Browsing by Author "Johannessen, B"
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- ItemControlled one‐pot synthesis of nickel single atoms embedded in carbon nanotube and graphene supports with high loading(Wiley, 2020-04-09) Zhao, S; Wang, T; Zhou, G; Zhang, L; Lin, C; Veder, JP; Johannessen, B; Saunders, M; Yin, L; Liu, C; De Marco, R; Yang, SZ; Zhang, Q; Jiang, SPSingle‐atom catalysts (SACs) have attracted much attentions due to the advantages of high catalysis efficiency and selectivity. However, the controllable and efficient synthesis of SACs remains a significant challenge. Herein, we report a controlled one‐pot synthesis of nickel single atoms embedded on nitrogen‐doped carbon nanotubes (NiSA−N−CNT) and nitrogen‐doped graphene (NiSA−N−G). The formation of NiSA−N−CNT is due to the solid‐to‐solid rolling up mechanism during the high temperature pyrolysis at 800 °C from the stacked and layered Ni‐doped g‐C3N4, g‐C3N4−Ni structure to a tubular CNT structure. Addition of citric acid introduces an amorphous carbon source on the layered g‐C3N4−Ni and after annealing at the same temperature of 800 °C, instead of formation of NiSA−N−CNT, Ni single atoms embedded in planar graphene type supports, NiSA−N−G were obtained. The density functional theory (DFT) calculation indicates the introduction of amorphous carbon source substantially reduces the structure fluctuation or curvature of layered g‐C3N4‐Ni intermediate products, thus interrupting the solid‐to‐solid rolling process and leading to the formation of planar graphene type supports for Ni single atoms. The as‐synthesized NiSA−N−G with Ni atomic loading of ∼6 wt% catalysts shows a better activity and stability for the CO2 reduction reaction (CO2RR) than NiSA−N−CNT with Ni atomic loading of ∼15 wt% due to the open and exposed Ni single atom active sites in NiSA−N−G. This study demonstrates for the first time the feasibility in the control of the microstructure of carbon supports in the synthesis of SACs. © 1999-2024 John Wiley & Sons, Inc or related companies. All rights reserved.
- ItemCu5SbO6 – synchrotron, neutron diffraction studies and magnetic properties(Australian Institute of Physics, 2011-02-04) Söhnel, T; Rey, E; Ling, CD; Avdeev, M; Johannessen, B; Wallwork, KS; Kremer, RK; Whangbo, MHOne very interesting compound in the system Cu/Sb/O is the mixed-valent Cu5SbO6 = (Cu1+(Cu2+ 2/3Sb5+ 1/3)O2) which is crystallising in the high temperature modification as a modified Delafossite structure type. Compounds like Delafossite, CuFeO2, is one of the few groups of compounds showing the rare property of multiferroic behaviour. In Cu5SbO6 the magnetically active brucite-like CuO2 layer is diluted in an ordered fashion with nonmagnetic Sb5+. Cu5SbO6 also shows a phase transition, which exhibits a rather complicated behaviour. It depends on the temperature and the reaction conditions (reactants for preparation, pressure, open or closed system). High resolution Synchrotron and neutron powder diffraction measurements could clearly distinguish between the high temperature and the low temperature modification and reveal an ordering (HT-modification) / disordering (LT-modification) effect of the Sb5+ and Cu2+ ions in the brucite-like layers. The LT-modification can also be assigned to what had wrongly been described in the literature as Cu4.5SbO5. XANES Cu-K edge measurements and NPD measurements should clarify a potential oxidation of the Cu1+ to Cu2+ and a connected additional inclusion of oxygen in the structure. According to magnetic measurements and DFT calculations the magnetic structure in Cu5SbO6 can be described with a short range ferromagnetic-antiferromagnetic interaction model of the (Cu2+) pairs in the (Cu2+ 2/3Sb5+ 1/3)O2 layers with a super-exchange via the nonmagnetic Sb5+ atoms. The systematic replacement of the non-magnetic Sb5+ with magnetically active M5+ ions should change the magnetic properties dramatically and could lead to an long range ordering in the system. First results of Mn and Mo doping will also be presented.
- ItemEnhancing the reaction kinetics and structural stability of high-voltage LiCoO 2 via polyanionic species anchoring(Royal Society of Chemistry (RSC), 2024-05-16) Zheng, W; Liang, GM; Guo, H; Li, JX; Zou, JS; Yuwono, JA; Shu, H; Zhang, S; Peterson, VK; Johannessen, B; Thomsen, L; Hu, WB; Guo, ZPIncreasing the charging voltage to 4.6 V directly enhances battery capacity and energy density of LiCoO2 cathodes for lithium-ion batteries. However, issues of the activated harmful phase evolution and surface instability in high-voltage LiCoO2 lead to dramatic battery capacity decay. Herein, polyanionic PO43− species have been successfully anchored at the surface of LiCoO2 materials, achieving superior battery performance. The polyanionic species acting as micro funnels at the material surface, could expand LiCoO2 surface lattice spacing by 10%, contributing to enhanced Li diffusion kinetics and consequent excellent rate performance of 164 mA h g−1 at 20C (1C = 274 mA g−1). Crucially, polyanionic species with high electronegativity could stabilize surface oxygen at high voltage by reducing O 2p and Co 3d orbital hybridization, thus suppressing surface Co migration and harmful H1–3 phase formation and leading to superior cycling stability with 84% capacity retention at 1C after 300 cycles. Furthermore, pouch cells containing modified LiCoO2 and Li metal electrodes deliver an ultra-high energy density of 513 W h kg−1 under high loadings of 32 mg cm−2. This work provides insightful directions for modifying the material surface structure to obtain high-energy-density cathodes with high-rate performance and long service life. © Royal Society of Chemistry 2024.
- ItemExpanded chemistry and mixed ionic-electronic conductivity in vanadium-substituted variants of γ-Ba4Nb2O9(International Union of Crystallography, 2021-08-14) Brown, AJ; Schwaighofer, B; Avdeev, M; Johannessen, B; Evans, IR; Ling, CDTwo new compositional series with the previously unique γ-Ba4Nb2O9 type structure, γ-Ba4VxTa2-xO9 and γ-Ba4VxNb2-xO9 (x = 0-2/3), have been synthesised via solid-state methods. Undoped Ba4Ta2O9 forms a 6H-perovskite type phase, but with sufficient V doping the γ-type phase is thermodynamically preferred and possibly more stable than γ-Ba4Nb2O9, forming at a 200 °C lower synthesis temperature. This is explained by the fact that Nb5+ ions in γ-Ba4Nb2O9 simultaneously occupy 4-, 5- and 6-coordinate sites in the oxide sublattice, which is less stable than allowing smaller V5+ to occupy the former and larger Ta5+ to occupy the latter. We characterised the structures of the new phases using a combination of X-ray and neutron powder diffraction. All compositions hydrate rapidly and extensively (up to 1/3 H2O per formula unit) under ambient conditions, like the parent γ-Ba4Nb2O9 phase, and show moderate but improved mixed-ionic electronic conduction. At lower temperatures the ionic conduction is predominately protonic, while at higher temperatures it is dominated by oxide and electron-hole conduction.
- ItemExpanded chemistry and proton conductivity in vanadium-substituted variants of γ-Ba4Nb2O9(American Chemical Society, 2021-09-09) Brown, AJ; Schwaighofer, B; Avdeev, M; Johannessen, B; Evans, IR; Ling, CDWe have substantially expanded the chemical phase space of the hitherto unique γ-Ba4Nb2O9 type structure by designing and synthesizing stoichiometric ordered analogues γ-Ba4V1/3Ta5/3O9 and γ-Ba4V1/3Nb5/3O9 and exploring the solid-solution series γ-Ba4VxTa2–xO9 and γ-Ba4VxNb2–xO9. Undoped Ba4Ta2O9 forms a 6H-perovskite type phase, but with sufficient V doping the γ-type phase is thermodynamically preferred and possibly more stable than γ-Ba4Nb2O9, forming at a 200 °C lower synthesis temperature. This is explained by the fact that Nb5+ ions in γ-Ba4Nb2O9 simultaneously occupy 4-, 5-, and 6-coordinate sites in the oxide sublattice, which is less stable than allowing smaller V5+ to occupy the former two and larger Ta5+ to occupy the latter. The x = 1/3 phase γ-Ba4V1/3Ta5/3O9 shows greatly improved ionic conduction compared to the x = 0 phase 6H-Ba4Ta2O9. We characterized the structures of the new phases using a combination of X-ray and neutron powder diffraction. All compositions hydrate rapidly and extensively (up to 1/3 H2O per formula unit) in ambient conditions, like the parent γ-Ba4Nb2O9 phase. At lower temperatures, the ionic conduction is predominately protonic, while at higher temperatures it is likely other charge carriers make increasing contributions.© 2021 American Chemical Society
- ItemFcc-hcp phase transformation in Co nanoparticles induced by swift heavy-ion irradiation(American Physical Society, 2009-09) Sprouster, DJ; Giulian, R; Schnohr, CS; Araujo, LL; Kluth, P; Byrne, AP; Foran, GJ; Johannessen, B; Ridgway, MCWe demonstrate a face-centered cubic (fcc) to hexagonally close-packed (hcp) phase transformation in spherical Co nanoparticles achieved via swift heavy-ion irradiation. Co nanoparticles of mean diameter 13.2 nm and fcc phase were first formed in amorphous SiO2 by ion implantation and thermal annealing and then irradiated at room temperature with 9-185 MeV Au ions. The crystallographic phase was identified with x-ray absorption spectroscopy and electron diffraction and quantified, as functions of the irradiation energy and fluence, with the former. The transformation was complete at low fluence prior to any change in nanoparticle shape or size and was governed by electronic stopping. A direct-impact mechanism was identified with the transformation interaction cross-section correlated with that of a molten ion track in amorphous SiO2. We suggest the shear stress resulting from the rapid thermal expansion about an ion track in amorphous SiO2 was sufficient to initiate the fcc-to-hcp phase transformation in the Co nanoparticles. © 2009, American Physical Society
- ItemA general approach to 3D-printed single-atom catalysts(Springer Nature Limited, 2023-01-02) Xie, FX; Cui, XL; Zhi, X; Yao, D; Johannessen, B; Lin, T; Tang, JN; Woodfield, TBF; Gu, L; Qiao, SZA mass production route to single-atom catalysts (SACs) is crucial for their end use application. To date, the direct fabrication of SACs via a simple and economic manufacturing route remains a challenge, with current approaches relying on convoluted processes using expensive components. Here, a straightforward and cost-effective three-dimensional (3D) printing approach is developed to fabricate a library of SACs. Despite changing synthetic parameters, including centre transition metal atom, metal loading, coordination environment and spatial geometry, the products show similar atomic dispersion nature of single metal sites, demonstrating the generality of the approach. The 3D-printed SACs exhibited excellent activity and stability in the nitrate reduction reaction. It is expected that this 3D-printing technique can be used as a method for large-scale commercial production of SACs, thus enabling the use of these materials in a broad spectrum of industrial applications. © 2023 The Author(s), under exclusive licence to Springer Nature Limited.
- ItemHigh-accuracy transmission and fluorescence XAFS of zinc at 10 K, 50 K, 100 K and 150 K using the hybrid technique(International Union of Crystallography, 2022-10-24) John, MW; Sier, D; Ekanayake, RSK; Schalken, MJ; Tran, CQ; Johannessen, B; de Jonge, MD; Kappen, P; Chantler, CTThe most accurate measurements of the mass attenuation coefficient for metals at low temperature for the zinc K-edge from 9.5 keV to 11.5 keV at temperatures of 10 K, 50 K, 100 K and 150 K using the hybrid technique are reported. This is the first time transition metal X-ray absorption fine structure (XAFS) has been studied using the hybrid technique and at low temperatures. This is also the first hybrid-like experiment at the Australian Synchrotron. The measured transmission and fluorescence XAFS spectra are compared and benchmarked against each other with detailed systematic analyses. A recent method for modelling self-absorption in fluorescence has been adapted and applied to a solid sample. The XAFS spectra are analysed using eFEFFIT to provide a robust measurement of the evolution of nanostructure, including such properties as net thermal expansion and mean-square relative displacement. This work investigates crystal dynamics, nanostructural evolution and the results of using the Debye and Einstein models to determine atomic positions. Accuracies achieved, when compared with the literature, exceed those achieved by both relative and differential XAFS, and represent a state-of-the-art for future structural investigations. Bond length uncertainties are of the order of 20–40 fm. © Open Access - CC BY 4.0 licence
- ItemInfluence of annealing conditions on the growth and structure of embedded Pt nanocrystals(American Institute of Physics, 2009-02-15) Giulian, R; Araujo, LL; Kluth, P; Sprouster, DJ; Schnohr, CS; Johannessen, B; Foran, GJ; Ridgway, MCThe growth and structure of Pt nanocrystals (NCs) formed by ion implantation in a-SiO2 has been investigated as a function of the annealing conditions. Transmission electron microscopy and small-angle x-ray scattering measurements demonstrate that the annealing ambient has a significant influence on NC size. Samples annealed in either Ar, O-2, or forming gas (95% N-2: 5% H-2) at temperatures ranging from 500 degrees C-1300 degrees C form spherical NCs with mean diameters ranging from 1-14 nm. For a given temperature, annealing in Ar yields the smallest NCs. O-2 and forming gas ambients produce NCs of comparable size though the latter induces H chemisorption at 1100 degrees C and above, as verified with x-ray absorption spectroscopy. This H intake is accompanied by a bond-length expansion and increased structural disorder in NCs of diameter >3 nm. © 2009, American Institute of Physics
- ItemInfluence of carbon support on the pyrolysis of cobalt phthalocyanine for the efficient electroreduction of CO2(American Chemical Society, 2022-11-14) Hamonnet, J; Bennington, MS; Johannessen, B; Hamilton, JL; Brooksby, PA; Brooker, S; Golovko, VB; Marshall, ATUnderstanding the nature of the reactive sites of CO2reduction catalysts is crucial to developing efficient and selective materials to help mitigate the greenhouse effect. In this research, materials based on cobalt phthalocyanine supported by carbon black and pyrolyzed at various temperatures under argon are fabricated and tested for CO2electroreduction. The results show that the high reactivity of the catalysts for the electroreduction of CO2to CO is maintained for materials prepared at temperatures up to 700 °C, with CO Faradaic efficiencies of >85% and CO current densities consistently at >40 mA cm-2at -0.86 V vs RHE. The materials annealed up to 900 °C are also remarkably active, with CO Faradaic efficiencies of >40% and CO current densities of >12 mA cm-2. The combination of X-ray diffraction, infrared and Raman spectroscopies, and X-ray absorption analysis show that the annealed materials exhibit chemical structures drastically different from those of the original CoPC and unsupported pyrolyzed catalyst while highlighting the role of the carbon black support in the formation of active species. These results give crucial insight into the reactive structure of CoPC and open the way for the development of pyrolyzed Co-N4macrocycles as a new class of materials efficient for the electroreduction of CO2,. © 2022 American Chemical Society.
- ItemIntroducing 4s–2p orbital hybridization to stabilize spinel oxide cathodes for lithium-ion batteries(Wiley-VCH GmbH, 2022-04-25) Liang, GM; Olsson, E; Zou, JS; Wu, ZB; Li, JX; Lu, CZ; D'Angelo, AM; Johannessen, B; Thomsen, L; Cowie, BCC; Peterson, VK; Cai, Q; Pang, WK; Guo, ZPOxides composed of an oxygen framework and interstitial cations are promising cathode materials for lithium-ion batteries. However, the instability of the oxygen framework under harsh operating conditions results in fast battery capacity decay, due to the weak orbital interactions between cations and oxygen (mainly 3d–2p interaction). Here, a robust and endurable oxygen framework is created by introducing strong 4s–2p orbital hybridization into the structure using LiNi0.5Mn1.5O4 oxide as an example. The modified oxide delivers extraordinarily stable battery performance, achieving 71.4 % capacity retention after 2000 cycles at 1 C. This work shows that an orbital-level understanding can be leveraged to engineer high structural stability of the anion oxygen framework of oxides. Moreover, the similarity of the oxygen lattice between oxide electrodes makes this approach extendable to other electrodes, with orbital-focused engineering a new avenue for the fundamental modification of battery materials. © 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH - Open access.
- ItemIon irradiation effects on metallic nanocrystals(Taylor & Francis, 2007-07) Kluth, P; Johannessen, B; Giulian, R; Schnohr, CS; Foran, GJ; Cookson, DJ; Byrne, AP; Ridgway, MCWe have investigated structural and morphological properties of metallic nanocrystals ( NCs) exposed to ion irradiation. NCs were characterized by transmission electron microscopy in combination with advanced synchrotron-based analytical techniques, in particular X-ray absorption spectroscopy and small-angle X-ray scattering. A number of different effects were observed depending on the irradiation conditions. At energies where nuclear stopping is predominant, structural disorder/amorphization followed by inverse Ostwald ripening/dissolution due to ion beam mixing was observed for Au and Cu NCs embedded in SiO2. The ion-irradiation-induced crystalline to amorphous transition in the NCs, which cannot be achieved in the corresponding bulk metals, was attributed to their initially higher structural energy as compared to bulk material and possibly preferential nucleation of the amorphous phase at the NC/SiO2 interface. At very high irradiation energies (swift heavy ion irradiation), where the energy loss is nearly entirely due to electronic stopping, a size-dependent shape transformation of the NCs from spheres to rod like shapes was apparent in Au NCs. Our preliminary results are in good agreement with considerations on melting of the NCs in the ion track as one mechanism involved in the shape transformation. © 2007, Taylor & Francis Ltd.
- ItemIon-irradiation-induced amorphization of Cu nanoparticles embedded in SiO2(American Physical Society, 2007-11) Johannessen, B; Kluth, P; Llewellyn, DJ; Foran, GJ; Cookson, DJ; Ridgway, MCElemental Cu nanoparticles embedded in SiO2 were irradiated with 5 MeV Sn3+. The nanoparticle structure was studied as a function of Sn3+ fluence by extended x-ray absorption fine structure spectroscopy, small-angle x-ray scattering, and transmission electron microscopy. Prior to irradiation, Cu nanoparticles exhibited the face-centered-cubic structure. Upon irradiation at intermediate fluences (1×1013 to 1×1014 ions/cm2), the first nearest neighbor Cu-Cu coordination number decreased, while the Debye-Waller factor, bondlength, and third cumulant of the bondlength distribution increased. In particular, at a fluence of 1×1014 ions/cm2 we argue for the presence of an amorphous Cu phase, for which we deduce the structural parameters. Low temperature annealing (insufficient for nanoparticle growth) of the amorphous Cu returned the nanoparticles to the initial preirradiation structure. At significantly higher irradiation fluences (1×1015 to 1×1016 ions/cm2), the nanoparticles were dissolved in the matrix with a Cu coordination similar to that of Cu2O. © 2007, American Physical Society
- ItemIon-irradiation-induced porosity in GaSb and InSb(Australian Institute of Physics, 2005-01-31) Kluth, SM; Johannessen, B; Kluth, P; Glover, CJ; Foran, GJ; Ridgway, MCIon irradiation of crystalline GaSb and InSb can yield not only amorphisation, as commonly observed in semiconductors, but also porosity. Extended x-ray absorption fine structure spectroscopy, electron microscopy and Rutherford backscattering spectrometry have been used to determine the exact nature of and relationship between these two transformations. In both materials, low dose, room temperature implantation produces spherical voids yet the material remains crystalline. With increasing implant dose, the porous layer eventually evolves into a network of straight rods 15nm in diameter. We suggest the porosity arises from preferential clustering of interstitials into extended defects and vacancies agglomerating to form voids.
- ItemIon-transport phenomena and anomalous transformations in strontium uranium oxides.(International Union of Crystallography, 2017-12-01) Murphy, GL; Zhang, Z; Avdeev, M; Wang, CH; Beridze, G; Kowalski, PM; Gu, QF; Kimpton, JA; Johannessen, B; Kennedy, BJStructural-chemical elucidation of low dimensional ternary uranium oxide systems is considered an essential aspect of thenuclear fuel cycle since understanding of their physicochemical properties may guide the storage and disposal of spentnuclear fuel [1]. The study of these systems allows for further exploration of the peculiar, exotic and poorly knownproperties of materials containing, or which can access, 5f electrons. SrUO₄ exemplifies this, a potential waste form resultingfrom reaction between spent UO₂+x fuel and the fission daughter Sr-90. We have found, through a combination of in situsynchrotron X-ray powder diffraction and X-ray absorption spectroscopy, that during its first order rhombohedral-orthorhombic transition under oxidising conditions, the rhombohedral form of SrUO₄, α, undergoes a spontaneousreduction of the uranium valence state through oxygen vacancy formation [2]. The process is synergetic, as the triality ofoxygen vacancy formation, subsequent ion diffusion and uranium reduction, seemingly reduces the activation energy barrierfor the transformation to the thermodynamically favoured stoichiometric orthorhombic form, β-SrUO₄. However formation ofthe orthorhombic form is only possible if a source of oxygen is present, without this, the oxygen deficient α-SrUO₄-xremains rhombohedral as shown by in situ neutron powder diffraction measurements. These experimental observations arefurther supported by ab initio DFT+U calculations using the self consistently calculated Hubbard U parameter values andbond valence sums calculations [2-3]. These methods indicate the affinity for α-SrUO₄-x to retain oxygen vacancies asopposed to β-SrUO₄, a consequence of the crystal lattice’s ability to stabilise the coordination environment of the Sr²⁺ cationvia the flexibility of uranium to undergo reduction through vacancy formation. CaUO4, isostructural to α-SrUO₄ , but unlike α-SrUO₄ does not have a stable orthorhombic polymorph as shown by both insitu synchrotron X-ray powder diffraction measurements and ab initio calculations. Introducing Sr ions into the CaUO₄ latticein the form of a solid solution, α-Sr₁-xCaxUO₄ (0 < x < 0.4), provides a means to atomically engineer the lattice to promoteoxygen vacancy formation, and presumably diffusion, at high temperatures. When CaUO₄ or α-SrUO₄ is treated underhighly reducing conditions, both materials undergo unusual reconstructive phase transformations at high temperatures to amonoclinic structure. These phase transformations are reversible, and cooling the sample yields the correspondingrhombohedral structure again. It is remarkable that the ordered monoclinic structure is favoured at high temperatures andthe disordered rhombohedral structure at low temperatures. This investigation in SrUO₄ highlights the rich and remarkablestructural chemistry and crystallography that may be found within poorly understood actinide systems whilst demonstratingthe successful marriage of experimental and theoretical approaches towards elucidating their chemical and physicalphenomena. © International Union of Crystallography
- ItemA long cycle-life high-voltage spinel lithium-ion battery electrode achieved by site-selective doping(John Wiley & Sons, Inc, 2020-03-23) Liang, GM; Wu, ZB; Didier, C; Zhang, WC; Cuan, J; Li, BH; Ko, KY; Hung, PY; Lu, CZ; Chen, YZ; Leniec, G; Kaczmarek, SM; Johannessen, B; Thomsen, L; Peterson, VK; Pang, WK; Guo, ZPSpinel LiNi0.5Mn1.5O4 (LNMO) is a promising cathode candidate for the next-generation high energy-density lithium-ion batteries (LIBs). Unfortunately, the application of LNMO is hindered by its poor cycle stability. Now, site-selectively doped LNMO electrode is prepared with exceptional durability. In this work, Mg is selectively doped onto both tetrahedral (8a) and octahedral (16c) sites in the Fdurn:x-wiley:14337851:media:anie202001454:anie202001454-math-0001 m structure. This site-selective doping not only suppresses unfavorable two-phase reactions and stabilizes the LNMO structure against structural deformation, but also mitigates the dissolution of Mn during cycling. Mg-doped LNMOs exhibit extraordinarily stable electrochemical performance in both half-cells and prototype full-batteries with novel TiNb2O7 counter-electrodes. This work pioneers an atomic-doping engineering strategy for electrode materials that could be extended to other energy materials to create high-performance devices. © 2020 Wiley-VCH Verlag GmbH & Co
- ItemManganese metaphosphate Mn(PO3)2 as a high‐performance negative electrode material for lithium‐ion batteries(Wiley, 2020-06-15) Xia, Q; Naeyaert, PJP; Avdeev, M; Schmid, S; Liu, H; Johannessen, B; Ling, CDWe report a novel negative conversion electrode material, manganese (II) metaphosphate Mn(PO3)2. This compound can be synthesized by a facile solid-state method, and after carbon-coating delivers an attractively high reversible capacity of 477 mAh/g at 0.1 C and 385 mAh/g at 1 C. We investigated the reaction mechanism with a combination of ex situ X-ray absorption spectroscopy, in situ X-ray diffraction, and high-resolution transmission electron microscopy. We observed a direct conversion process by monitoring the first discharge in operando, in which Mn(PO3)2 reacts with Li to give fusiform Mn nanograins a few Ångstroms in width, embedded in a matrix of lithium conducting LiPO3 glass. Due to the fine nanostructures of the conversion products, this conversion reaction is completely reversible. © 1999-2021 John Wiley & Sons, Inc.
- Item(Mg,Mn,Fe,Co,Ni)O: a rocksalt high-entropy oxide containing divalent Mn and Fe(American Association for the Advancement of Science, 2023-09-20) Pu, Y; Moseley, D; He, Z; Pitike, KC; Manley, ME; Yan, J; Cooper, VR; Mitchell, VD; Peterson, VK; Johannessen, B; Hermann, RP; Cao, PHigh-entropy oxides (HEOs) have aroused growing interest due to fundamental questions relating to their structure formation, phase stability, and the interplay between configurational disorder and physical and chemical properties. Introducing Fe(II) and Mn(II) into a rocksalt HEO is considered challenging, as theoretical analysis suggests that they are unstable in this structure under ambient conditions. Here, we develop a bottom-up method for synthesizing Mn- and Fe-containing rocksalt HEO (FeO-HEO). We present a comprehensive investigation of its crystal structure and the random cation-site occupancy. We show the improved structural robustness of this FeO-HEO and verify the viability of an oxygen sublattice as a buffer layer. Compositional analysis reveals the valence and spin state of the iron species. We further report the antiferromagnetic order of this FeO-HEO below the transition temperature ~218 K and predict the conditions of phase stability of Mn- and Fe-containing HEOs. Our results provide fresh insights into the design and property tailoring of emerging classes of HEOs. © 2024 American Association for the Advancement of Science.
- ItemNickel metaphosphate as a conversion positive electrode for lithium‐ion batteries(Wiley, 2020-06-09) Xia, Q; Avdeev, M; Schmid, S; Liu, H; Johannessen, B; Ling, CDLithium storage schemes based on conversion chemistry have been used in a large variety of negative electrodes achieving capacities 2–3 times higher than graphite. However, to date, relatively few positive electrode examples have been reported. Here, we report a new conversion positive electrode, Ni(PO3)2, and systematic studies on its working and degradation mechanisms. Crystalline Ni(PO3)2 undergoes an electrochemistry-driven amorphization process in the first discharge to form a fine microstructure, consisting of Ni domains ∼2 nm wide that form a percolating electron-conducting network, embedded in a glassy LiPO3 matrix. P does not participate electrochemically, remaining as P5+ in [PO3]− throughout. The electrode does not recrystallise in the following first charge process, remaining amorphous over all subsequent cycles. The low ionicity of the Ni−[PO3] bond and the high Li+ conductivity of the LiPO3 glass lead to high intrinsic electrochemical activity, allowing the micro-sized Ni(PO3)2 to achieve its theoretical capacity of 247 mAh/g. The performance of the Ni(PO3)2 electrode ultimately degrades due to the growth of larger and more isolated Ni grains. While the theoretical capacity of Ni(PO3)2 is itself limited, this study sheds new light on the underlying chemical mechanisms of conversion positive electrodes, an important new class of electrode for solid-state batteries. © 2020 Wiley-VCH GmbH
- ItemNonstoichiometry in strontium uranium oxide: understanding the rhombohedral–orthorhombic transition in SrUO4(American Chemical Society, 2016-08-29) Murphy, GL; Kennedy, BJ; Kimpton, JA; Gu, QF; Johannessen, B; Beridze, G; Kowalski, PM; Bosbach, D; Avdeev, M; Zhang, ZIn situ neutron and synchrotron X-ray diffraction studies demonstrate that SrUO4 acts as an oxygen transfer agent, forming oxygen vacancies under both oxidizing and reducing conditions. Two polymorphs of SrUO4 are stable at room temperature, and the transformation between these is observed to be associated with thermally regulated diffusion of oxygen ions, with partial reduction of the U6+ playing a role in both the formation of oxygen deficient α-SrUO4−δ and its subsequent transformation to stoichiometric β-SrUO4. This is supported by ab initio calculations using density functional theory calculations. The oxygen vacancies play a critical role in the first order transition that SrUO4 undergoes near 830 °C. The changes in the oxidation states and U geometry associated with the structural phase transition have been characterized using X-ray absorption spectroscopy, synchrotron X-ray diffraction, and neutron diffraction. © 2016 American Chemical Society