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    Temperature dependence of structure and ionic conductivity of LiTa2PO8 ceramics
    (American Chemical Society, 2022-11-30) Dai, R; Avdeev, M; Kim, SJ; Rao, RP; Adams, St
    LiTa2PO8 has recently been reported as a new fast Li-ion conducting structure type within the series of Lix(MO6/2)m(TO4/2)n polyanion oxides. Here, we demonstrate the preparation of LiTa2PO8 by solid-state syntheses, clarify the temperature dependence of lithium distribution and ionic conductivity, and study the structural stability, densification, and achievable total conductivity as a function of sintering conditions synergizing experimental neutron and X-ray powder diffraction and electrochemical studies with computational energy landscape analyses and molecular dynamics simulations. A total room temperature conductivity of 0.7 mS cm-1 with an activation energy of 0.27 eV is achieved after sintering at 1323 K for 10 h. Spark plasma sintering yields high densification >98%, highly reproducible bulk conductivities of 2.8 mS cm-1, in agreement with our bond valence site energy-based pathway predictions, and total conductivities of 0.6 mS cm-1 within minutes. Powder diffraction studies from 3 to 1273 K reveal a reversible flipping of the monoclinic angle from above to below 90° close to room temperature as a consequence of rearrangements of the mobile ions that change the detailed pathway topology. A consistent model of the temperature-dependent Li redistribution, conductivity anisotropy, and transport mechanism is derived from a synopsis of diffraction experiments, experimental conductivity studies, and simulations. Due to the limited electrochemical window of Lix(TaO6/2)2(PO4/2)1 (LTPO), a direct contact with Li metal or high voltage cathode materials leads to degradation, but as demonstrated in this work, semi-solid-state batteries, where LTPO is protected from direct contact with lithium by organic buffer layers, achieve stable cycling. © 2022 American Chemical Society
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    A customized strategy to design intercalation-type Li-free cathodes for all-solid-state batteries
    (Oxford University Press, 2023-01-10) Wang, D; Yu, J; Yin, X; Shao, S; Li, Q; Wang, YC; Avdeev, M; Chen, LQ; Shi, SQ
    Pairing Li-free transition-metal-based cathodes (MX) with Li-metal anodes is an emerging trend to overcome the energy-density limitation of current rechargeable Li-ion technology. However, the development of practical Li-free MX cathodes is plagued by the existing notion of low voltage due to the long-term overlooked voltage-tuning/phase-stability competition. Here, we propose a p-type alloying strategy involving three voltage/phase-evolution stages, of which each of the varying trends are quantitated by two improved ligand-field descriptors to balance the above contradiction. Following this, an intercalation-type 2H-V1.75Cr0.25S4 cathode tuned from layered MX2 family is successfully designed, which possesses an energy density of 554.3 Wh kg−1 at the electrode level accompanied by interfacial compatibility with sulfide solid-state electrolyte. The proposal of this class of materials is expected to break free from scarce or high-cost transition-metal (e.g. Co and Ni) reliance in current commercial cathodes. Our experiments further confirm the voltage and energy-density gains of 2H-V1.75Cr0.25S4. This strategy is not limited to specific Li-free cathodes and offers a solution to achieve high voltage and phase stability simultaneously. TheAuthor(s) 2023. Published byOxfordUniversity Press on behalf of China Science Publishing&Media Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License
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    NASICON-type air-stable and all-climate cathode for sodium-ion batteries with low cost and high-power density
    (Springer Nature, 2019-04-01) Chen, MZA; Hua, WB; Xiao, Jin; Cortie, DL; Chen, W; Wang, E; Hu, Z; Gu, QF; Wang, XL; Indris, S; Chou, SL; Dou, SX
    The development of low-cost and long-lasting all-climate cathode materials for the sodium ion battery has been one of the key issues for the success of large-scale energy storage. One option is the utilization of earth-abundant elements such as iron. Here, we synthesize a NASICON-type tuneable Na4Fe3(PO4)2(P2O7)/C nanocomposite which shows both excellent rate performance and outstanding cycling stability over more than 4400 cycles. Its air stability and all-climate properties are investigated, and its potential as the sodium host in full cells has been studied. A remarkably low volume change of 4.0% is observed. Its high sodium diffusion coefficient has been measured and analysed via first-principles calculations, and its three-dimensional sodium ion diffusion pathways are identified. Our results indicate that this low-cost and environmentally friendly Na4Fe3(PO4)2(P2O7)/C nanocomposite could be a competitive candidate material for sodium ion batteries. - © Open Access This article is licensed under a Creative Commons Attribution 4.0
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    Seasonal wetlands make a relatively limited contribution to the dissolved carbon pool of a lowland headwater tropical stream
    (American Geophysical Union (AGU), 2024-02-07) Solano, V; Duvert, C; Hutley, LB; Cendón, DI; Maher, DT; Birkel, C
    Wetlands process large amounts of carbon (C) that can be exported laterally to streams and rivers. However, our understanding of wetland inputs to streams remains unclear, particularly in tropical systems. Here we estimated the contribution of seasonal wetlands to the C pool of a lowland headwater stream in the Australian tropics. We measured dissolved organic and inorganic C (DOC and DIC) and dissolved gases (carbon dioxide—CO2, methane—CH4) during the wet season along the mainstem and in wetland drains connected to the stream. We also recorded hourly measurements of dissolved CO2 along a ‘stream–wetland drain–stream’ continuum, and used a hydrological model combined with a simple mass balance approach to assess the water, DIC and DOC sources to the stream. Seasonal wetlands contributed ∼15% and ∼16% of the DOC and DIC loads during our synoptic sampling, slightly higher than the percent area (∼9%) they occupy in the catchment. The riparian forest (75% of the DOC load) and groundwater inflows (58% of the DIC load) were identified as the main sources of stream DOC and DIC. Seasonal wetlands also contributed marginally to stream CO2 and CH4. Importantly, the rates of stream CO2 emission (1.86 g C s−1) and DOC mineralization (0.33 g C s−1) were much lower than the downstream export of DIC (6.39 g C s−1) and DOC (2.66 g g C s−1). This work highlights the need for further research on the role of riparian corridors as producers and conduits of terrestrial C to tropical streams. © 2024. The Authors. This is an open access article under the terms of the Creative Commons Attribution License.
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    Spin-wave propagation in α-Fe2O3 nanorods: the effect of confinement and disorder
    (IOP Publishing, 2019-03-07) Cortie, DL; Casillas-Garcia, G; Squires, A; Mole, RA; Wang, XL; Liu, Y; Chen, YH; Yu, DH
    Spin-wave excitations in α-Fe 2 O 3 nanorods were directly detected using time-of-flight inelastic neutron spectroscopy. The dispersive magnon features are compared with those in bulk α-Fe 2 O 3 particles at various temperatures to highlight differences in mode intensity and width. The interchanged spectral intensities in the nanorod are a consequence of a suppressed spin orientation, and this is also evident in the neutron diffraction which demonstates that the weak ferromagnetic phase survives to 1.5 K. Transmission electron microscopy shows that the ellipsoidal particles are single-crystalline with a typical length of 300 ± 100 nm and diameter of 60 ± 10 nm. The main magnon features are similar in bulk and nanoforms and can be explained using a model Hamiltonian based on Samuelson and Shirane's classical theory with exchange constants of J 1 = -1.03 meV, J 2 = -0.28 meV, J 3 = 5.12 meV and J 4 = 4.00 meV. Numerical simulations show that two distinct mechanisms may contribute to the magnon line broadening in the nanorods: a distribution of exchange interactions caused by disorder, and a shortened quasiparticle lifetime caused by the scattering of spin waves at surfaces. © 2019 IOP Publishing Ltd