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“Direct evidence of stacking disorder in the mixed ionic-electronic conductor Sr4Fe6O12+\delta”. Rossell MD, Abakumov AM, Ramasse QM, Erni R, ACS nano 7, 3078 (2013). http://doi.org/10.1021/nn3058449
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.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 13.942
Times cited: 4
DOI: 10.1021/nn3058449
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“Ca6.3Mn3Ga4.4Al1.3O18: a novel complex oxide with 3D tetrahedral framework”. Abakumov AM, Hadermann J, Kalyuzhnaya AS, Rozova MG, Mikheev MG, Van Tendeloo G, Antipov EV, Journal of solid state chemistry 178, 3137 (2005). http://doi.org/10.1016/j.jssc.2005.07.028
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.299
Times cited: 5
DOI: 10.1016/j.jssc.2005.07.028
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“Pb2.85Ba2.15Fe4SnO13 : a new member of the AnBnO3n-2 anion-deficient perovskite-based homologous series”. Korneychik OE, Batuk M, Abakumov AM, Hadermann J, Rozova MG, Sheptyakov DV, Pokholok KV, Filimonov DS, Antipov EV, Journal of solid state chemistry 184, 3150 (2011). http://doi.org/10.1016/j.jssc.2011.09.029
Abstract: Pb2.85Ba2.15Fe4SnO13, a new n=5 member of the anion-deficient perovskite based AnBnO3n−2 (A=Pb, Ba, B=Fe, Sn) homologous series, was synthesized by the solid state method. The crystal structure of Pb2.85Ba2.15Fe4SnO13 was investigated using a combination of neutron powder diffraction, electron diffraction, high angle annular dark field scanning transmission electron microscopy and Mössbauer spectroscopy. It crystallizes in the Ammm space group with unit cell parameters a=5.7990(1) Å, b=4.04293(7) Å and c=26.9561(5) Å. The Pb2.85Ba2.15Fe4SnO13 structure consists of quasi two-dimensional perovskite blocks separated by 1/2[110](1̄01)p crystallographic shear (CS) planes. The corner-sharing FeO6 octahedra at the CS planes are transformed into edge-sharing FeO5 distorted tetragonal pyramids. The octahedral positions in the perovskite blocks between the CS planes are jointly taken up by Fe and Sn, with a preference of Sn towards the position at the center of the perovskite block. The chains of FeO5 pyramids and (Fe,Sn)O6 octahedra of the perovskite blocks delimit six-sided tunnels at the CS planes occupied by double chains of Pb atoms. The compound is antiferromagnetically ordered below TN=368±15 K.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.299
Times cited: 7
DOI: 10.1016/j.jssc.2011.09.029
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“Topochemical nitridation with anion vacancy -assisted N3-/O2- exchange”. Mikita R, Aharen T, Yamamoto T, Takeiri F, Ya T, Yoshimune W, Fujita K, Yoshida S, Tanaka K, Batuk D, Abakumov AM, Brown CM, Kobayashi Y, Kageyama H;, Journal of the American Chemical Society 138, 3211 (2016). http://doi.org/10.1021/jacs.6b00088
Abstract: We present how the introduction of anion vacancies in oxyhydrides enables a route to access new oxynitrides, by conducting ammonolysis of perovskite oxyhydride EuTiO3-xHx (x similar to 0.18). At 400 degrees C, similar to our studies on BaTiO3-xHx, hydride lability enables a low temperature direct ammonolysis of EUTi3.82+O-2.82/H-0.18, leading to the N3-/H--exchanged product EuTi4+O2.82No0.12 square 0.06 center dot When the ammonolysis temperature was increased up to 800 degrees C, we observed a further nitridation involving N3-/O2- exchange, yielding a fully oxidized Eu3+Ti4+O2N with the GdFeO3-type distortion (Pnma) as a metastable phase, instead of pyrochlore structure. Interestingly, the same reactions using the oxide EuTiO3 proceeded through a 1:1 exchange of N3- with O-2 only above 600 degrees C and resulted in incomplete nitridation to EuTi02.25N0.75, indicating that anion vacancies created during the initial nitridation process of EuTiO2.82H0.18 play a crucial role in promoting anion (N3-/O2-) exchange at high temperatures. Hence, by using (hydride-induced) anion-deficient precursors, we should be able to expand the accessible anion composition of perovskite oxynitrides.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 13.858
Times cited: 28
DOI: 10.1021/jacs.6b00088
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“β-Na1.7IrO3: A Tridimensional Na-Ion Insertion Material with a Redox Active Oxygen Network”. Pearce PE, Rousse G, Karakulina OM, Hadermann J, Van Tendeloo G, Foix D, Fauth F, Abakumov AM, Tarascon J-M, Chemistry of materials 30, 3285 (2018). http://doi.org/10.1021/acs.chemmater.8b00320
Abstract: The revival of the Na-ion battery concept has prompted an intense search for new high capacity Na-based positive electrodes. Recently, emphasis has been placed on manipulating Na-based layered compounds to trigger the participation of the anionic network. We further explored this direction and show the feasibility of achieving anionic-redox activity in three-dimensional Na-based compounds. A new 3D β-Na1.7IrO3 phase was synthesized in a two-step process, which involves first the electrochemical removal of Li from β-Li2IrO3 to produce β-IrO3, which is subsequently reduced by electrochemical Na insertion. We show that β-Na1.7IrO3 can reversibly uptake nearly 1.3 Na+ per formula unit through an uneven voltage profile characterized by the presence of four plateaus related to structural transitions. Surprisingly, the β-Na1.7IrO3 phase was found to be stable up to 600 °C, while it could not be directly synthesized via conventional synthetic methods. Although these Na-based iridate phases are of limited practical interest, they help to understand how introducing highly polarizable guest ions (Na+) into host rocksalt-derived oxide structures affects the anionic redox mechanism.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 6
DOI: 10.1021/acs.chemmater.8b00320
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“Multiple twinning as a structure directing mechanism in layered rock-salt-type oxides : NaMnO2 polymorphism, redox potentials, and magnetism”. Abakumov AM, Tsirlin AA, Bakaimi I, Van Tendeloo G, Lappas A, Chemistry of materials 26, 3306 (2014). http://doi.org/10.1021/cm5011696
Abstract: New polymorphs of NaMnO2 have been observed using transmission electron microscopy and synchrotron X-ray powder diffraction. Coherent twin planes confined to the (NaMnO2) layers, parallel to the (10 (1) over bar) crystallographic planes of the monoclinic layered rock-salt-type alpha-NaMnO2 (O3) structure, form quasi-periodic modulated sequences, with the known alpha-and beta-NaMnO2 polymorphs as the two limiting cases. The energy difference between the polymorphic forms, estimated using a DFT-based structure relaxation, is on the scale of the typical thermal energies that results in a high degree of stacking disorder in these compounds. The results unveil the remarkable effect of the twin planes on both the magnetic and electrochemical properties. The polymorphism drives the magnetic ground state from a quasi-1D spin system for the geometrically frustrated alpha-polymorph through a two-leg spin ladder for the intermediate stacking sequence toward a quasi-2D magnet for the beta-polymorph. A substantial increase of the equilibrium potential for Na deintercalation upon increasing the concentration of the twin planes is calculated, providing a possibility to tune the electrochemical potential of the layered rock-salt ABO(2) cathodes by engineering the materials with a controlled concentration of twins.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 35
DOI: 10.1021/cm5011696
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“Decoupling the roles of carbon and metal oxides on the electrocatalytic reduction of oxygen on La1-xSrxCoO3-\delta perovskite composite electrodes”. Mefford JT, Kurilovich AA, Saunders J, Hardin WG, Abakumov AM, Forslund RP, Bonnefont A, Dai S, Johnston KP, Stevenson KJ, Physical chemistry, chemical physics 21, 3327 (2019). http://doi.org/10.1039/C8CP06268D
Abstract: Perovskite oxides are active room-temperature bifunctional oxygen electrocatalysts in alkaline media, capable of performing the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with lower combined overpotentials relative to their precious metal counterparts. However, their semiconducting nature necessitates the use of activated carbons as conductive supports to generate applicably relevant current densities. In efforts to advance the performance and theory of oxide electrocatalysts, the chemical and physical properties of the oxide material often take precedence over contributions from the conductive additive. In this work, we find that carbon plays an important synergistic role in improving the performance of La1-xSrxCoO3- (0 x 1) electrocatalysts through the activation of O-2 and spillover of radical oxygen intermediates, HO2- and O-2(-), which is further reduced through chemical decomposition of HO2- on the perovskite surface. Through a combination of thin-film rotating disk electrochemical characterization of the hydrogen peroxide intermediate reactions (hydrogen peroxide reduction reaction (HPRR), hydrogen peroxide oxidation reaction (HPOR)) and oxygen reduction reaction (ORR), surface chemical analysis, HR-TEM, and microkinetic modeling on La1-xSrxCoO3- (0 x 1)/carbon (with nitrogen and non-nitrogen doped carbons) composite electrocatalysts, we deconvolute the mechanistic aspects and contributions to reactivity of the oxide and carbon support.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.123
Times cited: 5
DOI: 10.1039/C8CP06268D
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“Crystal structure of a lightweight borohydride from submicrometer crystallites by precession electron diffraction”. Hadermann J, Abakumov A, Van Rompaey S, Perkisas T, Filinchuk Y, Van Tendeloo G, Chemistry of materials 24, 3401 (2012). http://doi.org/10.1021/cm301548k
Abstract: We demonstrate that precession electron diffraction at low-dose conditions can be successfully applied for structure analysis of extremely electron-beam-sensitive materials. Using LiBH4 as a test material, complete structural information, including the location of the H atoms, was obtained from submicrometer-sized crystallites. This demonstrates for the first time that, where conventional transmission electron microscopy techniques fail, quantitative precession electron diffraction can provide structural information from submicrometer particles of such extremely electron-beam-sensitive materials as complex lightweight hydrides. We expect the precession electron diffraction technique to be a useful tool for nanoscale investigations of thermally unstable lightweight hydrogen-storage materials.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 17
DOI: 10.1021/cm301548k
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“Structure and magnetic properties of a new anion-deficient perovskite Pb2Ba2BiFe4ScO13 with crystallographic shear structure”. Batuk M, Tyablikov OA, Tsirlin AA, Kazakov SM, Rozova MG, Pokholok KV, Filimonov DS, Antipov EV, Abakumov AM, Hadermann J, Materials research bulletin 48, 3459 (2013). http://doi.org/10.1016/j.materresbull.2013.05.028
Abstract: Pb2Ba2BiFe4ScO13, a new n = 5 member of the oxygen-deficient perovskite-based A(n)B(n)O(3n-2) homologous series, was synthesized using a solid-state method. The crystal structure of Pb2Ba2BiFe4ScO13 was investigated by a combination of synchrotron X-ray powder diffraction, electron diffraction, high-angle annular dark-field scanning transmission electron microscopy and Mossbauer spectroscopy. At 900 K, it crystallizes in the Ammm space group with the unit cell parameters a = 5.8459(1) angstrom, b = 4.0426(1) angstrom, and c=27.3435(1) angstrom. In the Pb2Ba2BiFe4ScO13 structure, quasi-two-dimensional perovskite blocks are periodically interleaved with 1/2[1 1 0] ((1) over bar 0 1)(p) crystallographic shear (CS) planes. At the CS planes, the corner-sharing FeO6 octahedra are transformed into chains of edge-sharing FeO5 distorted tetragonal pyramids. B-positions of the perovskite blocks between the CS planes are jointly occupied by Fe3+ and Sc3+. The chains of the FeO5 pyramids and (Fe,Sc)O-6 octahedra delimit six-sided tunnels that are occupied by double columns of cations with a lone electron pair (Pb2+). The remaining A-cations (Bi3+, Ba2+) occupy positions in the perovskite block. According to the magnetic susceptibility measurements, Pb2Ba2BiFe4ScO13 is antiferromagnetically ordered below T-N approximate to 350 K. (C) 2013 Elsevier Ltd. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.446
Times cited: 2
DOI: 10.1016/j.materresbull.2013.05.028
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“Solving the structure of Li ion battery materials with precession electron diffraction : application to Li2CoPo4F”. Hadermann J, Abakumov AM, Turner S, Hafideddine Z, Khasanova NR, Antipov EV, Van Tendeloo G, Chemistry of materials 23, 3540 (2011). http://doi.org/10.1021/cm201257b
Abstract: The crystal structure of the Li2CoPO4F high-voltage cathode for Li ion rechargeable batteries has been completely solved from precession electron diffraction (PED) data, including the location of the Li atoms. The crystal structure consists of infinite chains of CoO4F2 octahedra sharing common edges and linked into a 3D framework by PO4 tetrahedra. The chains and phosphate anions together delimit tunnels filled with the Li atoms. This investigation demonstrates that PED can be successfully applied for obtaining structural information on a variety of Li-containing electrode materials even from single micrometer-sized crystallites.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 46
DOI: 10.1021/cm201257b
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“Cs7Nd11(SeO3)12Cl16 : first noncentrosymmetric structure among alkaline-metal lanthanide selenite halides”. Berdonosov PS, Akselrud L, Prots Y, Abakumov AM, Smet PF, Poelman D, Van Tendeloo G, Dolgikh VA, Inorganic chemistry 52, 3611 (2013). http://doi.org/10.1021/ic301442f
Abstract: Cs7Nd11(SeO3)(12)Cl-16, the complex selenite chloride of cesium and neodymium, was synthesized in the NdOCl-SeO2-CsCl system. The compound has been characterized using single-crystal X-ray diffraction, electron diffraction, transmission electron microscopy, luminescence spectroscopy, and second-harmonic-generation techniques. Cs7Nd11(SeO3)(12)Cl-16 crystallizes in an orthorhombic unit cell with a = 15.911(1) angstrom, b = 15.951(1) angstrom, and c = 25.860(1) angstrom and a noncentrosymmetric space group Pna2(1) (No. 33). The crystal structure of Cs7Nd11(SeO3)(12)Cl-16 can be represented as a stacking of Cs7Nd11(SeO3)(12) lamellas and CsCl-like layers. Because of the layered nature of the Cs7Nd11(SeO3)(12)Cl-16 structure, it features numerous planar defects originating from occasionally missing the CsCl-like layer and violating the perfect stacking of the Cs7Nd11(SeO3)(12)Cl-16 lamellas. Cs7Nd11(SeO3)(12)Cl-16 represents the first example of a noncentrosymmetric structure among alkaline-metal lanthanide selenite halides. Cs7Nd11(SeO3)(12)Cl-16 demonstrates luminescence emission in the near-IR region with reduced efficiency due to a high concentration of Nd3+ ions causing nonradiative cross-relaxation.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.857
Times cited: 10
DOI: 10.1021/ic301442f
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“Preparation, structure, and electrochemistry of layered polyanionic hydroxysulfates : LiMSO4OH (M = Fe, Co, Mn) electrodes for Li-Ion batteries”. Subban CV, Ati M, Rousse G, Abakumov AM, Van Tendeloo G, Janot R, Tarascon J-M, Journal of the American Chemical Society 135, 3653 (2013). http://doi.org/10.1021/ja3125492
Abstract: The Li-ion rechargeable battery, due to its high energy density, has driven remarkable advances in portable electronics. Moving toward more sustainable electrodes could make this technology even more attractive to large-volume applications. We present here a new family of 3d-metal hydroxysulfates of general formula LiMSO4OH (M = Fe, Co, and Mn) among which (i) LiFeSO4OH reversibly releases 0.7 Li+ at an average potential of 3.6 V vs Li+/Li-0, slightly higher than the potential of currently lauded LiFePO4 (3.45 V) electrode material, and (ii) LiCoSO4OH shows a redox activity at 4.7 V vs Li+/Li-0. Besides, these compounds can be easily made at temperatures near 200 degrees C via a synthesis process that enlists a new intermediate phase of composition M-3(SO4)(2)(OH)(2) (M = Fe, Co, Mn, and Ni), related to the mineral caminite. Structurally, we found that LiFeSO4OH is a layered phase unlike the previously reported 3.2 V tavorite LiFeSO4OH. This work should provide an impetus to experimentalists for designing better electrolytes to fully tap the capacity of high-voltage Co-based hydroxysulfates, and to theorists for providing a means to predict the electrochemical redox activity of two polymorphs.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 13.858
Times cited: 53
DOI: 10.1021/ja3125492
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“A polar corundum oxide displaying weak ferromagnetism at room temperature”. Li MR, Adem U, McMitchell SRC, Xu Z, Thomas CI, Warren JE, Giap DV, Niu H, Wan X, Palgrave RG, Schiffmann F, Cora F, Slater B, Burnett TL, Cain MG, Abakumov AM, Van Tendeloo G, Thomas MF, Rosseinsky MJ, Claridge JB;, Journal of the American Chemical Society 134, 3737 (2012). http://doi.org/10.1021/ja208395z
Abstract: Combining long-range magnetic order with polarity in the same structure is a prerequisite for the design of (magnetoelectric) multiferroic materials. There are now several demonstrated strategies to achieve this goal, but retaining magnetic order above room temperature remains a difficult target. Iron oxides in the +3 oxidation state have high magnetic ordering temperatures due to the size of the coupled moments. Here we prepare and characterize ScFeO3 (SFO), which under pressure and in strain-stabilized thin films adopts a polar variant of the corundum structure, one of the archetypal binary oxide structures. Polar corundum ScFeO3 has a weak ferromagnetic ground state below 356 K-this is in contrast to the purely antiferromagnetic ground state adopted by the well-studied ferroelectric BiFeO3.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 13.858
Times cited: 48
DOI: 10.1021/ja208395z
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“Chemical activity of the peroxide/oxide redox couple : case study of Ba5Ru2O11 in aqueous and organic solvents”. Grimaud A, Iadecola A, Batuk D, Saubanere M, Abakumov AM, Freeland JW, Cabana J, Li H, Doublet M-L, Rousse G, Tarascon J-M, Chemistry of materials 30, 3882 (2018). http://doi.org/10.1021/ACS.CHEMMATER.8B01372
Abstract: The finding that triggering the redox activity of oxygen ions within the lattice of transition metal oxides can boost the performances of materials used in energy storage and conversion devices such as Li-ion batteries or oxygen evolution electrocatalysts has recently spurred intensive and innovative research in the field of energy. While experimental and theoretical efforts have been critical in understanding the role of oxygen nonbonding states in the redox activity of oxygen ions, a clear picture of the redox chemistry of the oxygen species formed upon this oxidation process is still missing. This can be, in part, explained by the complexity in stabilizing and studying these species once electrochemically formed. In this work, we alleviate this difficulty by studying the phase Ba5Ru2O11, which contains peroxide O-2(2-) groups, as oxygen evolution reaction electrocatalyst and Li-ion battery material. Combining physical characterization and electrochemical measurements, we demonstrate that peroxide groups can easily be oxidized at relatively low potential, leading to the formation of gaseous dioxygen and to the instability of the oxide. Furthermore, we demonstrate that, owing to the stabilization at high energy of peroxide, the high-lying energy of the empty sigma* antibonding O-O states limits the reversibility of the electrochemical reactions when the O-2(2-)/O2- redox couple is used as redox center for Li-ion battery materials or as OER redox active sites. Overall, this work suggests that the formation of true peroxide O-2(2-) states are detrimental for transition metal oxides used as OER catalysts and Li-ion battery materials. Rather, oxygen species with O-O bond order lower than 1 would be preferred for these applications.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 2
DOI: 10.1021/ACS.CHEMMATER.8B01372
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“Competition between the Ni and Fe redox in the O3-NaNi1/3Fe1/3Mn1/3O2 cathode material for Na-ion batteries”. Shevchenko VA, Glazkova IS, Novichkov DA, Skvortsova I, V Sobolev A, Abakumov AM, Presniakov IA, Drozhzhin OA, V Antipov E, Chemistry of materials 35, 4015 (2023). http://doi.org/10.1021/ACS.CHEMMATER.3C00338
Abstract: Sodium-ion batteries are attracting great attention due to their low cost and abundance of sodium. The O3-type NaNi1/3Fe1/3Mn1/3O2 layered oxide material is a promising candidate for positive electrodes (cathodes) in Na-ion batteries. However, its stable electrochemical performance is restricted by the upper voltage limit of 4.0 V (vs Na/Na+), which allows for reversibly removing 0.5-0.55 Na+ per formula unit, corresponding to the capacity of 120-130 mAh.g(-1). Further reduction of sodium content inevitably accelerates capacity degradation, and this issue calls for a detailed study of the redox reactions that accompany the electrochemical (de)intercalation of a large amount of sodium. Here, we present operando and ex situ studies using powder X-ray diffraction and X-ray absorption spectroscopy combined with Fe-57 Mossbauer spectroscopy. Our approach reveals the sequence of the redox transitions that occur during the charge and discharge of O3-NaNi1/3Fe1/3Mn1/3O2. Our data show that in addition to nickel and iron cations oxidizing to M+4, a part of iron transforms into the “3 + delta” state owing to the fast electron exchange Fe3+ + Fe4+ <-> Fe4+ + Fe3+. This process freezes upon cooling the material to 35 K, producing Fe4+ cations, some of which occupy tetrahedral positions.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 8.6
DOI: 10.1021/ACS.CHEMMATER.3C00338
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“Uniform patterns of Fe-vacancy ordering in the Kx(Fe,Co)2-ySe2 superconductors”. Kazakov SM, Abakumov AM, Perz-Mato JM, Ovchinnikov AV, Roslova MV, Boltalin AI, Morozov IV, Antipov EV, Van Tendeloo G, Chemistry of materials 23, 4311 (2011). http://doi.org/10.1021/cm201203h
Abstract: The Fe-vacancy ordering patterns in the superconducting KxFe2ySe2 and nonsuperconducting Kx(Fe,Co)2ySe2 samples have been investigated by electron diffraction and high angle annular dark field scanning transmission electron microscopy. The Fe-vacancy ordering occurs in the ab plane of the parent ThCr2Si2-type structure, demonstrating two types of patterns. Superstructure I retains the tetragonal symmetry and can be described with the aI = bI = as√5 (as is the unit cell parameter of the parent ThCr2Si2-type structure) supercell and I4/m space group. Superstructure II reduces the symmetry to orthorhombic with the aII = as√2, bII = 2as√2 supercell and the Ibam space group. This type of superstructure is observed for the first time in KxFe2ySe2. The Fe-vacancy ordering is inhomogeneous: the disordered areas interleave with the superstructures I and II in the same crystallite. The observed superstructures represent the compositionally dependent uniform ordering patterns of two species (the Fe atoms and vacancies) on a square lattice. More complex uniform ordered configurations, including compositional stripes, can be predicted for different chemical compositions of the KxFe2ySe2 (0 < y < 0.5) solid solutions.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 20
DOI: 10.1021/cm201203h
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“Pb2MnTeO6 double perovskite : an antipolar anti-ferromagnet”. Retuerto M, Skiadopoulou S, Li MR, Abakumov AM, Croft M, Ignatov A, Sarkar T, Abbett BM, Pokorný, J, Savinov M, Nuzhnyy D, Prokleška J, Abeykoon M, Stephens PW, Hodges JP, Vaněk P, Fennie CJ, Rabe KM, Kamba S, Greenblatt M;, Inorganic chemistry 55, 4320 (2016). http://doi.org/10.1021/acs.inorgchem.6b00054
Abstract: Pb2MnTeO6, a new double perovskite, was synthesized. Its crystal structure was determined by synchrotron X-ray and powder neutron diffraction. Pb2MnTeO6 is monoclinic (I2/m) at room temperature with a regular arrangement of all the cations in their polyhedra. However, when the temperature is lowered to similar to 120 K it undergoes a phase transition from I2/m to C2/c structure. This transition is accompanied by a displacement of the Pb atoms from the center of their polyhedra due to the 6s2 lone-pair electrons, together with a surprising off-centering of Mn2+ (d5) magnetic cations. This strong first-order phase transition is also evidenced by specific heat, dielectric, Raman, and infrared spectroscopy measurements. The magnetic characterizations indicate an anti-ferromagnetic (AFM) order below TN approximate to 20 K; analysis of powder neutron diffraction data confirms the magnetic structure with propagation vector k = (0 1 0) and collinear AFM spins. The observed jump in dielectric permittivity near similar to 150 K implies possible anti-ferroelectric behavior; however, the absence of switching suggests that Pb2MnTeO6 can only be antipolar. First-principle calculations confirmed that the crystal and magnetic structures determined are locally stable and that anti-ferroelectric switching is unlikely to be observed in Pb2MnTeO6.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.857
Times cited: 9
DOI: 10.1021/acs.inorgchem.6b00054
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“Tuning the crystal structure of A2CoPO4F(A=Li,Na) fluoride-phosphates : a new layered polymorph of LiNaCoPO4F”. Fedotov SS, Aksyonov DA, Samarin AS, Karakulina OM, Hadermann J, Stevenson KJ, Khasanova NR, Abakumov AM, Antipov E V, European journal of inorganic chemistry 2019, 4365 (2019). http://doi.org/10.1002/EJIC.201900660
Abstract: Co-containing fluoride-phosphates are of interest in sense of delivering high electrode potentials and attractive specific energy values as positive electrode materials for rechargeable batteries. In this paper we report on a new Co-based fluoride-phosphate, LiNaCoPO4F, with a layered structure (2D), which was Rietveld-refined based on X-ray powder diffraction data [P2(1)/c, a = 6.83881(4) angstrom, b = 11.23323(5) angstrom, c = 5.07654(2) angstrom, beta = 90.3517(5) degrees, V = 389.982(3) angstrom(3)] and validated by electron diffraction and high-resolution scanning transmission electron microscopy. The differential scanning calorimetry measurements revealed that 2D-LiNaCoPO4F forms in a narrow temperature range of 520-530 degrees C and irreversibly converts to the known 3D-LiNaCoPO4F modification (Pnma) above 530 degrees C. The non-carbon-coated 2D-LiNaCoPO4F shows reversible electrochemical activity in Li-ion cell in the potential range of 3.0-4.9 V vs. Li/Li+ with an average potential of approximate to 4.5 V and in Na-ion cell in the range of 3.0-4.5 V vs. Na/Na+ exhibiting a plateau profile centered around 4.2 V, in agreement with the calculated potentials by density functional theory. The energy barriers for both Li+ and Na+ migration in 2D-LiNaCoPO4F amount to 0.15 eV along the [001] direction rendering 2D-LiNaCoPO4F as a viable electrode material for high-power Li- and Na-ion rechargeable batteries. The discovery and stabilization of the 2D-LiNaCoPO4F polymorph indicates that temperature influence on the synthesis of A(2)MPO(4)F fluoride-phosphates needs more careful examination with perspective to unveil new structures.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.444
DOI: 10.1002/EJIC.201900660
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“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”. Morozov VA, Bertha A, Meert KW, Van Rompaey S, Batuk D, Martinez GT, Van Aert S, Smet PF, Raskina MV, Poelman D, Abakumov AM, Hadermann J;, Chemistry of materials 25, 4387 (2013). http://doi.org/10.1021/cm402729r
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.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 63
DOI: 10.1021/cm402729r
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“Superspace description, crystal structures, and electric conductiof the Ba4In6-xMgxO13-x/2 solid solutions”. Abakumov AM, Rossell MD, Gutnikova OY, Drozhzhin OA, Leonova LS, Dobrovolsky YA, Istomin SY, Van Tendeloo G, Antipov EV, Chemistry of materials 20, 4457 (2008). http://doi.org/10.1021/cm8004216
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 15
DOI: 10.1021/cm8004216
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“Article Structure and magnetic properties of BiFe0.75Mn0.25O3 perovskite prepared at ambient and high pressure”. Belik AA, Abakumov AM, Tsirlin AA, Hadermann J, Kim J, Van Tendeloo G, Takayama-Muromachi E, Chemistry of materials 23, 4505 (2011). http://doi.org/10.1021/cm201774y
Abstract: Solid solutions of BiFe1xMnxO3 (0.0 ≤ x ≤ 0.4) were prepared at ambient pressure and at 6 GPa. The ambient-pressure (AP) phases crystallize in space group R3c similarly to BiFeO3. The high-pressure (HP) phases crystallize in space group R3c for x = 0.05 and in space group Pnma for 0.15 ≤ x ≤ 0.4. The structure of HP-BiFe0.75Mn0.25O3 was investigated using synchrotron X-ray powder diffraction, electron diffraction, and transmission electron microscopy. HP-BiFe0.75Mn0.25O3 has a PbZrO3-related √2ap × 4ap × 2√2ap (ap is the parameter of the cubic perovskite subcell) superstructure with a = 5.60125(9) Å, b = 15.6610(2) Å, and c = 11.2515(2) Å similar to that of Bi0.82La0.18FeO3. A remarkable feature of this structure is the unconventional octahedral tilt system, with the primary ab0a tilt superimposed on pairwise clockwise and counterclockwise rotations around the b-axis according to the oioi sequence (o stands for out-of-phase tilt, and i stands for in-phase tilt). The (FeMn)O6 octahedra are distorted, with one longer metaloxygen bond (2.222.23 Å) that can be attributed to a compensation for covalent BiO bonding. Such bonding results in the localization of the lone electron pair on Bi3+ cations, as confirmed by electron localization function analysis. The relationship between HP-BiFe0.75Mn0.25O3 and antiferroelectric structures of PbZrO3 and NaNbO3 is discussed. On heating in air, HP-BiFe0.75Mn0.25O3 irreversibly transforms to AP-BiFe0.75Mn0.25O3 starting from about 600 K. Both AP and HP phases undergo an antiferromagnetic ordering at TN ≈ 485 and 520 K, respectively, and develop a weak net magnetic moment at low temperatures. Additionally, ceramic samples of AP-BiFe0.75Mn0.25O3 show a peculiar phenomenon of magnetization reversal.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 57
DOI: 10.1021/cm201774y
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“Transmission electron microscopic study of the defect structure in Sr4Fe6O12+\delta compounds with variable oxygen content”. Rossell MD, Abakumov AM, Van Tendeloo G, Lomakov MV, Istomin SY, Antipov EV, Chemistry and materials 17, 4717 (2005). http://doi.org/10.1021/cm050777x
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 17
DOI: 10.1021/cm050777x
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“Incommensurately modulated structures and luminescence properties of the AgxSm(2-x)/3WO4 (x=0.286, 0.2) scheelites as thermographic phosphors”. Morozov V, Deyneko D, Basoyich O, Khaikina EG, Spassky D, Morozov A, Chernyshev V, Abakumov A, Hadermann J, Chemistry of materials 30, 4788 (2018). http://doi.org/10.1021/ACS.CHEMMATER.8B02029
Abstract: Ag+ for Sm3+ substitution in the scheelite-type AgxSm(2-x)/3 square(1-2x)/3WO4 tungstates has been investigated for its influence on the cation-vacancy ordering and luminescence properties. A solid state method was used to synthesize the x = 0.286 and x = 0.2 compounds, which exhibited (3 + 1)D incommensurately modulated structures in the transmission electron microscopy study. Their structures were refined using high resolution synchrotron powder X-ray diffraction data. Under near-ultraviolet light, both compounds show the characteristic emission lines for (4)G(5/2) -> H-6(J) (J = 5/2, 7/2, 9/2, and 11/2) transitions of the Sm3+ ions in the range 550-720 nm, with the J = 9/2 transition at the similar to 648 nm region being dominant for all photoluminescence spectra. The intensities of the (4)G(5/2) -> H-6(9/2) and (4)G(5/2) -> H-6(7/2) bands have different temperature dependencies. The emission intensity ratios (R) for these bands vary reproducibly with temperature, allowing the use of these materials as thermographic phosphors.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 2
DOI: 10.1021/ACS.CHEMMATER.8B02029
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“Understanding the roles of anionic redox and oxygen release during electrochemical cycling of lithium-rich layered Li4FeSbO6”. McCalla E, Sougrati MT, Rousse G, Berg EJ, Abakumov A, Recham N, Ramesha K, Sathiya M, Dominko R, Van Tendeloo G, Novák P, Tarascon JM;, Journal of the American Chemical Society 137, 4804 (2015). http://doi.org/10.1021/jacs.5b01424
Abstract: Li-rich oxides continue to be of immense interest as potential next generation Li-ion battery positive electrodes, and yet the role of oxygen during cycling is still poorly understood. Here, the complex electrochemical behavior of Li4FeSbO6 materials is studied thoroughly with a variety of methods. Herein, we show that oxygen release occurs at a distinct voltage plateau from the peroxo/superoxo formation making this material ideal for revealing new aspects of oxygen redox processes in Li-rich oxides. Moreover, we directly demonstrate the limited reversibility of the oxygenated species (O-2(n-); n = 1, 2, 3) for the first time. We also find that during charge to 4.2 V iron is oxidized from +3 to an unusual +4 state with the concomitant formation of oxygenated species. Upon further charge to 5.0 V, an oxygen release process associated with the reduction of iron +4 to +3 is present, indicative of the reductive coupling mechanism between oxygen and metals previously reported. Thus, in full state of charge, lithium removal is fully compensated by oxygen only, as the iron and antimony are both very close to their pristine states. Besides, this charging step results in complex phase transformations that are ultimately destructive to the crystallinity of the material. Such findings again demonstrate the vital importance of fully understanding the behavior of oxygen in such systems. The consequences of these new aspects of the electrochemical behavior of lithium-rich oxides are discussed in detail.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 13.858
Times cited: 86
DOI: 10.1021/jacs.5b01424
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“Synthesis and crystal structure of novel CaRMnSnO6(R = La, Pr, Nd, Sm-Dy) double perovskites”. Abakumov AM, Rossell MD, Seryakov SA, Rozova MG, Markina MM, Van Tendeloo G, Antipov EV, Journal of materials chemistry 15, 4899 (2005). http://doi.org/10.1039/b510242a
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Times cited: 8
DOI: 10.1039/b510242a
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“Layered perovskite-like Pb2Fe2O5 structure as a parent matrix for the nucleation and growth of crystallographic shear planes”. Batuk D, Hadermann J, Abakumov A, Vranken T, Hardy A, van Bael M, Van Tendeloo G, Inorganic chemistry 50, 4978 (2011). http://doi.org/10.1021/ic200211x
Abstract: The Pb2Fe2O5 compound with a layered intergrowth structure has been prepared by a solid-state reaction at 700 °C. The incommensurate compound crystallizes in a tetragonal system with a = 3.9037(2) Å, c = 3.9996(4) Å, and q = 0.1186(4)c*, or when treated as a commensurate approximant, a = 3.9047(2) Å, c = 36.000(3) Å, space group I4/mmm. The crystal structure of Pb2Fe2O5 was resolved from transmission electron microscopy data. Atomic coordinates and occupancies of the cation positions were estimated from high-angle annular dark-field scanning transmission electron microscopy data. Direct visualization of the positions of the oxygen atoms was possible using annular bright-field scanning transmission electron microscopy. The structure can be represented as an intergrowth of perovskite blocks and partially disordered blocks with a structure similar to that of the Bi2O2 blocks in Aurivillius-type phases. The A-cation positions at the border of the perovskite block and the cation positions in the Aurivillius-type blocks are jointly occupied by Pb2+ and Fe3+ cations, resulting in a layer sequence along the c axis: PbOFeO2PbOFeO2Pb7/8Fe1/8O1xFe5/8Pb3/8O2Fe5/8Pb3/8. Upon heating, the layered Pb2Fe2O5 structure transforms into an anion-deficient perovskite modulated by periodically spaced crystallographic shear (CS) planes. Considering the layered Pb2Fe2O5 structure as a parent matrix for the nucleation and growth of CS planes allows an explanation of the specific microstructure observed for the CS structures in the PbFeO system.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.857
Times cited: 16
DOI: 10.1021/ic200211x
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“Polyoxocationic antimony oxide cluster with acidic protons”. Watanabe Y, Hyeon-Deuk K, Yamamoto T, Yabuuchi M, Karakulina OM, Noda Y, Kurihara T, Chang I-Y, Higashi M, Tomita O, Tassel C, Kato D, Xia J, Goto T, Brown CM, Shimoyama Y, Ogiwara N, Hadermann J, Abakumov AM, Uchida S, Abe R, Kageyama H, Science Advances 8, eabm5379 (2022). http://doi.org/10.1126/SCIADV.ABM5379
Abstract: The success and continued expansion of research on metal-oxo clusters owe largely to their structural richness and wide range of functions. However, while most of them known to date are negatively charged polyoxometalates, there is only a handful of cationic ones, much less functional ones. Here, we show an all-inorganic hydroxyiodide [H(10.)7Sb(32.1)O(44)][H2.1Sb2.1I8O6][Sb0.76I6](2)center dot 25H(2)O (HSbOI), forming a face-centered cubic structure with cationic Sb32O44 clusters and two types of anionic clusters in its interstitial spaces. Although it is submicrometer in size, electron diffraction tomography of HSbOI allowed the construction of the initial structural model, followed by powder Rietveld refinement to reach the final structure. The cationic cluster is characterized by the presence of acidic protons on its surface due to substantial Sb3+ deficiencies, which enables HSbOI to serve as an excellent solid acid catalyst. These results open up a frontier for the exploration and functionalization of cationic metal-oxo clusters containing heavy main group elements.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 13.6
DOI: 10.1126/SCIADV.ABM5379
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“KEu(MoO4)2 : polymorphism, structures, and luminescent properties”. Morozov VA, Arakcheeva AV, Pattison P, Meert KW, Smet PF, Poelman D, Gauquelin N, Verbeeck J, Abakumov AM, Hadermann J, Chemistry of materials 27, 5519 (2015). http://doi.org/10.1021/acs.chemmater.5b01622
Abstract: In this paper, with the example of two different polymorphs of KEu(MoO4)2, the influence of the ordering of the A-cations on the luminescent properties in scheelite related compounds (A′,A″)n[(B′,B″)O4]m is investigated. The polymorphs were synthesized using a solid state method. The study confirmed the existence of only two polymorphic forms at annealing temperature range 9231203 K and ambient pressure: a low temperature anorthic α-phase and a monoclinic high temperature β-phase with an incommensurately modulated structure. The structures of both polymorphs were solved using transmission electron microscopy and refined from synchrotron powder X-ray diffraction data. The monoclinic β-KEu(MoO4)2 has a (3+1)-dimensional incommensurately modulated structure (superspace group I2/b(αβ0)00, a = 5.52645(4) Å, b = 5.28277(4) Å, c = 11.73797(8) Å, γ = 91.2189(4)o, q = 0.56821(2)a*0.12388(3)b*), whereas the anorthic α-phase is (3+1)-dimensional commensurately modulated (superspace group I1̅(αβγ)0, a = 5.58727(22) Å, b = 5.29188(18)Å, c = 11.7120(4) Å, α = 90.485(3)o, β = 88.074(3)o, γ = 91.0270(23)o, q = 1/2a* + 1/2c*). In both cases the modulation arises due to Eu/K cation ordering at the A site: the formation of a 2-dimensional Eu3+ network is characteristic for the α-phase, while a 3-dimensional Eu3+-framework is observed for the β-phase structure. The luminescent properties of KEu(MoO4)2 samples prepared under different annealing conditions were measured, and the relation between their optical properties and their structures is discussed.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 26
DOI: 10.1021/acs.chemmater.5b01622
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“Coupled cation and charge ordering in the CaMn306 tunnel structure”. Hadermann J, Abakumov AM, Gillie LJ, Martin C, Hervieu M, Chemistry of materials 18, 5530 (2006). http://doi.org/10.1021/cm0618998
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 33
DOI: 10.1021/cm0618998
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“Chemistry, local molybdenum clustering, and electrochemistry in the Li2+xMo1-xO3 solid solutions”. Savina AA, Saiutina VV, Morozov AV, Boev AO, Aksyonov DA, Dejoie C, Batuk M, Bals S, Hadermann J, Abakumov AM, Inorganic chemistry 61, 5637 (2022). http://doi.org/10.1021/ACS.INORGCHEM.2C00420
Abstract: A broad range of cationic nonstoichiometry has been demonstratedfor the Li-rich layered rock-salt-type oxide Li2MoO3, which has generally been considered as a phase with a well-defined chemical composition. Li2+xMo1-xO3(-0.037 <= x <= 0.124) solid solutions were synthesized via hydrogen reduction ofLi2MoO4in the temperature range of 650-1100 degrees C, withxdecreasing with theincrease of the reduction temperature. The solid solutions adopt a monoclinicallydistorted O3-type layered average structure and demonstrate a robust localordering of the Li cations and Mo3triangular clusters within the mixed Li/Mocationic layers. The local structure was scrutinized in detail by electron diffractionand aberration-corrected scanning transmission electron microcopy (STEM),resulting in an ordering model comprising a uniform distribution of the Mo3clusters compatible with local electroneutrality and chemical composition. The geometry of the triangular clusters with their oxygenenvironment (Mo3O13groups) has been directly visualized using differential phase contrast STEM imaging. The established localstructure was used as input for density functional theory (DFT)-based calculations; they support the proposed atomic arrangementand provide a plausible explanation for the staircase galvanostatic charge profiles upon electrochemical Li+extraction fromLi2+xMo1-xO3in Li cells. According to DFT, all electrochemical capacity in Li2+xMo1-xO3solely originates from the cationic Moredox process, which proceeds via oxidation of the Mo3triangular clusters into bent Mo3chains where the electronic capacity of the clusters depends on the initial chemical composition and Mo oxidation state defining the width of the first charge low-voltageplateau. Further oxidation at the high-voltage plateau proceeds through decomposition of the Mo3chains into Mo2dimers and further into individual Mo6+cations
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.6
Times cited: 3
DOI: 10.1021/ACS.INORGCHEM.2C00420
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