Browsing by Author "Xia, Q"

Now showing 1 - 9 of 9
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    Crystal and magnetic structures of melilite-type Ba2MnSi2O7
    (American Chemical Society, 2019-03-06) Sale, M; Xia, Q; Avdeev, M; Ling, CD
    Melilite-type Ba2MnSi2O7 was synthesized by a standard powder solid-state reaction route, and its magnetic properties were studied at low temperature. The magnetic structure was found to be C-type pointing along the c axis from neutron powder diffraction, which is different from the G-type ordering previously reported in all other 2-2-4-2 melilites with manganese as the B′-site transition metal. Ab initio (density functional theory) and magnetic dipole–dipole calculations were used to understand the magnetic structure by determining the spin supersuperexchange parameters as well as the relative influence of spin–orbit coupling and the magnetic dipole–dipole interactions. © 2019 American Chemical Society
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    Crystal structure and monoclinic distortion of glaserite-type Ba3MnSi2O8
    (Elsevier, 2018-10-01) Avdeev, M; Xia, Q; Sale, M; Allison, MC; Ling, CD
    Crystal structure and magnetic properties of glaserite-type Ba3MnSi2O8 were investigated using variable temperature neutron powder diffraction and magnetometry. At room temperature the composition is hexagonal and the crystal structure is best described by the P-3m1 space group (a~ 5.7 Å, c~ 7.3 Å) with the apical oxygen atom modelled on a split site. On cooling below ~ 250 K the structure undergoes a phase transition into a monoclinic C2/c form (√3ahex, ahex, 2chex, β~ 90°). Analysing diffraction data in terms of symmetry-adapted distortion modes suggests that the transition is primarily driven by increasing in-plane displacements of O1, which in turn results in the coupled tilting of [SiO4] and [MnO6] octahedra and in-plane displacements of Ba1 atoms. Magnetic susceptibility measurements and neutron powder diffraction data show no evidence for long-range magnetic ordering down to 1.6 K, although the development of magnetic diffuse scattering suggests that a magnetic transition may take place at lower temperature. Crown Copyright © 2018 Published by Elsevier Inc.
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    Integration of ice-core, marine and terrestrial records for the Australian Last Glacial Maximum and Termination: a contribution from the OZ INTIMATE group
    (Wiley, 2006-10) Turney, CSM; Haberle, SG; Fink, D; Kershaw, AP; Barbetti, M; Barrows, TT; Black, M; Cohen, TJ; Corrège, T; Hesse, PP; Hua, Q; Johnston, R; Morgan, VI; Moss, PT; Nanson, GC; van Ommen, TD; Rule, S; Williams, NJ; Zhao, JX; D'Costa, D; Feng, YX; Gagan, MK; Mooney, SD; Xia, Q
    The degree to which Southern Hemisphere climatic changes during the end of the last glacial period and early Holocene (30-8 ka) were influenced or initiated by events occurring in the high latitudes of the Northern Hemisphere is a complex issue. There is conflicting evidence for the degree of hemispheric ‘teleconnection’ and an unresolved debate as to the principle forcing mechanism(s). The available hypotheses are difficult to test robustly, however, because the few detailed palaeoclimatic records in the Southern Hemisphere are widely dispersed and lack duplication. Here we present climatic and environmental reconstructions from across Australia, a key region of the Southern Hemisphere because of the range of environments it covers and the potentially important role regional atmospheric and oceanic controls play in global climate change. We identify a general scheme of events for the end of the last glacial period and early Holocene but a detailed reconstruction proved problematic. Significant progress in climate quantification and geochronological control is now urgently required to robustly investigate change through this period. © 2006 John Wiley & Sons, Ltd.
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    Manganese 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, CD
    We 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.
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    Multiple competing magnetic interactions in Na4Ni7(PO4)6
    (American Chemical Society, 2019-07-22) Xia, Q; Wang, CH; Schmid, S; Avdeev, M; Ling, CD
    The low-temperature magnetic behavior and ground state of the candidate sodium-ion battery cathode compound Na4Ni7(PO4)6 have been investigated by physical property measurements and neutron powder diffraction. On cooling, Na4Ni7(PO4)6 undergoes three successive long-range spin ordering transitions to Phase I (below TN = 17 K), Phase II (below TN′ = 9.1 K), and Phase III (below TN″ = 4.6 K) with ordering vectors [0, 1, 1/2], [0, 2/3, 1/2], and [∼0.076, 2/3, 1/2], respectively. All three magnetic phases can be described in terms of ferromagnetic Ni2+ stripes with antiferromagnetic interactions between them. The moment amplitude of all stripes is the same in Phase I but varies in Phase II, while Phase III is an incommensurate variation on Phase II. Phases I and II both feature a crystallographically unique Ni site with no ordered magnetic moment due to geometric frustration; the resolution of which may be the driving force behind the final transition to Phase III. Even among transition-metal phosphates, which typically show complex spin ordering due to competition between superexchange and super-superexchange (through PO4 linkers), Na4Ni7(PO4)6 has one of the richest magnetic phase diagrams explored so far. © 2019 American Chemical Society
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    New electrode materials for lithium- and sodium-ion batteries
    (Society of Crystallographers in Australia and New Zealand, 2017-12-03) Xia, Q; Ling, CD; Wang, C; Avdeev, M
    As a result of increased energy demand, energy storage has become a growing global concern over the past decade. Electrochemical energy storage (EES) technologies based on batteries are beginning to show considerable promise as a result of many breakthroughs in the last few years due to their appealing features including high round-trip efficiency, flexible power, energy characteristics to meet different grid functions, long cycle life, and low maintenance [1, 2]. My project focuses on the discovery, characterisation and optimisation of electrode and solid electrolyte materials in both lithium-ion batteries and sodium-ion batteries, in which the investigation of nuclear materials and magnetic structures and the dynamics of Li/Na ion are key issues. In this presentation three techniques below that have been heavily utilised to theoretically and experimentally characterise new electrode materials will be systematically discussed. 1. Ab initio calculation—It is employed to identify and compare the energies of framework structures with hosting Li/Na from materials data mining, which give an improved understanding of how the experimentally determined structures arise and how they will evolve with mobile ion concentration under electrochemical cycling. Knowledge of the ground-state magnetic structure also permits the accurate calculation of redox potentials, in conjunction with electrochemical measurements. 2. Neutron scattering—It concerns new crystalline materials for light metal-ion batteries in several ways. Neutron diffraction reveals the location and occupancies of Li/Na sites in the crystal lattice and, hence, conduction pathways. In situ experiments explicitly reveal Li/Na ion mobility, as well as phase changes under operating conditions that undermine long-term stability. Inelastic and quasielastic neutron scattering probe the dynamics of the mobile ions and the supporting lattice. Besides, low temperature neutron diffraction reveals the spin-ordered ground states of the transition metal countercations, which are not only fundamentally fascinating due to their complex super-super-exchange pathways, but also characteristic of their electrochemical states in batteries. 3. In-situ TEM characterisation—It is performed to study how materials degrade on a larger scale over repeated cycling: nanocrystallisation, and changes in the roughness of the interfaces. The information of the materials failure collected by virtue of this technique will help to effectively design accurate ways to optimise the materials.
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    Nickel 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, CD
    Lithium 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
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    Structure evolution of Na2O2 from room temperature to 500 °C
    (American Chemical Society, 2020-09-21) Wang, CH; Gui, DY; Xia, Q; Avdeev, M; Ling, CD; Kennedy, BJ
    Na2O2 is one of the possible discharge products from sodium–air batteries. Here, we report the evolution of the structure of Na2O2 from room temperature to 500 °C using variable-temperature neutron and synchrotron X-ray powder diffraction. A phase transition from α-Na2O2 to β-Na2O2 is observed in the neutron diffraction measurements above 400 °C, and the crystal structure of β-Na2O2 is determined from neutron diffraction data at 500 °C. α-Na2O2 adapts a hexagonal P62m (no. 189) structure, and β-Na2O2 adapts a tetragonal I41/acd (no. 142) structure. The thermal expansion coefficients of α-Na2O2 are a = 2.98(1) × 10–5 K–1, c = 2.89(1) × 10–5 K–1, and V = 8.96(1) × 10–5 K–1 up to 400 °C, and a ∼10% volume expansion occurs during the phase transition from α-Na2O2 to β-Na2O2 due to the realignment/rotation of O22– groups. Both phases are electronic insulators according to DFT calculations with band gaps (both indirect) of 1.75 eV (α-Na2O2) and 2.56 eV (β-Na2O2). An impedance analysis from room temperature to 400 °C revealed a significant enhancement of the conductivity at T ≥ 275 °C. α-Na2O2 shows a higher conductivity (∼10 times at T ≤ 275 °C and ∼3 times at T > 275 °C) in O2 compared to in Ar. We confirmed, by dielectric analysis, that this enhanced conductivity is dominated by ionic conduction. © 2020 American Chemical Society
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    Synthesis-controlled polymorphism and magnetic and electrochemical properties of Li3Co2SbO6
    (American Chemical Society, 2019-10-04) Brown, AJ; Xia, Q; Avdeev, M; Kennedy, BJ; Ling, CD
    Li3Co2SbO6 is found to adopt two highly distinct structural forms: a pseudohexagonal (monoclinic C2/m) layered O3-LiCoO2 type phase with “honeycomb” 2:1 ordering of Co and Sb, and an orthorhombic Fddd phase, isostructural with Li3Co2TaO6 but with the addition of significant Li/Co ordering. Pure samples of both phases can be obtained by conventional solid-state synthesis via a precursor route using Li3SbO4 and CoO, by controlling particle size, initial lithium excess, and reaction time. Both phases show relatively poor performance as lithium-ion battery cathode materials in their as-made states, but complex and interesting low-temperature magnetic properties. The honeycomb phase is the first of its type to show A-type antiferromagnetic order (ferromagnetic planes, antiferromagnetically coupled) below TN = 14 K. Isothermal magnetization and in-field neutron diffraction below TN show clear evidence for a metamagnetic transition at H ≈ 0.7 T to three-dimensional ferromagnetic order. The orthorhombic phase orders antiferromagnetically below TN = 112 K and then undergoes two more transitions at 80 and 60 K. Neutron diffraction data show that the ground state is incommensurate. © 2019 American Chemical Society