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Author Tsirlin, A.A.; Abakumov, A.M.; Van Tendeloo, G.; Rosner, H.
  Title (down) Interplay of atomic displacement in the quantum magnet (CuCI)LaNb2O7 Type A1 Journal article
  Year 2010 Publication Physical review : B : condensed matter and materials physics Abbreviated Journal Phys Rev B
  Volume 82 Issue 5 Pages 054107,1-054107,12
  Keywords A1 Journal article; Electron microscopy for materials research (EMAT)
  Abstract We report on the crystal structure of the quantum magnet CuClLaNb2O7 that was controversially described with respect to its structural organization and magnetic behavior. Using high-resolution synchrotron powder x-ray diffraction, electron diffraction, transmission electron microscopy, and band-structure calculations, we solve the room-temperature structure of this compound -CuClLaNb2O7 and find two high-temperature polymorphs. The -CuClLaNb2O7 phase, stable above 640 K, is tetragonal with asub=3.889 Å, csub =11.738 Å, and the space group P4/mmm. In the -CuClLaNb2O7 structure, the Cu and Cl atoms are randomly displaced from the special positions along the 100 directions. The phase asub2asubcsub, space group Pbmm and the phase 2asub2asubcsub, space group Pbam are stable between 640 K and 500 K and below 500 K, respectively. The structural changes at 500 and 640 K are identified as order-disorder phase transitions. The displacement of the Cl atoms is frozen upon the → transformation while a cooperative tilting of the NbO6 octahedra in the phase further eliminates the disorder of the Cu atoms. The low-temperature -CuClLaNb2O7 structure thus combines the two types of the atomic displacements that interfere due to the bonding between the Cu atoms and the apical oxygens of the NbO6 octahedra. The precise structural information resolves the controversy between the previous computation-based models and provides the long-sought input for understanding CuClLaNb2O7 and related compounds with unusual magnetic properties.
  Address
  Corporate Author Thesis
  Publisher Place of Publication Editor
  Language Wos 000280849400001 Publication Date 2010-08-12
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 1098-0121;1550-235X; ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 3.836 Times cited 13 Open Access
  Notes Approved Most recent IF: 3.836; 2010 IF: 3.774
  Call Number UA @ lucian @ c:irua:83991 Serial 1706
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Author O'Sullivan, M.; Hadermann, J.; Dyer, M.S.; Turner, S.; Alaria, J.; Manning, T.D.; Abakumov, A.M.; Claridge, J.B.; Rosseinsky, M.J.
  Title (down) Interface control by chemical and dimensional matching in an oxide heterostructure Type A1 Journal article
  Year 2016 Publication Nature chemistry Abbreviated Journal Nat Chem
  Volume 8 Issue 8 Pages 347-353
  Keywords A1 Journal article; Electron microscopy for materials research (EMAT)
  Abstract Interfaces between different materials underpin both new scientific phenomena, such as the emergent behaviour at oxide interfaces, and key technologies, such as that of the transistor. Control of the interfaces between materials with the same crystal structures but different chemical compositions is possible in many materials classes, but less progress has been made for oxide materials with different crystal structures. We show that dynamical self-organization during growth can create a coherent interface between the perovskite and fluorite oxide structures, which are based on different structural motifs, if an appropriate choice of cations is made to enable this restructuring. The integration of calculation with experimental observation reveals that the interface differs from both the bulk components and identifies the chemical bonding requirements to connect distinct oxide structures.
  Address
  Corporate Author Thesis
  Publisher Place of Publication Editor
  Language Wos 000372505500013 Publication Date 2016-02-01
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 1755-4330; 1755-4349 ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 25.87 Times cited 28 Open Access
  Notes Approved Most recent IF: 25.87
  Call Number UA @ lucian @ c:irua:133189 Serial 4199
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Author Zhang, B.; Dugas, R.; Rousse, G.; Rozier, P.; Abakumov, A.M.; Tarascon, J.-M.
  Title (down) Insertion compounds and composites made by ball milling for advanced sodium-ion batteries Type A1 Journal article
  Year 2016 Publication Nature communications Abbreviated Journal Nat Commun
  Volume 7 Issue 7 Pages 10308
  Keywords A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
  Abstract Sodium-ion batteries have been considered as potential candidates for stationary energy storage because of the low cost and wide availability of Na sources. However, their future commercialization depends critically on control over the solid electrolyte interface formation, as well as the degree of sodiation at the positive electrode. Here we report an easily scalable ball milling approach, which relies on the use of metallic sodium, to prepare a variety of sodium-based alloys, insertion layered oxides and polyanionic compounds having sodium in excess such as the Na4V2(PO4)(2)F-3 phase. The practical benefits of preparing sodium-enriched positive electrodes as reservoirs to compensate for sodium loss during solid electrolyte interphase formation are demonstrated by assembling full C/P'2-Na-1[Fe0.5Mn0.5]O-2 and C/'Na3+xV2(PO4)(2)F-3' sodium-ion cells that show substantial increases (>10%) in energy storage density. Our findings may offer electrode design principles for accelerating the development of the sodium-ion technology.
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  Corporate Author Thesis
  Publisher Place of Publication Editor
  Language Wos 000369021400002 Publication Date 2016-01-18
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 2041-1723 ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 12.124 Times cited 104 Open Access
  Notes Approved Most recent IF: 12.124
  Call Number UA @ lucian @ c:irua:131599 Serial 4197
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Author Shpanchenko, R.V.; Rozova, M.G.; Abakumov, A.M.; Ardashnikova, E.I.; Kovba, M.L.; Putilin, S.N.; Antipov, E.V.; Lebedev, O.I.; Van Tendeloo, G.
  Title (down) Inducing superconductivity and structural transformations by fluorination of reduced YBCO Type A1 Journal article
  Year 1997 Publication Physica: C : superconductivity Abbreviated Journal Physica C
  Volume 280 Issue Pages 272-280
  Keywords A1 Journal article; Electron microscopy for materials research (EMAT)
  Abstract
  Address
  Corporate Author Thesis
  Publisher Place of Publication Amsterdam Editor
  Language Wos A1997XX21600005 Publication Date 0000-00-00
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 0921-4534 ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 1.404 Times cited 35 Open Access
  Notes Approved Most recent IF: 1.404; 1997 IF: 2.199
  Call Number UA @ lucian @ c:irua:21449 Serial 1604
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Author Morozov, V.A.; Bertha, A.; Meert, K.W.; Van Rompaey, S.; Batuk, D.; Martinez, G.T.; Van Aert, S.; Smet, P.F.; Raskina, M.V.; Poelman, D.; Abakumov, A.M.; Hadermann, J.;
  Title (down) Incommensurate modulation and luminescence in the CaGd2(1-x)Eu2x(MoO4)4(1-y)(WO)4y (0\leq x\leq1, 0\leq y\leq1) red phosphors Type A1 Journal article
  Year 2013 Publication Chemistry of materials Abbreviated Journal Chem Mater
  Volume 25 Issue 21 Pages 4387-4395
  Keywords A1 Journal article; Electron microscopy for materials research (EMAT)
  Abstract Scheelite related compounds (A',A '') [(B',B '')O-4], with B', B '' = W and/or Mo are promising new light-emitting materials for photonic applications, including phosphor converted LEDs (light-emitting diodes). In this paper, the creation and ordering of A-cation vacancies and the effect of cation substitutions in the scheelite-type framework are investigated as a factor for controlling the scheelite-type structure and luminescent properties. CaGd2(1-x)Eu2x(MoO4)(4(1-y))(WO4)(4y) (0 <= x <= 1, 0 <= y <= 1) solid solutions with scheelite-type structure were synthesized by a solid state method, and their structures were investigated using a combination of transmission electron microscopy techniques and powder X-ray diffraction. Within this series all complex molybdenum oxides have (3 + 2)D incommensurately modulated structures with superspace group I4(1)/a(alpha,beta,0)00(-beta,alpha,0)00, while the structures of all tungstates are (3 + 1)D incommensurately modulated with superspace group I2/b(alpha beta 0)00. In both cases the modulation arises because of cation-vacancy ordering at the A site. The prominent structural motif is formed by columns of A-site vacancies running along the c-axis. These vacant columns occur in rows of two or three aligned along the [110] direction of the scheelite subcell. The replacement of the smaller Gd3+ by the larger Eu3+ at the A-sublattice does not affect the nature of the incommensurate modulation, but an increasing replacement of Mo6+ by W6+ switches the modulation from (3 + 2)D to (3 + 1)D regime. Thus, these solid solutions can be considered as a model system where the incommensurate modulation can be monitored as a function of cation nature while the number of cation vacancies at the A sites remain constant upon the isovalent cation replacement. All compounds' luminescent properties were measured, and the optical properties were related to the structural properties of the materials. CaGd2(1-x)(MoO4)(4(1-y))(WO4)(4y) phosphors emit intense red light dominated by the D-5(0)-F-7(2) transition at 612 nm, along with other transitions from the D-5(1) and D-5(0) excited states. The intensity of the 5D0-7F2 transition reaches a maximum at x = 0.5 for y = 0 and 1.
  Address
  Corporate Author Thesis
  Publisher Place of Publication Washington, D.C. Editor
  Language Wos 000327045000030 Publication Date 2013-09-24
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 0897-4756;1520-5002; ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 9.466 Times cited 63 Open Access
  Notes Approved Most recent IF: 9.466; 2013 IF: 8.535
  Call Number UA @ lucian @ c:irua:112776 Serial 1594
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Author Karakulina, O.M.; Demortière, A.; Dachraoui, W.; Abakumov, A.M.; Hadermann, J.
  Title (down) In Situ Electron Diffraction Tomography Using a Liquid-Electrochemical Transmission Electron Microscopy Cell for Crystal Structure Determination of Cathode Materials for Li-Ion batteries Type A1 Journal article
  Year 2018 Publication Nano letters Abbreviated Journal Nano Lett
  Volume 18 Issue 10 Pages 6286-6291
  Keywords A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
  Abstract We demonstrate that changes in the unit cell structure of lithium battery cathode materials during electrochemical cycling in liquid electrolyte can be determined for particles of just a few hundred nanometers in size using in situ transmission electron microscopy (TEM). The atomic coordinates, site occupancies (including lithium occupancy), and cell parameters of the materials can all be reliably quantified. This was achieved using electron diffraction tomography (EDT) in a sealed electrochemical cell with conventional liquid electrolyte (LP30) and LiFePO4 crystals, which have a well-documented charged structure to use as reference. In situ EDT in a liquid environment cell provides a viable alternative to in situ X-ray and neutron diffraction experiments due to the more local character of TEM, allowing for single crystal diffraction data to be obtained from multiphased powder samples and from submicrometer- to nanometer-sized particles. EDT is the first in situ TEM technique to provide information at the unit cell level in the liquid environment of a commercial TEM electrochemical cell. Its application to a wide range of electrochemical experiments in liquid environment cells and diverse types of crystalline materials can be envisaged.
  Address
  Corporate Author Thesis
  Publisher Place of Publication Editor
  Language Wos 000447355400024 Publication Date 2018-10-10
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 1530-6984 ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 12.712 Times cited 12 Open Access Not_Open_Access: Available from 08.09.2019
  Notes O.M. Karakulina, A.M. Abakumov and J. Hadermann acknowledge support from FWO under grant G040116N. A. Demortière wants to thank the French network on the electrochemical energy storage (RS2E), the Store-Ex Labex, for the financial support. Finally, the Fonds Européen de Développement Régional (FEDER), CNRS, Région Hauts-de-France, and Ministère de l’Education Nationale de l’Enseignement Supérieur et de la Recherche are acknowledged for funding. Approved Most recent IF: 12.712
  Call Number EMAT @ emat @c:irua:154750 Serial 5063
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Author Dubrovinsky, L.; Dubrovinskaia, N.; Prakapenka, V.B.; Abakumov, A.M.
  Title (down) Implementation of micro-ball nanodiamond anvils for high-pressure studies above 6 Mbar Type A1 Journal article
  Year 2012 Publication Nature communications Abbreviated Journal Nat Commun
  Volume 3 Issue Pages 1163-1167
  Keywords A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
  Abstract Since invention of the diamond anvil cell technique in the late 1950s for studying materials at extreme conditions, the maximum static pressure generated so far at room temperature was reported to be about 400 GPa. Here we show that use of micro-semi-balls made of nanodiamond as second-stage anvils in conventional diamond anvil cells drastically extends the achievable pressure range in static compression experiments to above 600 GPa. Micro-anvils (10-50 mu m in diameter) of superhard nano-diamond (with a grain size below similar to 50 nm) were synthesized in a large volume press using a newly developed technique. In our pilot experiments on rhenium and gold we have studied the equation of state of rhenium at pressures up to 640 GPa and demonstrated the feasibility and crucial necessity of the in situ ultra high-pressure measurements for accurate determination of material properties at extreme conditions.
  Address
  Corporate Author Thesis
  Publisher Place of Publication Editor
  Language Wos 000313514100073 Publication Date 2012-10-23
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 2041-1723; ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 12.124 Times cited 150 Open Access
  Notes Approved Most recent IF: 12.124; 2012 IF: 10.015
  Call Number UA @ lucian @ c:irua:110134 Serial 1563
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Author Hadermann, J.; Van Tendeloo, G.; Abakumov, A.M.; Rozova, M.G.; Antipov, E.V.
  Title (down) HREM study of fluorinated Nd2CuO4 Type A1 Journal article
  Year 2001 Publication Journal of solid state chemistry Abbreviated Journal J Solid State Chem
  Volume 157 Issue Pages 56-61
  Keywords A1 Journal article; Electron microscopy for materials research (EMAT)
  Abstract
  Address
  Corporate Author Thesis
  Publisher Place of Publication London Editor
  Language Wos 000167634500008 Publication Date 2002-09-18
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 0022-4596; ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 2.299 Times cited 7 Open Access
  Notes Approved Most recent IF: 2.299; 2001 IF: 1.614
  Call Number UA @ lucian @ c:irua:36047 Serial 1510
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Author Stefan, M.; Nistor, S.V.; Mateescu, D.C.; Abakumov, A.M.
  Title (down) Growth of pure and doped Rb2ZnCl4and K2ZnCl4 single crystals by Czochralski technique Type A1 Journal article
  Year 1999 Publication Journal of crystal growth Abbreviated Journal J Cryst Growth
  Volume 200 Issue 1-2 Pages 148-154
  Keywords A1 Journal article; Electron microscopy for materials research (EMAT)
  Abstract High-quality single crystals of Rb2ZnCl4 and K2ZnCl4, pure or doped with Cu, Mn, Cd, Tl, Sn, Pb and In cations, were grown by Czochralski technique in argon atmosphere, using an experimental setup that allows direct visual access to the whole growth zone. Slowly cooled crystals exhibit excellent cleavage properties. Fastly cooled crystals do cleave poorly. As shown by X-ray diffraction studies, such K2ZnCl4 samples exhibit inclusions of the high-temperature Pmcn phase with lattice parameters a = 7.263(2) Angstrom, b = 12.562(2) Angstrom and c = 8.960(4) Angstrom in the P2(1) cn room temperature stable phase. ESR and optical spectroscopy studies revealed the localization and valence state of the cation dopants. (C) 1999 Elsevier Science B.V. All rights reserved.
  Address
  Corporate Author Thesis
  Publisher Place of Publication Amsterdam Editor
  Language Wos 000079840600021 Publication Date 2002-07-25
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 0022-0248; ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 1.751 Times cited 13 Open Access
  Notes Approved Most recent IF: 1.751; 1999 IF: 1.492
  Call Number UA @ lucian @ c:irua:102909 Serial 1395
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Author Abakumov, A.M.; Li, C.; Boev, A.; Aksyonov, D.A.; Savina, A.A.; Abakumova, T.A.; Van Tendeloo, G.; Bals, S.
  Title (down) Grain boundaries as a diffusion-limiting factor in lithium-rich NMC cathodes for high-energy lithium-ion batteries Type A1 Journal article
  Year 2021 Publication ACS applied energy materials Abbreviated Journal
  Volume 4 Issue 7 Pages 6777-6786
  Keywords A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
  Abstract High-energy lithium-rich layered transition metal oxides are capable of delivering record electrochemical capacity and energy density as positive electrodes for Li-ion batteries. Their electrochemical behavior is extremely complex due to sophisticated interplay between crystal structure, electronic structure, and defect structure. Here we unravel an extra level of this complexity by revealing that the most typical representative Li1.2Ni0.13Mn0.54Co0.13O2 material, prepared by a conventional coprecipitation technique with Na2CO3 as a precipitating agent, contains abundant coherent (001) grain boundaries with a Na-enriched P2-structured block due to segregation of the residual sodium traces. The trigonal prismatic oxygen coordination of Na triggers multiple nanoscale twinning, giving rise to incoherent (104) boundaries. The cationic layers at the (001) grain boundaries are filled with transition metal cations being Mn-depleted and Co-enriched; this makes them virtually not permeable for the Li+ cations, and therefore they negatively influence the Li diffusion in and out of the spherical agglomerates. These results demonstrate that besides the mechanisms intrinsic to the crystal and electronic structure of Li-rich cathodes, their rate capability might also be depreciated by peculiar microstructural aspects. Dedicated engineering of grain boundaries opens a way for improving inherently sluggish kinetics of these materials.
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  Corporate Author Thesis
  Publisher Place of Publication Editor
  Language Wos 000678382900042 Publication Date 2021-07-02
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 2574-0962 ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor Times cited 4 Open Access OpenAccess
  Notes We thank Dr. M. V. Berekchiian (MSU) for assisting in ICPMS measurements. We acknowledge Russian Science Foundation (Grant 20-43-01012) and Research Foundation Flanders (FWO Vlaanderen, Project No. G0F1320N) for financial support. Approved Most recent IF: NA
  Call Number UA @ admin @ c:irua:180556 Serial 6841
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Author Tsirlin, A.A.; Nath, R.; Abakumov, A.M.; Shpanchenko, R.V.; Geibel, C.; Rosner, H.
  Title (down) Frustrated square lattice with spatial anisotropy: crystal structure and magnetic properties of PbZnVO(PO4)2 Type A1 Journal article
  Year 2010 Publication Physical review : B : condensed matter and materials physics Abbreviated Journal Phys Rev B
  Volume 81 Issue 17 Pages 174424,1-174424,13
  Keywords A1 Journal article; Electron microscopy for materials research (EMAT)
  Abstract Crystal structure and magnetic properties of the layered vanadium phosphate PbZnVO(PO4)2 are studied using x-ray powder diffraction, magnetization and specific-heat measurements, as well as band-structure calculations. The compound resembles AA′VO(PO4)2 vanadium phosphates and fits to the extended frustrated square-lattice model with the couplings J1, J1′ between nearest neighbors and J2, J2′ between next-nearest neighbors. The temperature dependence of the magnetization yields estimates of averaged nearest-neighbor and next-nearest-neighbor couplings, J̅ 1≃−5.2 K and J̅ 2≃10.0 K, respectively. The effective frustration ratio α=J̅ 2/J̅ 1 amounts to −1.9 and suggests columnar antiferromagnetic ordering in PbZnVO(PO4)2. Specific-heat data support the estimates of J̅ 1 and J̅ 2 and indicate a likely magnetic ordering transition at 3.9 K. However, the averaged couplings underestimate the saturation field, thus pointing to the spatial anisotropy of the nearest-neighbor interactions. Band-structure calculations confirm the identification of ferromagnetic J1, J1′ and antiferromagnetic J2, J2′ in PbZnVO(PO4)2 and yield (J1′−J1)≃1.1 K in excellent agreement with the experimental value of 1.1 K, deduced from the difference between the expected and experimentally measured saturation fields. Based on the comparison of layered vanadium phosphates with different metal cations, we show that a moderate spatial anisotropy of the frustrated square lattice has minor influence on the thermodynamic properties of the model. We discuss relevant geometrical parameters, controlling the exchange interactions in these compounds and propose a strategy for further design of strongly frustrated square-lattice materials.
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  Corporate Author Thesis
  Publisher Place of Publication Editor
  Language Wos 000278141600082 Publication Date 2010-05-25
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 1098-0121;1550-235X; ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 3.836 Times cited 27 Open Access
  Notes Approved Most recent IF: 3.836; 2010 IF: 3.774
  Call Number UA @ lucian @ c:irua:83384 Serial 1294
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Author Abakumov, A.M.; Batuk, D.; Tsirlin, A.A.; Prescher, C.; Dubrovinsky, L.; Sheptyakov, D.V.; Schnelle, W.; Hadermann, J.; Van Tendeloo, G.
  Title (down) Frustrated pentagonal Cairo lattice in the non-collinear antiferromagnet Bi4Fe5O13F Type A1 Journal article
  Year 2013 Publication Physical review : B : condensed matter and materials physics Abbreviated Journal Phys Rev B
  Volume 87 Issue 2 Pages 024423-24429
  Keywords A1 Journal article; Electron microscopy for materials research (EMAT)
  Abstract We report on the crystal structure and magnetism of the iron-based oxyfluoride Bi4Fe5O13F, a material prototype of the Cairo pentagonal spin lattice. The crystal structure of Bi4Fe5O13F is determined by a combination of neutron diffraction, synchrotron x-ray diffraction, and transmission electron microscopy. It comprises layers of FeO6 octahedra and FeO4 tetrahedra forming deformed pentagonal units. The topology of these layers resembles a pentagonal least-perimeter tiling, which is known as the Cairo lattice. This topology gives rise to frustrated exchange couplings and underlies a sequence of magnetic transitions at T-1 = 62 K, T-2 = 71 K, and T-N = 178 K, as determined by thermodynamic measurements and neutron diffraction. Below T-1, Bi4Fe5O13F forms a fully ordered non-collinear antiferromagnetic structure, whereas the magnetic state between T-1 and T-N may be partially disordered according to the sizable increase in the magnetic entropy at T-1 and T-2. Bi4Fe5O13F reveals unanticipated magnetic transitions on the pentagonal Cairo spin lattice and calls for a further work on finite-temperature properties of this strongly frustrated spin model. DOI: 10.1103/PhysRevB.87.024423
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  Corporate Author Thesis
  Publisher Place of Publication Editor
  Language Wos 000314224800002 Publication Date 2013-02-01
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 1098-0121;1550-235X; ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 3.836 Times cited 17 Open Access
  Notes Approved Most recent IF: 3.836; 2013 IF: 3.664
  Call Number UA @ lucian @ c:irua:107688 Serial 1293
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Author Abakumov, A.M.; Erni, R.; Tsirlin, A.A.; Rossell, M.D.; Batuk, D.; Nénert, G.; Van Tendeloo, G.
  Title (down) Frustrated octahedral tilting distortion in the incommensurately modulated Li3xNd2/3-xTiO3 perovskites Type A1 Journal article
  Year 2013 Publication Chemistry of materials Abbreviated Journal Chem Mater
  Volume 25 Issue 13 Pages 2670-2683
  Keywords A1 Journal article; Electron microscopy for materials research (EMAT)
  Abstract Perovskite-structured titanates with layered A-site ordering form remarkably complex superstructures. Using transmission electron microscopy, synchrotron X-ray and neutron powder diffraction, and ab initio structure relaxation, we present the structural solution of the incommensurately modulated Li3xNd2/3xTiO3 perovskites (x = 0.05, superspace group Pmmm(α1,1/2,0)000(1/2,β2 0)000, a = 3.831048(5) Å, b = 3.827977(4) Å, c = 7.724356(8) Å, q1 = 0.45131(8)a* + 1/2b*, q2 = 1/2a* + 0.41923(4)b*). In contrast to earlier conjectures on the nanoscale compositional phase separation in these materials, all peculiarities of the superstructure can be understood in terms of displacive modulations related to an intricate octahedral tilting pattern. It involves fragmenting the pattern of the out-of-phase tilted TiO6 octahedra around the a- and b-axes into antiphase domains, superimposed on the pattern of domains with either pronounced or suppressed in-phase tilt component around the c-axis. The octahedral tilting competes with the second order JahnTeller distortion of the TiO6 octahedra. This competition is considered as the primary driving force for the modulated structure. The A cations are suspected to play a role in this modulation affecting it mainly through the tolerance factor and the size variance. The reported crystal structure calls for a revision of the structure models proposed for the family of layered A-site ordered perovskites exhibiting a similar type of modulated structure.
  Address
  Corporate Author Thesis
  Publisher Place of Publication Washington, D.C. Editor
  Language Wos 000321809700015 Publication Date 2013-06-04
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 0897-4756;1520-5002; ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 9.466 Times cited 23 Open Access
  Notes Countatoms Approved Most recent IF: 9.466; 2013 IF: 8.535
  Call Number UA @ lucian @ c:irua:109216 Serial 1292
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Author Serov, T.V.; Dombrovski, E.N.; Ardashnikova, E.I.; Dolgikh, V.A.; el Omari, M.; el Omari, M.; Abaouz, A.; Senegas, J.; Chaban, N.G.; Abakumov, A.M.; Van Tendeloo, G.
  Title (down) Fluorite-like phases in the BaF2-BiF3-Bi2O3 system-synthesis, conductivity and defect clustering Type A1 Journal article
  Year 2005 Publication Materials research bulletin Abbreviated Journal Mater Res Bull
  Volume 40 Issue 5 Pages 821-830
  Keywords A1 Journal article; Electron microscopy for materials research (EMAT)
  Abstract
  Address
  Corporate Author Thesis
  Publisher Place of Publication New York, N.Y. Editor
  Language Wos 000229376500012 Publication Date 2005-03-01
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 0025-5408; ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 2.446 Times cited 4 Open Access
  Notes Iap V-1 Approved Most recent IF: 2.446; 2005 IF: 1.380
  Call Number UA @ lucian @ c:irua:54838 Serial 1240
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Author Navulla, A.; Tsirlin, A.A.; Abakumov, A.M.; Shpanchenko, R.V.; Zhang, H.; Dikarev, E.V.
  Title (down) Fluorinated heterometallic \beta-diketonates as volatile single-source precursors for the synthesis of low-valent mixed-metal fluorides Type A1 Journal article
  Year 2011 Publication Journal of the American Chemical Society Abbreviated Journal J Am Chem Soc
  Volume 133 Issue 4 Pages 692-694
  Keywords A1 Journal article; Electron microscopy for materials research (EMAT)
  Abstract Hexafluoroacetylacetonates that contain lead and divalent first-row transition metals, PbM(hfac)4 (M = Ni (1), Co (2), Mn (3), Fe (4), and Zn (5)), have been synthesized. Their heterometallic structures are held together by strong Lewis acid−base interactions between metal atoms and diketonate ligands acting in chelating−bridging fashion. Compounds 1−5 are highly volatile and decompose below 350 °C. Fluorinated heterometallic β-diketonates have been used for the first time as volatile single-source precursors for the preparation of mixed-metal fluorides. Complex fluorides of composition Pb2MF6 have been obtained by decomposition of 1−5 in a two-zone furnace under low-pressure nitrogen flow. Lead−transition metal fluorides conform to orthorhombically distorted Aurivillius-type structure with layers of corner-sharing [MF6] octahedra separated by α-PbO-type (Pb2F2) blocks. Pb2NiF6 and Pb2CoF6 were found to exhibit magnetic ordering below 80 and 43 K, respectively. The ordering is antiferromagnetic, with a weak, uncompensated moment due to the canting of spins. The Pb2MF6 fluorides represent a new class of prospective magnetoelectric materials combining transition metals and lone-pair main-group cations.
  Address
  Corporate Author Thesis
  Publisher Place of Publication Washington, D.C. Editor
  Language Wos 000287295300015 Publication Date 2010-12-21
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 0002-7863;1520-5126; ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 13.858 Times cited 28 Open Access
  Notes Approved Most recent IF: 13.858; 2011 IF: 9.907
  Call Number UA @ lucian @ c:irua:88820 Serial 1236
Permanent link to this record
 

 
Author Zaikina, J.V.; Batuk, M.; Abakumov, A.M.; Navrotsky, A.; Kauziarich, S.M.
  Title (down) Facile synthesis of Ba1-xKxFe2As2 superconductors via hydride route Type A1 Journal article
  Year 2014 Publication Journal of the American Chemical Society Abbreviated Journal J Am Chem Soc
  Volume 136 Issue 48 Pages 16932-16939
  Keywords A1 Journal article; Electron microscopy for materials research (EMAT)
  Abstract We have developed a fast, easy, and scalable synthesis method for Ba1xKxFe2As2 (0 ≤ x ≤ 1) superconductors using hydrides BaH2 and KH as a source of barium and potassium metals. Synthesis from hydrides provides better mixing and easier handling of the starting materials, consequently leading to faster reactions and/or lower synthesis temperatures. The reducing atmosphere provided by the evolved hydrogen facilitates preparation of oxygen-free powders. By a combination of methods we have shown that Ba1xKxFe2As2 obtained via hydride route has the same characteristics as when it is prepared by traditional solid-state synthesis. Refinement from synchrotron powder X-ray diffraction data confirms a linear dependence of unit cell parameters upon K content as well as the tetragonal to orthorhombic transition at low temperatures for compositions with x < 0.2. Magnetic measurements revealed dome-like dependence of superconducting transition temperature Tc upon K content with a maximum of 38 K for x close to 0.4. Electron diffraction and high-resolution high-angle annular dark-field scanning transmission electron microscopy indicates an absence of Ba/K ordering, while local inhomogeneity in the Ba/K distribution takes place at a scale of several angstroms along [110] crystallographic direction.
  Address
  Corporate Author Thesis
  Publisher Place of Publication Washington, D.C. Editor
  Language Wos 000345883900040 Publication Date 2014-11-11
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 0002-7863;1520-5126; ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 13.858 Times cited 13 Open Access
  Notes Approved Most recent IF: 13.858; 2014 IF: 12.113
  Call Number UA @ lucian @ c:irua:121331 Serial 1169
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Author Kirsanova, M.A.; Olenev, A.V.; Abakumov, A.M.; Bykov, M.A.; Shevelkov, A.V.
  Title (down) Extension of the clathrate family : the type X clathrate Ge79P29S18Te6 Type A1 Journal article
  Year 2011 Publication Angewandte Chemie: international edition in English Abbreviated Journal Angew Chem Int Edit
  Volume 50 Issue 10 Pages 2371-2374
  Keywords A1 Journal article; Electron microscopy for materials research (EMAT)
  Abstract Now they are 10! The title compound displays a new type of crystal structure and is labeled clathrate X according to the general classification of clathrate structures. In contrast to typical clathrates, this compound has three-coordinate atoms within the framework and combines distorted 24-vertex polyhedra (see picture, green) centered around tellurium guest atoms with very irregular 10-vertex polyhedra around sulfur atoms (yellow).
  Address
  Corporate Author Thesis
  Publisher Place of Publication Weinheim Editor
  Language Wos 000288036300033 Publication Date 2011-01-31
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 1433-7851; ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 11.994 Times cited 23 Open Access
  Notes Approved Most recent IF: 11.994; 2011 IF: 13.455
  Call Number UA @ lucian @ c:irua:88793 Serial 1158
Permanent link to this record
 

 
Author Hadermann, J.; Abakumov, A.M.; Tsirlin, A.A.; Rozova, M.G.; Sarakinou, E.; Antipov, E.V.
  Title (down) Expanding the Ruddlesden-Popper manganite family : the n=3 La3.2Ba0.8Mn3O10 Member Type A1 Journal article
  Year 2012 Publication Inorganic chemistry Abbreviated Journal Inorg Chem
  Volume 51 Issue 21 Pages 11487-11492
  Keywords A1 Journal article; Electron microscopy for materials research (EMAT)
  Abstract La3.2Ba0.8Mn3O10, a representative of the rare n = 3 members of the Ruddlesden-Popper manganites A(n+1)Mn(n)O(3n+1), was synthesized in an evacuated sealed silica tube. Its crystal structure was refined from a combination of powder X-ray diffraction (PXD) and precession electron diffraction (PED) data, with the rotations of the MnO6 octahedra described within the symmetry-adapted mode approach (space group Cccm, a = 29.068(1) angstrom, b = 5.5504(5) angstrom, c = 5.5412(5) angstrom; PXD RF = 0.053, RP = 0.026; PED RF = 0.248). The perovskite block in La3.2Ba0.8Mn3O10 features an octahedral tilting distortion with out-of-phase rotations of the Mn06 octahedra according to the (Phi,Phi,0)(Phi,Phi,0) mode, observed for the first time in the n = 3 Ruddlesden-Popper structures. The Mn06 octahedra demonstrate a noticeable deformation with the elongation of two apical Mn-O bonds due to the Jahn-Teller effect in the Mn3+ cations. The relationships between the octahedral tilting distortion, the ionic radii of the cations at the A- and B-positions, and the mismatch between the perovslcite and rock-salt blocks of the Ruddlesden-Popper structure are discussed. At low temperatures, La3.2Ba0.8Mn3O10 reveals a sizable remnant magnetization of about 1.3 mu(B)/Mn at 2K, and shows signatures of spin freezing below 150 K.
  Address
  Corporate Author Thesis
  Publisher Place of Publication Easton, Pa Editor
  Language Wos 000313220200036 Publication Date 2012-10-17
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 0020-1669;1520-510X; ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 4.857 Times cited 2 Open Access
  Notes Approved Most recent IF: 4.857; 2012 IF: 4.593
  Call Number UA @ lucian @ c:irua:110121 Serial 1133
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Author Bourgeois, J.; Hervieu, M.; Poienar, M.; Abakumov, A.M.; Elkaïm, E.; Sougrati, M.T.; Porcher, F.; Damay, F.; Rouquette, J.; Van Tendeloo, G.; Maignan, A.; Haines, J.; Martin, C.;
  Title (down) Evidence of oxygen-dependent modulation in LuFe2O4 Type A1 Journal article
  Year 2012 Publication Physical review : B : condensed matter and materials physics Abbreviated Journal Phys Rev B
  Volume 85 Issue 6 Pages 064102-064120,10
  Keywords A1 Journal article; Electron microscopy for materials research (EMAT)
  Abstract A polycrystalline sample of LuFe2O4 has been investigated by means of powder synchrotron x-ray and neutron diffraction and transmission electron microscopy (TEM), along with Mössbauer spectroscopy and transport and magnetic properties. A monoclinic distortion is unambiguously evidenced, and the crystal structure is refined in the monoclinic C2/m space group [aM = 5.9563(1) Å, bM = 3.4372(1) Å, cM = 8.6431(1) Å, β = 103.24(1)°]. Along with the previously reported modulations distinctive of the charge-ordering (CO) of the iron species, a new type of incommensurate order is observed, characterized by a vector q⃗1 = α1a⃗M* + γ1c⃗M* (with α1 ≅ 0.55, γ1 ≅ 0.13). In situ heating TEM observations from 300 to 773 K confirm that the satellites associated with q⃗1 vanish completely, only at a temperature significantly higher than the CO temperature. This incommensurate modulation has a displacive character and corresponds primarily to a transverse displacive modulation wave of the Lu cations position, as revealed by the high resolution, high angle annular dark field scanning TEM images and in agreement with synchrotron data refinements. Analyses of vacuum-annealed samples converge toward the hypothesis of a new ordering mechanism, associated with a tiny oxygen deviation from the O4 stoichiometry.
  Address
  Corporate Author Thesis
  Publisher Place of Publication Editor
  Language Wos 000299896900003 Publication Date 2012-02-06
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 1098-0121;1550-235X; ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 3.836 Times cited 24 Open Access
  Notes Hercules Approved Most recent IF: 3.836; 2012 IF: 3.767
  Call Number UA @ lucian @ c:irua:95042 Serial 1095
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Author Pearce, P.E.; Perez, A.J.; Rousse, G.; Saubanère, M.; Batuk, D.; Foix, D.; McCalla, E.; Abakumov, A.M.; Van Tendeloo, G.; Doublet, M.-L.; Tarascon, J.-M.
  Title (down) Evidence for anionic redox activity in a tridimensional-ordered Li-rich positive electrode β-Li2IrO3 Type A1 Journal article
  Year 2017 Publication Nature materials Abbreviated Journal Nat Mater
  Volume 16 Issue 5 Pages 580-586
  Keywords A1 Journal article; Electron microscopy for materials research (EMAT)
  Abstract Lithium-ion battery cathode materials have relied on cationic redox reactions until the recent discovery of anionic redox activity in Li-rich layered compounds which enables capacities as high as 300 mAh g(-1). In the quest for new high-capacity electrodes with anionic redox, a still unanswered question was remaining regarding the importance of the structural dimensionality. The present manuscript provides an answer. We herein report on a beta-Li2IrO3 phase which, in spite of having the Ir arranged in a tridimensional (3D) framework instead of the typical two-dimensional (2D) layers seen in other Li-rich oxides, can reversibly exchange 2.5 e(-) per Ir, the highest value ever reported for any insertion reaction involving d-metals. We show that such a large activity results from joint reversible cationic (Mn+) and anionic (O-2)(n-) redox processes, the latter being visualized via complementary transmission electron microscopy and neutron diffraction experiments, and confirmed by density functional theory calculations. Moreover, beta-Li2IrO3 presents a good cycling behaviour while showing neither cationic migration nor shearing of atomic layers as seen in 2D-layered Li-rich materials. Remarkably, the anionic redox process occurs jointly with the oxidation of Ir4+ at potentials as low as 3.4 V versus Li+/Li-0, as equivalently observed in the layered alpha-Li2IrO3 polymorph. Theoretical calculations elucidate the electrochemical similarities and differences of the 3D versus 2D polymorphs in terms of structural, electronic and mechanical descriptors. Our findings free the structural dimensionality constraint and broaden the possibilities in designing high-energy-density electrodes for the next generation of Li-ion batteries.
  Address
  Corporate Author Thesis
  Publisher Place of Publication Editor
  Language Wos 000400004200018 Publication Date 2017-02-27
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 1476-1122 ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 39.737 Times cited Open Access Not_Open_Access
  Notes The authors thank Q. Jacquet for fruitful discussions and V. Pomjakushin for his valuable help in neutron diffraction experiments. This work is based on experiments performed at the Swiss Spallation Neutron Source SINQ, Paul Scherrer Institute, Villigen, Switzerland. Use of the 11-BM mail service of the APS at Argonne National Laboratory was supported by the US Department of Energy under contract No. DE-AC02-06CH11357 and is greatly acknowledged. J.-M.T. acknowledges funding from the European Research Council (ERC) (FP/2014)/ERC Grant-Project 670116-ARPEMA. E.M. acknowledges financial support from the Fonds de Recherche du Quebec-Nature et Technologies. Approved Most recent IF: 39.737
  Call Number EMAT @ emat @c:irua:147502 Serial 4773
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Author Kolchina, L. M.; Lyskov, N.V.; Kuznetsov, A.N.; Kazakov, S.M.; Galin, M.Z.; Meledin, A.; Abakumov, A.M.; Bredikhin, S.I.; Mazo, G.N.; Antipov, E.V.
  Title (down) Evaluation of Ce-doped Pr2CuO4for potential application as a cathode material for solid oxide fuel cells Type A1 Journal article
  Year 2016 Publication RSC advances Abbreviated Journal Rsc Adv
  Volume 6 Issue 6 Pages 101029-101037
  Keywords A1 Journal article; Electron microscopy for materials research (EMAT)
  Abstract Pr2−xCexCuO4 (x = 0.05; 0.1; 0.15) samples were synthesized and systematically characterized towards application as a cathode material for solid oxide fuel cells (SOFCs). High-temperature electrical conductivity, thermal expansion, and electrocatalytic activity in the oxygen reduction reaction (ORR) were examined. The electrical conductivity of Pr2−xCexCuO4 oxides demonstrates semiconducting behavior up to 900 °C. Small Ce-doping (2.5 at%) allows an increase in electrical conductivity from 100 to 130 S cm−1 in air at 500–800 °C. DFT calculations revealed that the density of states directly below the Fermi level, comprised mainly of Cu 3d and O 2p states, is significantly affected by atoms in rare earth positions, which might give an indication of a correlation between calculated electronic structures and measured conducting properties. Ce-doping in Pr2−xCexCuO4 slightly increases TEC from 11.9 × 10−6 K−1 for x = 0 to 14.2 × 10−6 K−1 for x = 0.15. Substitution of 2.5% of Pr atoms in Pr2CuO4 by Ce is effective to enhance the electrochemical performance of the material as a SOFC cathode in the ORR (ASR of Pr1.95Ce0.05CuO4 electrode applied on Ce0.9Gd0.1O1.95 electrolyte is 0.39 Ω cm2 at 750 °C in air). The peak power density achieved for the electrolyte-supported fuel cell with the Pr1.95Ce0.05CuO4 cathode is 150 mW cm−2 at 800 °C
  Address
  Corporate Author Thesis
  Publisher Place of Publication Editor
  Language Wos 000387427700044 Publication Date 2016-10-19
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 2046-2069 ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 3.108 Times cited 7 Open Access
  Notes his work was partially supported by Russian Foundation for Basic Research (grant no. 153820247), Skolkovo Institute of Science and Technology (Center of electrochemical energy), and MSUdevelopment Program up to 2020. K.L.M. is grateful to Haldor Topsøe A/S for the financial support. Approved Most recent IF: 3.108
  Call Number EMAT @ emat @ c:irua:136441 Serial 4296
Permanent link to this record
 

 
Author Meert, K.W.; Morozov, V.A.; Abakumov, A.M.; Hadermann, J.; Poelman, D.; Smet, P.F.
  Title (down) Energy transfer in Eu3+ doped scheelites : use as thermographic phosphor Type A1 Journal article
  Year 2014 Publication Optics express Abbreviated Journal Opt Express
  Volume 22 Issue 9 Pages A961-A972
  Keywords A1 Journal article; Electron microscopy for materials research (EMAT)
  Abstract In this paper the luminescence of the scheelite-based CaGd2(1-x)Eu2x(WO4)4 solid solutions is investigated as a function of the Eu content and temperature. All phosphors show intense red luminescence due to the 5D0 7F2 transition in Eu3+, along with other transitions from the 5D1 and 5D0 excited states. For high Eu3+ concentrations the intensity ratio of the emission originating from the 5D1 and 5D0 levels has a non-conventional temperature dependence, which could be explained by a phonon-assisted cross-relaxation process. It is demonstrated that this intensity ratio can be used as a measure of temperature with high spatial resolution, allowing the use of these scheelites as thermographic phosphor. The main disadvantage of many thermographic phosphors, a decreasing signal for increasing temperature, is absent.
  Address
  Corporate Author Thesis
  Publisher Place of Publication Editor
  Language Wos 000335905300037 Publication Date 2014-04-22
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 1094-4087; ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 3.307 Times cited 47 Open Access
  Notes Approved Most recent IF: 3.307; 2014 IF: 3.488
  Call Number UA @ lucian @ c:irua:117067 Serial 1044
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Author Batuk, D.; Batuk, M.; Abakumov, A.M.; Tsirlin, A.A.; McCammon, C.M.; Dubrovinsky, L.; Hadermann, J.
  Title (down) Effect of lone-electron-pair cations on the orientation of crystallographic shear planes in anion-deficient perovskites Type A1 Journal article
  Year 2013 Publication Inorganic chemistry Abbreviated Journal Inorg Chem
  Volume 52 Issue 17 Pages 10009-10020
  Keywords A1 Journal article; Electron microscopy for materials research (EMAT)
  Abstract Factors affecting the structure and orientation of the crystallographic shear (CS) planes in anion-deficient perovskites are investigated using the (Pb1−zSrz)1−xFe1+xO3−y perovskites as a model system. The orientation of the CS planes in the system varies unevenly with z. A comparison of the structures with different CS planes revels that the orientation of the CS planes is governed mainly by the stereochemical activity of the lone-electron-pair cations inside the perovskite blocks.
  Address
  Corporate Author Thesis
  Publisher Place of Publication Easton, Pa Editor
  Language Wos 000326129000037 Publication Date 2013-08-22
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 0020-1669;1520-510X; ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 4.857 Times cited 11 Open Access
  Notes Fwo Approved Most recent IF: 4.857; 2013 IF: 4.794
  Call Number UA @ lucian @ c:irua:111394 Serial 822
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Author Batuk, D.; Batuk, M.; Morozov, V.A.; Meert, K.W.; Smet, P.F.; Poelman, D.; Abakumov, A.M.; Hadermann, J.
  Title (down) Effect of cation vacancies on the crystal structure and luminescent properties of Ca(0.85-1.5x)Gd(x)Eu(0.1)_(0.05+0.5x)WO(4) (0<x<0.567) scheelite-based red phosphors Type A1 Journal article
  Year 2017 Publication Journal of alloys and compounds Abbreviated Journal J Alloy Compd
  Volume 706 Issue 706 Pages 358-369
  Keywords A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
  Abstract The Ca0.85-1.5xGdxEu0.1_0.05-0.5xWO4 (0 < x < 0.567) series of cation-deficient scheelites is investigated to unveil the influence of the cation vacancies on the crystal structure and luminescent properties. The concentration of the vacancies is varied by the heterovalent substitution of Gd3+ for Ca2+, keeping the concentration of the Eu3+ luminescent centers constant in all compounds of the series. The crystal structure of the materials is studied using a combination of transmission electron microscopy and synchrotron X-ray powder diffraction. At low vacancy concentration (x = 0.1, 0.2), cations and cation vacancies are randomly distributed in the structure, and the materials preserve the I41/a symmetry of the parent scheelite structure [x = 0.1: a = 5.25151(1) Å, c = 11.39479(2) Å; x = 0.2: a = 5.25042(1) Å, c = 11.41335(2) Å]. At higher concentration, the cation-vacancy ordering gives rise to incommensurately modulated structures. The x = 0.3 structure has a (3 + 2)D tetragonal symmetry [superspace group I41/a(a,b,0)00(-b,a,0)00, a = 5.24700(1) Å, c = 11.45514(3) Å, q1 = 0.51637(14)a* + 0.80761(13)b*, q2 = -0.80761a* + 0.51637b*]. At x = 0.4, the scheelite basic cell undergoes a monoclinic distortion with the formation of the (3 + 1)D structure [superspace group I2/b(a,b,0)00, a = 5.23757(1) Å, b = 5.25035(1) Å, c = 11.45750(2) Å, g = 90.5120(2) o, q = 0.54206(8)a* + 0.79330(8)b*]. In both structures, the antiphase Ca and (Gd,Eu) occupancy modulations indicate that the ordering between the A cations and vacancies also induces partial Ca/(Gd,Eu) cation ordering. Further increase of the Gd3þ content up to x = 0.567 leads to the formation of a monoclinic phase (space group C2/c) with the Eu2/3WO4-type structure. Despite the difference in the cation-vacancy ordering patterns, all materials in the series demonstrate very similar quantum efficiency and luminescence decay lifetimes. However, the difference in the local coordination environment of the A cation species noticeably affects the line width and the multiplet splitting of the 4f6-4f6 transitions.
  Address
  Corporate Author Thesis
  Publisher Place of Publication Editor
  Language Wos 000397997300045 Publication Date 2017-02-16
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 0925-8388 ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 3.133 Times cited 2 Open Access OpenAccess
  Notes This research was supported by FWO (Flanders Research Foundation, project G039211N). V.A.M. is grateful for financial support of the Russian Foundation for Basic Research (Grant 15-03-07741).We are grateful to the ESRF for granting the beamtime at the ID22 beamline and to Andy Fitch for the support during the experiment. Approved Most recent IF: 3.133
  Call Number EMAT @ emat @ c:irua:142367 Serial 4581
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Author Rozova, M.G.; Grigoriev, V.V.; Tyablikov, O.A.; Filimonov, D.S.; Zakharov, K.V.; Volkova, O.S.; Vasiliev, A.N.; Antipov, E.V.; Abakumov, A.M.
  Title (down) Doping of Bi4Fe5O13F with pentagonal Cairo lattice with Cr and Mn: Synthesis, structure and magnetic properties Type A1 Journal article
  Year 2017 Publication Materials research bulletin Abbreviated Journal Mater Res Bull
  Volume 87 Issue 87 Pages 54-60
  Keywords A1 Journal article; Electron microscopy for materials research (EMAT)
  Abstract The substitution of Cr3+ and Mn3+ for Fe3+ in the Bi4Fe6O13F oxyfluoride featuring the magnetically frustrated pentagonal Cairo lattice is reported. Bi4Fe4.1Cr0.9O13F and BiFe4.2Mn0.8O13F have been prepared using a solid state reaction in inert atmosphere. Their crystal structures were studied with transmission electron microscopy, powder X-ray diffraction and Fe-57 Mossbauer spectroscopy (S.G. P4(2)/mbc, a = 8.27836(2)angstrom, c = 18.00330(9) angstrom, R-F = 0.031 (Bi4Fe4.1Cr0.9O13F)), a= 8.29535(3)angstrom, c= 18.0060(1)angstrom, R-F = 0.027 (Bi4Fe4.1Cr0.9O13F)). The structures are formed by infinite rutile-like chains of the edge sharing BO6 octahedra (B transition metal cations) linked by the Fe2O7 groups of two corner-sharing tetrahedra. The"voids in thus formed framework are occupied by the Bi4F tetrahedra. The Fe-57 Mossbauer spectroscopy reveals that Cr3+ and Mn3+ replace Fe3+. exclusively at the octahedral positions. The Mn- and Cr-doped compounds demonstrate antiferromagnetic ordering below T-N =165 K and 120 K, respectively. (C) 2016 Elsevier Ltd. All rights reserved.
  Address
  Corporate Author Thesis
  Publisher Place of Publication New York, N.Y. Editor
  Language Wos 000392681800009 Publication Date 2016-11-17
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 0025-5408 ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 2.446 Times cited 1 Open Access Not_Open_Access
  Notes ; The work has been supported by the Russian Science Foundation (grant 14-13-00680). ; Approved Most recent IF: 2.446
  Call Number UA @ lucian @ c:irua:141535 Serial 4498
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Author Gou, H.; Dubrovinskaia, N.; Bykova, E.; Tsirlin, A.A.; Kasinathan, D.; Schnelle, W.; Richter, A.; Merlini, M.; Hanfland, M.; Abakumov, A.M.; Batuk, D.; Van Tendeloo, G.; Nakajima, Y.; Kolmogorov, A.N.; Dubrovinsky, L.;
  Title (down) Discovery of a superhard iron tetraboride superconductor Type A1 Journal article
  Year 2013 Publication Physical review letters Abbreviated Journal Phys Rev Lett
  Volume 111 Issue 15 Pages 157002-157005
  Keywords A1 Journal article; Electron microscopy for materials research (EMAT)
  Abstract Single crystals of novel orthorhombic (space group Pnnm) iron tetraboride FeB4 were synthesized at pressures above 8 GPa and high temperatures. Magnetic susceptibility and heat capacity measurements demonstrate bulk superconductivity below 2.9 K. The putative isotope effect on the superconducting critical temperature and the analysis of specific heat data indicate that the superconductivity in FeB4 is likely phonon mediated, which is rare for Fe-based superconductors. The discovered iron tetraboride is highly incompressible and has the nanoindentation hardness of 62(5) GPa; thus, it opens a new class of highly desirable materials combining advanced mechanical properties and superconductivity.
  Address
  Corporate Author Thesis
  Publisher Place of Publication New York, N.Y. Editor
  Language Wos 000325371500011 Publication Date 2013-10-09
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 0031-9007;1079-7114; ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 8.462 Times cited 127 Open Access
  Notes Countatoms Approved Most recent IF: 8.462; 2013 IF: 7.728
  Call Number UA @ lucian @ c:irua:110820 Serial 729
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Author Hadermann, J.; Abakumov, A.M.; Tsirlin, A.A.; Filonenko, V.P.; Gonnissen, J.; Tan, H.; Verbeeck, J.; Gemmi, M.; Antipov, E.V.; Rosner, H.
  Title (down) Direct space structure solution from precession electron diffraction data: resolving heavy and light scatterers in Pb13Mn9O25 Type A1 Journal article
  Year 2010 Publication Ultramicroscopy Abbreviated Journal Ultramicroscopy
  Volume 110 Issue 7 Pages 881-890
  Keywords A1 Journal article; Electron microscopy for materials research (EMAT)
  Abstract The crystal structure of a novel compound Pb13Mn9O25 has been determined through a direct space structure solution with a Monte-Carlo-based global optimization using precession electron diffraction data (a=14.177(3) Å, c=3.9320(7) Å, SG P4/m, RF=0.239) and compositional information obtained from energy dispersive X-ray analysis and electron energy loss spectroscopy. This allowed to obtain a reliable structural model even despite the simultaneous presence of both heavy (Pb) and light (O) scattering elements and to validate the accuracy of the electron diffraction-based structure refinement. This provides an important benchmark for further studies of complex structural problems with electron diffraction techniques. Pb13Mn9O25 has an anion- and cation-deficient perovskite-based structure with the A-positions filled by the Pb atoms and 9/13 of the B positions filled by the Mn atoms in an ordered manner. MnO6 octahedra and MnO5 tetragonal pyramids form a network by sharing common corners. Tunnels are formed in the network due to an ordered arrangement of vacancies at the B-sublattice. These tunnels provide sufficient space for localization of the lone 6s2 electron pairs of the Pb2+ cations, suggested as the driving force for the structural difference between Pb13Mn9O25 and the manganites of alkali-earth elements with similar compositions.
  Address
  Corporate Author Thesis
  Publisher Place of Publication Amsterdam Editor
  Language Wos 000280050900023 Publication Date 2010-04-01
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 0304-3991; ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 2.843 Times cited 24 Open Access
  Notes Fwo; Bof; Esteem Approved Most recent IF: 2.843; 2010 IF: 2.063
  Call Number UA @ lucian @ c:irua:84085UA @ admin @ c:irua:84085 Serial 721
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Author Altantzis, T.; Coutino-Gonzalez, E.; Baekelant, W.; Martinez, G.T.; Abakumov, A.M.; Van Tendeloo, G.; Roeffaers, M.B.J.; Bals, S.; Hofkens, J.
  Title (down) Direct Observation of Luminescent Silver Clusters Confined in Faujasite Zeolites Type A1 Journal article
  Year 2016 Publication ACS nano Abbreviated Journal Acs Nano
  Volume 10 Issue 10 Pages 7604-7611
  Keywords A1 Journal article; Electron microscopy for materials research (EMAT)
  Abstract One of the ultimate goals in the study of metal clusters is the correlation between the atomic-scale organization and their physicochemical properties. However, direct observation of the atomic organization of such minuscule metal clusters is heavily hindered by radiation damage imposed by the different characterization techniques. We present direct evidence of the structural arrangement, at an atomic level, of luminescent silver species stabilized in faujasite (FAU) zeolites using aberration-corrected scanning transmission electron microscopy. Two different silver clusters were identified in Ag-FAU zeolites, a trinuclear silver species associated with green emission and a tetranuclear silver species related to yellow emission. By combining direct imaging with complementary information obtained from X-ray powder diffraction and Rietveld analysis, we were able to elucidate the main differences at an atomic scale between luminescent (heat-treated) and nonluminescent (cation-exchanged) Ag-FAU zeolites. It is expected that such insights will trigger the directed synthesis of functional metal nanocluster-zeolite composites with tailored luminescent properties.
  Address RIES, Hokkaido University , N20W10, Kita-Ward Sapporo 001-0020, Japan
  Corporate Author Thesis
  Publisher Place of Publication Editor
  Language English Wos 000381959100043 Publication Date 2016-07-08
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 1936-0851 ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 13.942 Times cited 57 Open Access OpenAccess
  Notes The authors gratefully acknowledge financial support from the Belgian Federal government (Belspo through the IAP-VI/27 and IAP-VII/05 programs), the European Union’s Seventh Framework Programme (FP7/2007-2013 under grant agreement no. 310651 SACS and no. 312483-ESTEEM2), the Flemish government in the form of long-term structural funding “Methusalem” grant METH/15/04 CASAS2, the Hercules foundation (HER/11/14), the “Strategisch Initiatief Materialen” SoPPoM program, and the Fund for Scientific Research Flanders (FWO) grants G.0349.12 and G.0B39.15. S.B. acknowledges funding from ERC Starting Grant COLOURATOMS (335078). The authors thank Prof. S. Van Aert for helpful discussions, Dr. T. De Baerdemaeker for XRD measurements, Mr. B. Dieu for the preparation of graphical material, and UOP Antwerp for the kind donation of zeolite samples.; esteem2jra4; ECASSara; (ROMEO:white; preprint:; postprint:restricted 12 months embargo; pdfversion:cannot); Approved Most recent IF: 13.942
  Call Number c:irua:134576 c:irua:134576 Serial 4102
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Author Gonnissen, J.; Batuk, D.; Nataf, G.F.; Jones, L.; Abakumov, A.M.; Van Aert, S.; Schryvers, D.; Salje, E.K.H.
  Title (down) Direct Observation of Ferroelectric Domain Walls in LiNbO3: Wall-Meanders, Kinks, and Local Electric Charges Type A1 Journal article
  Year 2016 Publication Advanced functional materials Abbreviated Journal Adv Funct Mater
  Volume 26 Issue 26 Pages 7599-7604
  Keywords A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
  Abstract Direct observations of the ferroelectric domain boundaries in LiNbO3 are performed using high-resolution high-angle annular dark field scanning transmission electron microscopy imaging, revealing a very narrow width of the domain wall between the 180° domains. The domain walls demonstrate local side-way meandering, which results in inclinations even when the overall wall orientation follows the ferroelectric polarization. These local meanders contain kinks with “head-to-head” and “tail-to-tail” dipolar configurations and are therefore locally charged. The charged meanders are confined to a few cation layers along the polarization direction and are separated by longer stretches of straight domain walls.
  Address
  Corporate Author Thesis
  Publisher Place of Publication Editor
  Language Wos 000388166700006 Publication Date 2016-09-16
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 1616-301X ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 12.124 Times cited 23 Open Access
  Notes J.G. acknowledges the support from the Research Foundation Flanders (FWO, Belgium) through various project fundings (G.0368.15N, G.0369.15N, and G.0374.13N), as well as the financial support from the European Union Seventh Framework Program (FP7/2007–2013) under Grant agreement no. 312483 (ESTEEM2). The authors thank J. Hadermann for useful suggestions on the interpretation of the HAADFSTEM images. E.K.H.S. thanks the EPSRC (EP/K009702/1) and the Leverhulme Trust (EM-2016-004) for support. G.F.N. thanks the National Research Fund, Luxembourg (FNR/P12/4853155/Kreisel) for support.; esteem2_jra2 Approved Most recent IF: 12.124
  Call Number c:irua:135336 c:irua:135336 Serial 4129
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Author Rossell, M.D.; Abakumov, A.M.; Ramasse, Q.M.; Erni, R.
  Title (down) Direct evidence of stacking disorder in the mixed ionic-electronic conductor Sr4Fe6O12+\delta Type A1 Journal article
  Year 2013 Publication ACS nano Abbreviated Journal Acs Nano
  Volume 7 Issue 4 Pages 3078-3085
  Keywords A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
  Abstract Determining the structure-to-property relationship of materials becomes particularly challenging when the material under investigation is dominated by defects and structural disorder. Knowledge on the exact atomic arrangement at the defective structure is required to understand its influence on the functional properties. However, standard diffraction techniques deliver structural information that is averaged over many unit cells. In particular, information about defects and order-disorder phenomena is contained in the coherent diffuse scattering intensity which often is difficult to uniquely interpret. Thus, the examination of the local disorder in materials requires a direct method to study their structure on the atomic level with chemical sensitivity. Using aberration-corrected scanning transmission electron microscopy in combination with atomic-resolution electron energy-loss spectroscopy, we show that the controversial structural arrangement of the Fe2O2+delta layers in the mixed ionic-electronic conducting Sr4Fe6O12+delta perovskite can be unambiguously resolved. Our results provide direct experimental evidence for the presence of a nanomixture of “ordered” and “disordered” domains in an epitaxial Sr4Fe6O12+delta thin film. The most favorable arrangement is the disordered structure and is interpreted as a randomly occurring but well-defined local shift of the Fe-O chains in the Fe2O2+delta layers. By analyzing the electron energy-loss near-edge structure of the different building blocks in the Sr4Fe6O12+delta unit cell we find that the mobile holes in this mixed ionic-electronic conducting oxide are highly localized in the Fe2O2+delta layers, which are responsible for the oxide-ion conductivity. A possible link between disorder and oxygen-ion transport along the Fe2O2+delta layers is proposed by arguing that the disorder can effectively break the oxygen diffusion pathways.
  Address
  Corporate Author Thesis
  Publisher Place of Publication Editor
  Language Wos 000318143300021 Publication Date 2013-03-04
  Series Editor Series Title Abbreviated Series Title
  Series Volume Series Issue Edition
  ISSN 1936-0851;1936-086X; ISBN Additional Links UA library record; WoS full record; WoS citing articles
  Impact Factor 13.942 Times cited 4 Open Access
  Notes Approved Most recent IF: 13.942; 2013 IF: 12.033
  Call Number UA @ lucian @ c:irua:108476 Serial 713
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