    Abstract [en]

    In this work, silver-bismuth-halide thin films, exhibiting low toxicity and good stability, were explored systemically by gradually substituting iodide, I, with bromide, Br, in the AgBi2I7 system. It was found that the optical bandgap can be tuned by varying the I/Br ratio. Moreover, the film quality was improved when introducing a small amount of Br. The solar cell was demonstrated to be more stable at ambient conditions and most efficient when incorporating 10% Br, as a result of decreased recombination originating from the increased grain size. Thus, replacing a small amount of I with Br was beneficial for photovoltaic performance.

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