Browsing by Author "Stansby, JH"

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    Biphasic P2/O3-Na2/3Li0.18Mn0.8Fe0.2O2: a structural investigation
    (Royal Society of Chemistry, 2020-12-22) Stansby, JH; Avdeev, M; Brand, HEA; Gonzalo, E; Drewett, NE; Ortiz-Vitoriano, N; Sharma, N; Rojo, T
    The P2/O3 layered oxide system is thought to benefit from a synergistic enhancement, resulting from the presence of both phases, which makes it a promising cathode material for Na-ion battery applications. Here, biphasic P2/O3-Na2/3Li0.18Mn0.8Fe0.2O2 is investigated via a combination of neutron and X-ray scattering techniques. Neutron diffraction data indicates that the O3 alkali metal site is fully occupied by Li. Real time operando X-ray diffraction data shows the structural evolution of the composite electrode – at the charged state there is no evidence of O2, OP4 or Z phases. The results presented herein provide new insight into site preference of Li in biphasic materials and highlights the value of utilizing multiple phases to achieve high performance layered cathode materials for sodium battery applications.© The Royal Society of Chemistry 2021
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    A combined DFT and NPD approach to determine the structure and composition of the ε-phase of tungsten boride
    (Elsevier, 2023-10-15) Setayandeh, SS; Stansby, JH; Obbard, EG; Brand, MI; Miskovic, DM; Laws, KJ; Peterson, VK; Astbury, JO; Wilson, CL; Irukuvarghula, S; Burr, PA
    The ε-phase of tungsten boride, conventionally labelled as W2B5, has been identified as a promising candidate for shielding application in spherical tokamak fusion reactors. However, further research has been hindered by a lack of agreement on the structure and even composition of the ε-phase. Here, we identify the stable crystal structure and stoichiometry range of ε tungsten borides through a combination of ab initio simulations and neutron diffraction of isotopically enriched samples. We considered the ability to accommodate hypo-stoichiometry in six published structures of the ε phase. Chemical disorder was modelled using configurational ensembles to account for entropy of non-stoichiometry. We show that two W2B4-x structures (with x=∼0.25 − 0.5), with space group symmetry P63/mmc and P63/mcm, appear to be thermodynamically stable. These candidate compounds have 6.2 − 7.8 at.% less B than the W2B5 composition reported in exiting phase diagrams. We confirm these findings by means of neutron powder diffraction, performed on 11B-enriched arc-melted and crushed samples. Rietveld refinement using the neutron data shows the ε-phase to be better described as W2B3.60(2) (P63/mcm), in keeping with density functional theory (DFT) calculations. Linear change in DFT-derived lattice parameters of the candidates for the ε-phase proposes a simple model to assess the tungsten boride composition by measuring the lattice parameter (e.g. by X-ray diffraction. The simulations also reveal that the material can accommodate a range of stoichiometric variations (via B vacancies) with relatively small stored energy, which is a desirable feature for neutron shielding application. © 2023 The Authors. Published by Elsevier Ltd on behalf of Acta Materialia Inc. Open Access CC-NC-ND
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    Crystallographic characterization of U2CrN3: a neutron diffraction and transmission electron microscopy approach
    (Elsevier, 2023-06) Patnaik, S; Mishchenko, Y; Stansby, JH; Fazi, A; Peterson, VK; Jädernäs, D; Thuvander, M; Johnson, KD; Obbard, EG; Lopes, DA
    In this study, neutron diffraction and transmission electron microscopy (TEM) have been implemented to study the crystallographic structure of the ternary phase U2CrN3 from pellet to nano scale respectively. Recently microstructural evaluation of this ternary phase has been performed for the first time in pellet condition, overcoming the Cr evaporation issue during the conventional sintering process. In this work for the first time, the crystallographic structure of the ordered ternary U2CrN3 phase, stabilized in pellet condition, has been obtained by implementing neutron diffraction. For this study, pellets of the composite material UN with 20 vol% CrN were fabricated by powder metallurgy by mixing UN and CrN powders followed by Spark Plasma Sintering (SPS). TEM was used to investigate the nanoscale structure with a thin lamella of the order of 100–140 nm produced by focused ion beam (FIB). The neutron data revealed the phase composition of the pellet to be primarily 54(8) wt.% U2CrN3, in good agreement with the stoichiometry of starting reagents (UN and CrN powder) and metallographic analysis. Neutron data analysis confirms that all the crystallographic sites in U2CrN3 phase are fully occupied reinforcing the fully stoichiometric composition of this phase, however, the position of the N at the 4i site was found to be closer to the Cr than previously thought. TEM and selected area electron diffraction rendered nano-level information and revealed the presence of nano domains along grain boundaries of UN and U2CrN3, indicating a formation mechanism of the ternary phase, where the phase likely nucleates as nano domains in UN grains from migration of Cr. © 2023 The Author(s). Published by Elsevier Ltd. Open access article under the CC BY licence.
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    Dopant and current rate dependence on the structural evolution of P2-Na2/3Mn0.8Zn0.1M0.1O2 (M=Cu, Ti): an operando study
    (Wiley, 2021-06-24) Stansby, JH; Sharma, N; Avdeev, M; Brand, HEA; Gonzalo, E; Drewett, NE; Ortiz-Vitoriano, N; Rojo, T
    Variable current rate operando XRD experiments were performed on the P2- Na2/3Mn0.8Zn0.1Cu0.1O2 composition, which displays promising electrochemical properties. The data reveals the reversible formation of a new and previously undetected ordering reflection upon extraction of Na-ions, and that small compositional alterations may dramatically impact structural evolution and electrochemical properties. For P2- Na2/3Mn0.8Zn0.1Cu0.1O2 at all current rates examined (25, 50 and 100 mA.g−1), comparable structural evolution on charge is observed, but the structural evolution on discharge is shown to be significantly influenced by the current applied during the preceding charge step. For both P2- Na2/3Mn0.8Zn0.1Cu0.1O2 and P2- Na2/3Mn0.8Zn0.1Ti0.1O2 comparable structural evolution is observed only at a slower current rate of 25 mA.g−1. Overall, the structural evolution of these layered materials is shown to be dependent on the cycling history, highlighting the significance of applied current rate during cycling, especially during the initial cycle. © 2021 The Authors.
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    P2-Na2/3Mn0.8M0.1M′0.1O2 (M = Zn, Fe and M′ = Cu, Al, Ti): A detailed crystal structure evolution investigation
    (American Chemical Society, 2021-05-24) Stansby, JH; Sharma, N; Avdeev, M; Brand, HEA; Johannessen, B; Gonzalo, E; Drewett, NE; Ortiz-Vitoriano, N; Rojo, T
    Incorporation of various transition metals has been shown to improve the electrochemical performance of Mn-rich Na-ion cathode materials. A greater comprehension of the role of dopant ions, particularly with regard to Mn-rich layered oxides as materials for the positive electrode of Na-ion batteries, is required for their continual development. Here two similar series of Mn-rich P2 cathode materials P2-Na2/3Mn0.8M0.1M′0.1O2 (M = Fe, Zn and M′ = Cu, Al, Ti) are explored, focusing on structural analysis using high-resolution operando synchrotron X-ray diffraction. Notably, under the cycling conditions employed, no P2 to O2 phase transitions toward the charged state were identified for any of the materials investigated. Particularly stable solid solution evolution was observed for P2-Na2/3Mn0.8Zn0.1Cu0.1O2 and P2-Na2/3Mn0.8Zn0.1Al0.1O2 when cycled at 40 mA.g–1 which reflects the electrochemical properties of the materials investigated herein and illustrates that Zn is an excellent choice of dopant for Mn-rich cathode materials. Moreover, the better cyclability of P2-Na2/3Mn0.8Zn0.1Al0.1O2 compared with P2-Na2/3Mn0.8Zn0.1Cu0.1O2 is in keeping with the minimal structural changes observed. This demonstrates that although oxidation state predictions to optimize the initial Mn oxidation state are a good way of initially selecting materials, to truly exploit Mn-rich P2-type materials it is necessary to build up an in-depth understanding of both oxidation states and the associated Jahn–Teller distortion as well as the subtle interplay of synergistic and antagonistic interactions between dopants. Overall, this study illustrates the value of structural investigations to assist in the rational design and validation of novel high-performance materials; the results highlight that the interplay between dopants in addition to the average Mn oxidation state are both crucial considerations when designing high-performance Mn-rich layered oxide materials. © 2021 American Chemical Society