I11-High Resolution Powder Diffraction
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Dingyue
Hu
,
Karl
Dawson
,
Marco
Zanella
,
Troy D.
Manning
,
Luke M.
Daniels
,
Nigel D.
Browning
,
B. Layla
Mehdi
,
Yaobin
Xu
,
Houari
Amari
,
J. Felix
Shin
,
Michael J.
Pitcher
,
Ruiyong
Chen
,
Hongjun
Niu
,
Bowen
Liu
,
Matthew
Bilton
,
Junyoung
Kim
,
John B.
Claridge
,
Matthew J.
Rosseinsky
Diamond Proposal Number(s):
[23666]
Open Access
Abstract: Performance durability is one of the essential requirements for solid oxide fuel cell materials operating in the intermediate temperature range (500–700 °C). The trade-off between desirable catalytic activity and long-term stability challenges the development and commercialization of electrode materials. Here an oxygen cathode material, Ba0.5Sr0.5(Co0.7Fe0.3)0.69−xMgxW0.31O3−δ (BSCFW-xMg), that exhibits excellent electrocatalytic performance through the addition of an optimized amount of Mg to the self-assembled nanocomposite Ba0.5Sr0.5(Co0.7Fe0.3)0.69W0.31O3−δ (BSCFW) by simple solid-state reaction is reported. Distinct from the bulk and surface approaches to introduce vacancies and defects in materials design, here the Mg2+ ions concentrate at the single perovskite/double perovskite interface of BSCFW with dislocations and Mg2+-rich nanolayers, resulting in stressed and compositionally inhomogeneous interface regions. The interfacial chemistry within these nanocomposites provides an additional degree of freedom to enable performance optimization over single phase materials and promotes the durability of alkaline-earth based fuel cell materials.
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Mar 2022
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I11-High Resolution Powder Diffraction
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Harry C.
Sansom
,
Leonardo R. V.
Buizza
,
Marco
Zanella
,
James T.
Gibbon
,
Michael
Pitcher
,
Matthew S.
Dyer
,
Troy D.
Manning
,
Vinod R.
Dhanak
,
Laura M.
Herz
,
Henry J.
Snaith
,
John B.
Claridge
,
Matthew J.
Rosseinsky
Open Access
Abstract: A newly reported compound, CuAgBiI5, is synthesized as powder, crystals, and thin films. The structure consists of a 3D octahedral Ag+/Bi3+ network as in spinel, but occupancy of the tetrahedral interstitials by Cu+ differs from those in spinel. The 3D octahedral network of CuAgBiI5 allows us to identify a relationship between octahedral site occupancy (composition) and octahedral motif (structure) across the whole CuI–AgI–BiI3 phase field, giving the ability to chemically control structural dimensionality. To investigate composition–structure–property relationships, we compare the basic optoelectronic properties of CuAgBiI5 with those of Cu2AgBiI6 (which has a 2D octahedral network) and reveal a surprisingly low sensitivity to the dimensionality of the octahedral network. The absorption onset of CuAgBiI5 (2.02 eV) barely changes compared with that of Cu2AgBiI6 (2.06 eV) indicating no obvious signs of an increase in charge confinement. Such behavior contrasts with that for lead halide perovskites which show clear confinement effects upon lowering dimensionality of the octahedral network from 3D to 2D. Changes in photoluminescence spectra and lifetimes between the two compounds mostly derive from the difference in extrinsic defect densities rather than intrinsic effects. While both materials show good stability, bulk CuAgBiI5 powder samples are found to be more sensitive to degradation under solar irradiation compared to Cu2AgBiI6.
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Nov 2021
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I11-High Resolution Powder Diffraction
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Christopher M.
Collins
,
Luke M.
Daniels
,
Quinn
Gibson
,
Michael W.
Gaultois
,
Michael
Moran
,
Richard
Feetham
,
Michael J.
Pitcher
,
Matthew S
Dyer
,
Charlene
Delacotte
,
Marco
Zanella
,
Claire A.
Murray
,
Gyorgyi
Glodan
,
Olivier
Perez
,
Denis
Pelloquin
,
Troy D.
Manning
,
Jonathan
Alaria
,
George R.
Darling
,
John B.
Claridge
,
Matthew J.
Rosseinsky
Open Access
Abstract: We report the aperiodic titanate Ba 10 Y 6 Ti 4 O 27 with a room temperature thermal conductivity that equals the lowest reported for an oxide. The structure is characterised by discontinuous occupancy modulation of each of the sites, and can be considered as a quasicrystal. The resulting localisation of lattice vibrations suppresses phonon transport of heat. This new lead material for low thermal conductivity oxides is metastable and located within a quaternary phase field that has been previously explored – its isolation thus requires a precisely‐defined synthetic protocol. The necessary narrowing of the search space for experimental investigation is achieved by evaluation of titanate crystal chemistry, prediction of unexplored structural motifs that will favour synthetically accessible new compositions and assessment of their properties with machine learning models.
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May 2021
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I15-1-X-ray Pair Distribution Function (XPDF)
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Abstract: The La1+xAE1–xGa3O7+x/2 melilite family (AE = Ca, Sr, and Ba and 0 ≤ x ≤ 0.64) demonstrates remarkable oxide ion conductivity due to the ability of its layered tetrahedral [Ga3O7+x/2] network to accommodate and transport interstitial oxide ions (Oint). Compositions of x > 0.65 with very high Oint concentrations (referred to here as “super-excess” compositions) have the potential to support correspondingly high ionic conductivities but have never before been accessed due to the limitations of conventional solid-state ceramic synthesis. Here, we report that fully substituted La2Ga3O7.5 (x = 1) melilite ceramics can be synthesized by direct crystallization of an under-cooled melt, demonstrating that super-excess compositions are accessible under suitable nonequilibrium reaction conditions. La2Ga3O7.5 is stable up to 830 °C and exhibits an ionic conductivity of 0.01 S·cm–1 at 800 °C, 3 orders of magnitude higher than the corresponding x = 0 end-member LaSrGa3O7 and close to the range exhibited by the current best-in-class La1.54Sr0.46Ga3O7.23 (0.1 S·cm–1). It crystallizes in an orthorhombic √2a × √2a × 2c expansion of the parent melilite cell in the space group Ima2 with full long-range ordering of Oint into chains within the [Ga3O7.5] layers. The emergence of this chain-like (1D) ordering within the 2D melilite framework, which appears to be an incipient feature of previously reported partially ordered melilites, is explained in terms of the underlying hexagonal topology of the structure. These results will enable the exploration of extended compositional ranges for the development of new solid oxide ion electrolytes with high concentrations of interstitial oxide charge carriers.
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Oct 2020
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B18-Core EXAFS
I11-High Resolution Powder Diffraction
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Zoe N.
Taylor
,
Arnaud J.
Perez
,
Jose A.
Coca-Clemente
,
Filipe
Braga
,
Nicholas E.
Drewett
,
Michael J.
Pitcher
,
William J.
Thomas
,
Matthew S.
Dyer
,
Christopher
Collins
,
Marco
Zanella
,
Timothy
Johnson
,
Sarah
Day
,
Chiu
Tang
,
Vinod R
Dhanak
,
John B.
Claridge
,
Laurence J.
Hardwick
,
Matthew J.
Rosseinsky
Abstract: Multinary lithium oxides with the rock salt structure are of technological importance as cathode materials in rechargeable lithium ion batteries. Current state of the art cathodes such as LiNi1/3Mn1/3Co1/3O2 rely on redox cycling of earth-abundant transition metal cations to provide charge capacity. Recently, the possibility of using the oxide anion as a redox center in Li-rich rock salt oxides has been established as a new paradigm in the design of cathode materials with enhanced capacities (> 200 mAh/g). To increase the lithium content and access electrons from oxygen-derived states, these materials typically require transition metals in high oxidation states, which can be easily achieved using d0 cations. However, Li-rich rocksalt oxides with high valent d0 cations such as Nb5+ and Mo6+ show strikingly high voltage hysteresis between charge and discharge, the origin of which is uninvestigated. In this work, we study a series of Li-rich compounds, Li4+xNi1-xWO6 (0 ≤ x ≤ 0.25), adopting two new and distinct cation-ordered variants of the rock salt structure. The phase Li4.15Ni0.85WO6 (x = 0.15) has a large reversible capacity of 200 mAh/g, without accessing the Ni3+/Ni4+ redox couple, implying that over two-thirds of the capacity is due to anionic redox, with good cyclability. The presence of the 5d0 W6+ cation affords extensive (> 2 V) voltage hysteresis associated with the anionic redox. We present experimental evidence for the formation of strongly stabilized localized O-O single bonds that explain the energy penalty required to reduce the material upon discharge. The high valent d0 cation associates localized anion-anion bonding with the anion redox capacity.
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Apr 2019
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I11-High Resolution Powder Diffraction
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Simon J.
Cassidy
,
Michael J.
Pitcher
,
Jared J. K.
Lim
,
Joke
Hadermann
,
Jeremy P.
Allen
,
Graeme W.
Watson
,
Sylvia
Britto
,
Elena J.
Chong
,
David G.
Free
,
Clare P.
Grey
,
Simon J.
Clarke
Diamond Proposal Number(s):
[13284, 18786]
Open Access
Abstract: The chemical accessibility of the CeIV oxidation state enables redox chemistry to be performed on the naturally coinage-metal-deficient phases CeM1–xSO (M = Cu, Ag). A metastable black compound with the PbFCl structure type (space group P4/nmm: a = 3.8396(1) Å, c = 6.607(4) Å, V = 97.40(6) Å3) and a composition approaching CeSO is obtained by deintercalation of Ag from CeAg0.8SO. High-resolution transmission electron microscopy reveals the presence of large defect-free regions in CeSO, but stacking faults are also evident which can be incorporated into a quantitative model to account for the severe peak anisotropy evident in all the high-resolution X-ray and neutron diffractograms of bulk CeSO samples; these suggest that a few percent of residual Ag remains. A straw-colored compound with the filled PbFCl (i.e., ZrSiCuAs- or HfCuSi2-type) structure (space group P4/nmm: a = 3.98171(1) Å, c = 8.70913(5) Å, V = 138.075(1) Å3) and a composition close to LiCeSO, but with small amounts of residual Ag, is obtained by direct reductive lithiation of CeAg0.8SO or by insertion of Li into CeSO using chemical or electrochemical means. Computation of the band structure of pure, stoichiometric CeSO predicts it to be a Ce4+ compound with the 4f-states lying approximately 1 eV above the sulfide-dominated valence band maximum. Accordingly, the effective magnetic moment per Ce ion measured in the CeSO samples is much reduced from the value found for the Ce3+-containing LiCeSO, and the residual paramagnetism corresponds to the Ce3+ ions remaining due to the presence of residual Ag, which presumably reflects the difficulty of stabilizing Ce4+ in the presence of sulfide (S2–). Comparison of the behavior of CeCu0.8SO with that of CeAg0.8SO reveals much slower reaction kinetics associated with the Cu1–xS layers, and this enables intermediate CeCu1–xLixSO phases to be isolated.
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Feb 2019
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I19-Small Molecule Single Crystal Diffraction
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C.
Delacotte
,
G. F. S.
Whitehead
,
M. J.
Pitcher
,
C. M
Robertson
,
P. M.
Sharp
,
M. S.
Dyer
,
Jo.
Alaria
,
J. B.
Claridge
,
G. R.
Darling
,
D. R.
Allan
,
G.
Winter
,
M. J.
Rosseinsky
Diamond Proposal Number(s):
[15777]
Open Access
Abstract: Hexaferrites are an important class of magnetic oxides with applications in data storage and electronics. Their crystal structures are highly modular, consisting of Fe- or Ba-rich close-packed blocks that can be stacked in different sequences to form a multitude of unique structures, producing large anisotropic unit cells with lattice parameters typically >100 Å along the stacking axis. This has limited atomic-resolution structure solutions to relatively simple examples such as Ba2Zn2Fe12O22, whilst longer stacking sequences have been modelled only in terms of block sequences, with no refinement of individual atomic coordinates or occupancies. This paper describes the growth of a series of complex hexaferrite crystals, their atomic-level structure solution by high-resolution synchrotron X-ray diffraction, electron diffraction and imaging methods, and their physical characterization by magnetometry. The structures include a new hexaferrite stacking sequence, with the longest lattice parameter of any hexaferrite with a fully determined structure.
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Nov 2018
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I11-High Resolution Powder Diffraction
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Abstract: We present the synthesis and characterization of the K+ intercalated rubrene (C42H28) phase, K2Rubrene (K2R) and identify the co-existence of amorphous and crystalline materials in samples where the crystalline component is phase pure. We suggest this is characteristic of many intercalated alkali metal-polyaromatic hydrocarbon (PAH) systems, including those for which superconductivity has been claimed. The systematic investigation of K-rubrene solid state reactions using both K and KH sources reveals complex competition between K intercalation and the decomposition of rubrene, producing three K-intercalated compounds, namely, K2R, K(RR*), and KxRʹ (where R* and Rʹ are rubrene decomposition derivatives C42H26 and C30H20, respectively). K2R is obtained as the major phase over a wide composition range and is accompanied by the formation of amorphous by-products from the decomposition of rubrene. K(RR*) is synthesized as a single phase and KxRʹ is obtained only as a secondary phase to the majority K2R phase. The crystal structure of K2R was determined using high resolution powder X-ray diffraction, revealing that the structural rearrangement from pristine rubrene creates two large voids per rubrene within the molecular layers in which K+ is incorporated. K+ cations accommodated within the large voids interact strongly with the neighbouring rubrene via η6, η3 and η2 binding modes to the tetracene cores and the phenyl groups. This contrasts with other intercalated PAHs where only a single void per PAH is created and the intercalated K+ weakly interact with the host. The decomposition products of rubrene are also examined using solution NMR, highlighting the role of the breaking of C-CPhenyl bonds. For the crystalline decomposition derivative products K(RR*) and KxRʹ, a lack of definitive structural information with regards to R* and Rʹ prevents the crystal structures being determined. The study illustrates the complexity in accessing solvent-free alkali metal salts of reduced PAH of the type claimed to afford superconductivity.
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Nov 2018
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I11-High Resolution Powder Diffraction
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Bernhard T.
Leube
,
Kenneth K.
Inglis
,
Elliot
Carrington
,
Paul M.
Sharp
,
J. Felix
Shin
,
Alex R.
Neale
,
Troy D.
Manning
,
Michael J.
Pitcher
,
Laurence
Hardwick
,
Matthew S.
Dyer
,
Frédéric
Blanc
,
John B.
Claridge
,
Matthew J.
Rosseinsky
Open Access
Abstract: In order to understand the structural and compositional factors controlling lithium transport in sulfides, we explored the Li5AlS4 – Li4GeS4 phase field for new materials. Both parent compounds are defined structurally by a hexagonal close packed sulfide lattice, where distinct arrangements of tetrahedral metal sites give Li5AlS4 a layered structure and Li4GeS4 a three dimensional structure related to γ-Li3PO4. The combination of the two distinct structural motifs is expected to lead to new structural chemistry. We identified the new crystalline phase Li4.4Al0.4Ge0.6S4, and investigated the structure and Li+ ion dynamics of the family of structurally related materials Li4.4M0.4M’0.6S4 (M = Al3+, Ga3+ and M’= Ge4+, Sn4+). We used neutron diffraction to solve the full structures of the Al-homologues, which adopt a layered close-packed structure with a new arrangement of tetrahedral (M/M’) sites and a novel combination of ordered and disordered lithium vacancies. AC impedance spectroscopy revealed lithium conductivities in the range 3(2) x 10-6 to 4.3(3) x 10-5 S cm-1 at room temperature with activation energies between 0.43(1) and 0.38(1) eV. Electrochemical performance was tested in a plating and stripping experiment against Li metal electrodes and showed good stability of the Li4.4Al0.4Ge0.6S4 phase over 200 hours. A combination of variable temperature 7Li solid state nuclear magnetic resonance spectroscopy and ab initio molecular dynamics calculations on selected phases showed that two dimensional diffusion with a low energy barrier of 0.17 eV is responsible for long-range lithium transport, with diffusion pathways mediated by the disordered vacancies while the ordered vacancies do not contribute to the conductivity. This new structural family of sulfide Li+ ion conductors offers insight into the role of disordered vacancies on Li+ ion conductivity mechanisms in hexagonally close packed sulfides that can inform future materials design.
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Sep 2018
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I11-High Resolution Powder Diffraction
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Christos A.
Tzitzeklis
,
Jyoti K.
Gupta
,
Matthew S.
Dyer
,
Troy D.
Manning
,
Michael J.
Pitcher
,
Hongjun J.
Niu
,
Stanislav
Savvin
,
Jonathan
Alaria
,
George R.
Darling
,
John B.
Claridge
,
Matthew J.
Rosseinsky
Diamond Proposal Number(s):
[12336]
Abstract: It is challenging to achieve p-type doping of zinc oxides (ZnO), which are of interest as transparent conductors in optoelectronics. A ZnO-related ternary compound, SrZnO2, was investigated as a potential host for p-type conductivity. First-principles investigations were used to select from a range of candidate dopants the substitution of Li+ for Zn2+ as a stable, potentially p-type, doping mechanism in SrZnO2. Subsequently, single-phase bulk samples of a new p-type-doped oxide, SrZn1–xLixO2 (0 < x < 0.06), were prepared. The structural, compositional, and physical properties of both the parent SrZnO2 and SrZn1–xLixO2 were experimentally verified. The band gap of SrZnO2 was calculated using HSE06 at 3.80 eV and experimentally measured at 4.27 eV, which confirmed the optical transparency of the material. Powder X-ray diffraction and inductively coupled plasma analysis were combined to show that single-phase ceramic samples can be accessed in the compositional range x < 0.06. A positive Seebeck coefficient of 353(4) μV K–1 for SrZn1–xLixO2, where x = 0.021, confirmed that the compound is a p-type conductor, which is consistent with the pO2 dependence of the electrical conductivity observed in all SrZn1–xLixO2 samples. The conductivity of SrZn1–xLixO2 is up to 15 times greater than that of undoped SrZnO2 (for x = 0.028 σ = 2.53 μS cm–1 at 600 °C and 1 atm of O2).
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Sep 2018
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