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94 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2, 3, 4, 5, 6, 7, 8 [Next/Last]

Instruments / Technical Area	Publication Details	Published
	Anion distribution, structural distortion, and symmetry-driven optical band gap bowing in mixed halide Cs2SnX6 vacancy ordered double perovskites Maham Karim , Alex M. Ganose , Laura Pieters , W. W. Winnie Leung , Jessica Wade , Lina Zhang , David O. Scanlon , Robert G. Palgrave Chemistry Of Materials DOI: 10.1021/acs.chemmater.9b03267 Show Abstract ▼ Abstract: Mixed anion compounds in the Fm-3m vacancy ordered perovskite structure were synthesised and characterised experimentally and computationally with a focus on compounds where A = Cs+. Pure anion Cs2SnX6 compounds were formed with X = Cl, Br and I using a room temperature solution phase method. Mixed anion compounds were formed as solid solutions of Cs2SnCl6 and Cs2SnBr6 and a second series from Cs2SnBr6 and Cs2SnI6. Single phase structures formed across the entirety of both composition series, with no evidence of long range anion ordering observed by diffraction. A distortion of the cubic A2BX6 structure was identified in which the spacing of the BX6 octahedra changes to accommodate the A site cation without reduction of overall symmetry. Optical band gap values varied with anion composition between 4.89 eV in Cs2SnCl6 to 1.35 eV in Cs2SnI6, but proved highly non-linear with changes in composition. In mixed halide compounds it was found that lower energy optical transitions appeared that were not present in the pure halide compounds, and this could be attributed to lowering of the local symmetry within the tin halide octahedra. The electronic structure was characterised by photoemission spectroscopy, and Raman spectroscopy revealed vibrational modes in the mixed halide compounds that could be assigned to particular mixed halide octahedra. This analysis was used to determine the distribution of octahedra types in mixed anion compounds, which was found to be consistent with a near-random distribution of halide anions throughout the structure, although some deviations from random halide distribution were noted in mixed iodide-bromide compounds, where the larger iodide anions preferentially adopted trans configurations.	Nov 2019
I11-High Resolution Powder Diffraction	Computationally-guided discovery of the sulphide Li 3 AlS 3 , in the Li-Al-S phase field: structure and lithium conductivity Jacinthe Gamon , Benjamin B. Duff , Matthew S. Dyer , Christopher Collins , Luke M. Daniels , T. Wesley Surta , Paul M. Sharp , Michael W. Gaultois , Frédéric Blanc , John B. Claridge , Matthew Rosseinsky Chemistry Of Materials DOI: 10.1021/acs.chemmater.9b03230 Show Abstract ▼ Abstract: With the goal of finding new lithium solid electrolytes by a combined computational-experimental method, the exploration of the Li-Al-O-S phase field resulted in the discovery of a new sulphide Li3AlS3. The structure of the new phase was determined through an approach combining synchrotron X-ray and neutron diffraction with 6Li and 27Al magic angle spinning nuclear magnetic resonance spectroscopy, and revealed a highly ordered cationic polyhedral network within a sulphide anion hcp-type sublattice. The originality of the structure relies on the presence of Al2S6 repeating dimer units consisting of two edge-shared Al tetrahedra. We find that, in this structure type consisting of alternating tetrahedral layers with Li-only polyhedra layers, the formation of these dimers is constrained by the Al/S ratio of 1/3. Moreover, by comparing this structure to similar phases such as Li5AlS4 and Li4.4Al0.2Ge0.3S4 ((Al+Ge)/S = 1/4), we discovered that the Al2S6 dimers not only influence atomic displacements and Li polyhedral distortions, but also determine the overall Li polyhedral arrangement within the hcp lattice, leading to the presence of highly ordered vacancies in both the tetrahedral and Li-only layer. AC-impedance measurements revealed a low lithium mobility, which is strongly impacted by the presence of ordered vacancies. Finally, a composition-structure-property relationship understanding was developed to explain the extent of lithium mobility in this structure type.	Oct 2019
I09-Surface and Interface Structural Analysis	Ni 3+ induced hole states enhance the oxygen evolution reaction activity of Ni x Co 3-x O 4 electrocatalysts Meiyan Cui , Xingyu Ding , Xiaochun Huang , Zechao Shen , Tien-lin Lee , Freddy E. Oropeza , Jan P. Hofmann , Emiel J. M. Hensen , Kelvin H. L. Zhang Chemistry Of Materials DOI: 10.1021/acs.chemmater.9b02453 Diamond Proposal Number(s): [21432] Show Abstract ▼ Abstract: This work reports a systematical study on the relationship of electronic structure to oxygen evolution reaction (OER) activity of NixCo3-xO4 (x=0-1) mixed oxides. The specific OER activity is substantially increased by 16 times from 0.02 mA cm-2BET for pure Co3O4 to 0.32 mA cm-2BET for x=1 at an overpotential of 0.4 V and exhibits a strong correlation with the amount of Ni ions in +3 oxidation state. X-ray spectroscopic study reveals that inclusion of Ni3+ ions upshifts the occupied valence band maximum (VBM) by 0.27 eV toward the Fermi level (EF), and creates a new hole (unoccupied) state located ~1 eV above the EF. Such electronic features favour the adsorption of OH surface intermediates on NixCo3-xO4, resulting in enhanced OER. Furthermore, the emerging hole state effectively reduces the energy barrier for electron transfer from 1.19 eV to 0.39 eV, and thereby improves the kinetics for OER. The electronic structure features that lead to a higher OER in NixCo3-xO4 can be extended to other transition metal oxides for rational design of highly active catalysts.	Aug 2019
I20-Scanning-X-ray spectroscopy (XAS/XES)	The unusual redox behaviour of ceria and its interaction with hydrogen Adam H. Clark , Kevin A. Beyer , Shusaku Hayama , Timothy I. Hyde , Gopinathan Sankar Chemistry Of Materials DOI: 10.1021/acs.chemmater.9b02854 Diamond Proposal Number(s): [16508] Show Abstract ▼ Abstract: The reaction between ceria and hydrogen has been subject to numerous theoretical and experimental studies due to its importance as a catalytic material. Here we present dynamic and reversible evolution of the cerium oxidation states observed through X-ray Absorption Spectroscopy experiments in addition to the investigation of associated lattice expansion and contraction through X-ray diffraction and PDF methods. Employing a novel calculation of the temperature dependence of the Gibbs free energy through consideration of the relationship between the instantaneous thermal lattice expansion and the rate of change of the cerium oxidation state, the unusual redox chemistry is reported here. This unusual behaviour is interpreted as due to the formation of a metastable cerium oxyhydride as suggested.	Aug 2019
I09-Surface and Interface Structural Analysis	Selective control of composition in Prussian white for enhanced material properties William R. Brant , Ronnie Mogensen , Simon Colbin , Dickson O. Ojwang , Siegbert Schmid , Lennart Häggström , Tore Ericsson , Aleksander Jaworski , Andrew J. Pell , Reza Younesi Chemistry Of Materials DOI: 10.1021/acs.chemmater.9b01494 Diamond Proposal Number(s): [17901] Show Abstract ▼ Abstract: Sodium ion batteries based on Prussian blue analogues (PBAs) are ideal for large scale energy storage applications due to the ability to meet the huge volumes and low costs required. For Na2-xFe[Fe(CN)6]1-y.zH2O realising its commercial potential means fine control of the concentration of sodium, Fe(CN)6 vacancies and water content. To date, there is a huge variation in the literature of composition leading to variable electrochemical performance. In this work, we break down the synthesis of Prussian blue analogous (PBAs) into three steps for controlling the sodium, vacancy and water content via an inexpen-sive, scalable synthesis method. We produce rhombohedral Prussian white Na1.88(5)Fe[Fe(CN)6].0.18(9)H2O with an initial capacity of 158 mAhg-1 retaining 90% capacity after 50 cycles. Subsequent characterisation revealed that the increased polarisation on the 3 V plateau is coincident with a phase transition and reduced utilisation of the high spin Fe(III)/Fe(II) redox couple. This reveals a clear target for subsequent improvements of the material to boost long term cycling stability. These results will be of great interest for the myriad of applications PBAs are suited towards such as catalysis, magnetism, electrochromics and gas sorption.	Aug 2019
I19-Small Molecule Single Crystal Diffraction	Efficient gas separation and transport mechanism in rare hemilabile metal-organic framework Marta Mon , Rosaria Bruno , Estefanía Tiburcio , Aida Grau-atienza , Antonio Sepulveda-escribano , Enrique V Ramos-fernandez , Alessio Fuoco , Elisa Esposito , Marcello Monteleone , Johannes Carolus Jansen , Joan Cano , Jesus Ferrando-soria , Donatella Armentano , Emilio Pardo Chemistry Of Materials DOI: 10.1021/acs.chemmater.9b01995 Diamond Proposal Number(s): [18768] Show Abstract ▼ Abstract: Understand/visualize the established interactions between gases and adsorbents is mandatory to implement better per-formant materials in adsorption/separation processes. Here we report the unique behavior of a rare example of a hemila-bile chiral three-dimensional metal-organic framework (MOF) with an unprecedented qtz-e-type topology, with formula CuII2(S,S)-hismox . 5H2O (1) (hismox = bis[(S)-histidine]oxalyl diamide). 1 exhibits a continuous and reversible breath-ing behavior, based on the hemilability of carboxylate groups from L-histidine. In-situ powder (PXRD) and single crystal X-ray diffraction (SCXRD) using synchrotron radiation allowed to unveil the crystal structures of 4 different host-guest adsorbates (Ar, N2, CO2 and C3H6@1), the rationalization of the breathing motion and unravel the mechanisms govern-ing the adsorption of these gases. Then, this information has been transferred to implement efficient separations of mix-tures of industrial and environmental relevance –CO2/N2, CO2/CH4 and C3H8/C3H6 using 1 in packed columns as the sta-tionary phase and dispersed in a mixed matrix membrane.	Jul 2019
I09-Surface and Interface Structural Analysis	Degradation mechanisms in Li 2 VO 2 F Li-rich disordered rock-salt cathodes Ida Kallquist , Andrew J. Naylor , Christian Baur , Johann Chable , Jolla Kullgren , Maximilian Fichtner , Kristina Edstrom , Daniel Brandell , Maria Hahlin Chemistry Of Materials DOI: 10.1021/acs.chemmater.9b00829 Diamond Proposal Number(s): [19602] Show Abstract ▼ Abstract: The strive for increased energy density in Li-ion batteries is particularly dependent on the cathode materials, that so far have been limiting for the overall battery performance. A new class of materials, Li-rich disordered rock-salts, has recently been brought forward as promising candidates for next-generation cathodes due to their ability to reversibly cycle more than one Li-ion per transition metal. Several variants of these Li-rich cathode materials have been developed recently and show promising initial capacities, but challenges concerning capacity fade and voltage decay during cycling need yet to be overcome. Mechanisms behind the significant capacity fade of some materials must be understood to allow for the design of new materials in which detrimental reactions can be mitigated. In this study the origin of the capacity fade in the Li-rich material Li2VO2F is investigated and it is shown to begin with a degradation of the particle surface that spreads inwards with continued cycling.	Jun 2019
I11-High Resolution Powder Diffraction	Super-colossal uniaxial negative thermal expansion in chloranilic acid pyrazine, CA-Pyz Huiyu Liu , Matthias J. Gutmann , Harold T. Stokes , Branton J. Campbell , Ivana Radosavljevic Evans , John S. O. Evans Chemistry Of Materials DOI: 10.1021/acs.chemmater.9b01135 Diamond Proposal Number(s): [16297] Show Abstract ▼ Abstract: There has been significant recent interest in exploiting the large dimension changes that can occur in molecular materials as a function of temperature, stress or under optical illumination. Here we report the remarkable thermal expansion properties of chloranilic acid pyrazine (CA-Pyz) co-crystals. We show that the compound shows uniaxial negative thermal expansion over a wide temperature range with a linear contraction coefficient as low as (−)1500×10−6 K−1 at 250 K. The corresponding 10% contraction between 200 and 300 K is an order of magnitude larger than in the so-called colossal contraction materials. We adopt a symmetry-inspired approach to describe both the structural changes that occur (using rotational-symmetry modes) and the thermal expansion (using strain modes). This allows an extremely compact description of the phase transition and detailed understanding of its atomic origins. We show how the coupling of primary and secondary strain modes in materials showing extreme expansion and contraction can lead to unusual reversals in the temperature dependence of cell parameters.	May 2019
B18-Core EXAFS I09-Surface and Interface Structural Analysis	What triggers oxygen loss in oxygen redox cathode materials? Robert A. House , Urmimala Maitra , Liyu Jin , Juan G. Lozano , James W. Somerville , Nicholas H. Rees , Andrew J. Naylor , Laurent C. Duda , Felix Massel , Alan V. Chadwick , Silvia Ramos , David M. Pickup , Daniel E. Mcnally , Xingye Lu , Thorsten Schmitt , Matthew R. Roberts , Peter G. Bruce Chemistry Of Materials DOI: 10.1021/acs.chemmater.9b00227 Diamond Proposal Number(s): [14239, 20870] Show Abstract ▼ Abstract: It is possible to increase the charge capacity of transition metal oxide cathodes in alkali-ion batteries by invoking redox reactions on the oxygen. However, oxygen loss often occurs. To explore what affects oxygen loss in oxygen redox materials, we have compared two analogous Na-ion cathodes, P2-Na0.67Mg0.28Mn0.72O2 and P2-Na0.78Li0.25Mn0.75O2. On charging to 4.5 V, >0.4 e- are removed from the oxide ions of these materials, but neither compound exhibits oxygen loss. Li is retained in P2-Na0.78Li0.25Mn0.75O2 but displaced from the transition metal to the alkali metal layers, showing that vacancies in the transition metal layers, which also occur in other oxygen redox compounds that exhibit oxygen loss such as Li[Li0.2Ni0.2Mn0.6]O2, is not a trigger for oxygen loss. On charging at 5 V, P2-Na0.78Li0.25Mn0.75O2 exhibits oxygen loss whereas P2-Na0.67Mg0.28Mn0.72O2 does not. Under these conditions both Na+ and Li+ are removed from P2-Na0.78Li0.25Mn0.75O2 resulting in underbonded oxygen (fewer than 3 cations coordinating oxygen) and surface localised O loss. In contrast, for P2-Na0.67Mg0.28Mn0.72O2, oxygen remains coordinated by at least 2 Mn4+ and 1 Mg2+ ions, stabilising the oxygen and avoiding oxygen loss.	Apr 2019
I15-1-X-ray Pair Distribution Function (XPDF)	Phase evolution during perovskite formation – insight from pair distribution function analysis Sandy Sanchez , Ullrich Steiner , Xiao Hua Chemistry Of Materials DOI: 10.1021/acs.chemmater.9b00748 Diamond Proposal Number(s): [17315] Show Abstract ▼ Abstract: The recent introduction of organometal halide perovskites to solar cells has significantly enhanced the power conversion efficiency of alternative photovoltaic devices, revolutionizing the development of photovoltaic technologies. To produce perovskite thin films with high device performances, various fabrication methodologies have been developed leading to thin films with different surface structures and crystal morphologies. Tremendous efforts have been devoted to characterizing macro- and microscopic structures within these films to better understand the processing-property-performance relationship. However, their atomic structure and its influence on device performance remains poorly understood. To this end, we employed pair distribution function analysis of X-ray total scattering data to obtain crystallographic and compositional information of methylammonium-lead-iodide (MAPbI3) thin films. This analysis revealed the ubiquitous presence of two near-amorphous intermediate phases with local structures that share subtle but significant correlations with the PbI2 precursor and the desired perovskite phase. The structure transformation from these intermediates to the perovskite deviates from the intuitive belief where the molecular cations get inserted between the sheets of layered PbI2 upon the crystallization of perovskite. This knowledge offers critical insight into the perovskite formation thermodynamics and reveals an important link between the short-range structure of the thin films and their corresponding device performance.	Apr 2019

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