I21-Resonant Inelastic X-ray Scattering (RIXS)
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Diamond Proposal Number(s):
[32023]
Open Access
Abstract: Activation of oxygen anion redox represents an effective method of increasing the specific capacity as well as raising the operating voltage of layered sodium transition metal oxides. However, these reactions are often accompanied by irreversible structural transformations and detrimental side‑reactions between the electrolyte and electrode interface which accelerate degradation, thereby impeding their practical application. To optimise the oxygen anion reversibility for practical use and compare the effects of dopants, we investigated Zn- and Ti-substitution both separately and combined in P3‑structure Na0.7Mn0.75Ni0.25O2, assisted by DFT calculations. The Zn-substituted materials, Na0.7Mn0.65Ni0.25Zn0.1O2 and Na0.7Mn0.58Ni0.25Zn0.07Ti0.1O2 present superior cycling stability over the high voltage range 3.8-4.3 V and enhanced rate capability, delivering a reversible capacity of ~80 mA h g‑1 at 500 mA g‑1 over the voltage window 2.2‑4.3 V compared with 58.6 mA h g-1 for the parent-phase. The improved electrochemical performance of the Zn-substituted materials is attributed to suppression of the P3 to O’3 phase transformation revealed by X‑ray diffraction and the lower electronegativity and filled d ‑band of Zn. The presence of TiO6 octahedra in the Ti-substituted materials relieves structural distortions/TM ordering, also improving the cycling stability. With Zn/Ti co-substitution these advantages may be combined, as demonstrated by the superior electrochemical performance observed for Na0.7Mn0.58Ni0.25Zn0.07Ti0.1O2.
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Jan 2025
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I15-Extreme Conditions
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Ji
Hu
,
Alexander G.
Squires
,
Jędrzej
Kondek
,
Arthur B.
Youd
,
Pooja
Vadhva
,
Michael
Johnson
,
Partha P
Paul
,
Philip J.
Withers
,
Marco
Di Michiel
,
Dean S.
Keeble
,
Michael Ryan
Hansen
,
David O.
Scanlon
,
Alexander J. E.
Rettie
Diamond Proposal Number(s):
[35411]
Open Access
Abstract: Lithium phosphides are an emerging class of Li+ ion conductors for solid state battery applications. Despite potentially favorable characteristics as a solid electrolyte, stoichiometric crystalline Li3AlP2 has been reported to be an ionic insulator. Using a combined computational and experimental approach, we investigate the underlying reasons for this and show that ion transport can be induced via defects and structural disorder in this material. Lithium vacancies are shown to promote diffusion, and a low barrier to Li+ hopping of 0.2-0.3 eV is revealed by both simulations and experiment. However, polycrystalline pellets exhibit low ionic conductivity (≈10−8 S cm−1) at room temperature, attributed to crystalline anisotropy and the presence of resistive grain boundaries. These aspects can be overcome in nanocrystalline Li3AlP2, where ionic conductivity values approaching 10−6 S cm−1 and low electronic conductivities are achieved. This approach, leveraging both defects and structural disorder, should have relevance to the discovery of new, or previously overlooked, ion conducting materials.
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Jan 2025
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I09-Surface and Interface Structural Analysis
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Jiaye
Zhang
,
Zhenni
Yang
,
Siliang
Kuang
,
Ziqi
Zhang
,
Shenglong
Wei
,
Joe
Willis
,
Tien-Lin
Lee
,
Piero
Mazzolini
,
Oliver
Bierwagen
,
Shanquan
Chen
,
Zuhuang
Chen
,
Duanyang
Chen
,
Hongji
Qi
,
David
Scanlon
,
Kelvin H. L.
Zhang
Diamond Proposal Number(s):
[31069, 31681]
Abstract: The bulk and surface electronic structures of Sn-doped 𝛽−Ga2O3 thin films have been studied by soft and hard x-ray photoemission spectroscopy (soft PES at 1486.6 eV and HAXPES at 5920 eV). The experimental spectra are compared with density functional theory calculated density of states in the valence band and conduction band. Excellent agreement was found between experimental spectra and calculated density of states by taking into account the photoionization cross section of different orbitals involved in the valence and conduction bands. The electronic states derived from Ga 4𝑠 character are selectively enhanced by HAXPES. This allows us to infer that the states at the conduction band and bottom of the valence band contain pronounced Ga 4𝑠 character. The occupation of the lower conduction band in degenerately Sn-doped Ga2O3 is clearly observed by HAXPES, which allows for direct measurement of Burstein-Moss shift and band-gap renormalization as a function of Sn doping. A comparison of the valence band spectra of Sn-doped Ga2O3 films with Si-doped samples suggests that Sn doping has different effects on the electronic structure than Si doping. An in-gap electronic state is observed for Sn-doped Ga2O3, which is attributed to self-compensating Sn2+ related defects. Furthermore, a larger band-gap renormalization is found in Sn-doped samples, because the Sn 5𝑠 dopant orbital mixes strongly with the host Ga 4𝑠 derived conduction band. Finally, a comparison of the valence band and core-level spectra excited with soft and hard x rays allows us to identify an upward band bending at the surface region of Sn-doped Ga2O3 films.
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Sep 2024
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James C
Blakesley
,
Ruy Sebastian
Bonilla
,
Marina
Freitag
,
Alex
Ganose
,
Nicola
Gasparini
,
Pascal
Kaienburg
,
George
Koutsourakis
,
Jonathan D.
Major
,
Jenny
Nelson
,
Nakita K.
Noel
,
Bart
Roose
,
Jae Sung
Yun
,
Simon
Aliwell
,
Pietro
Altermatt
,
Tayebeh
Ameri
,
Virgil
Andrei
,
Ardalan
Armin
,
Diego
Bagnis
,
Jenny
Baker
,
Hamish
Beath
,
Mathieu
Bellanger
,
Philippe
Berrouard
,
Jochen
Blumberger
,
Stuart
Boden
,
Hugo
Bronstein
,
Matthew J.
Carnie
,
Chris
Case
,
Fernando A.
Castro
,
Yi-Ming
Chang
,
Elmer
Chao
,
Tracey M.
Clarke
,
Graeme
Cooke
,
Pablo
Docampo
,
Ken
Durose
,
James
Durrant
,
Marina
Filip
,
Richard H.
Friend
,
Jarvist M.
Frost
,
Elizabeth
Gibson
,
Alexander J.
Gillett
,
Pooja
Goddard
,
Severin
Habisreutinger
,
Martin
Heeney
,
Arthur D.
Hendsbee
,
Louise C.
Hirst
,
Saiful
Islam
,
Imalka
Jayawardena
,
Michael
Johnston
,
Matthias
Kauer
,
Jeff
Kettle
,
Ji-Seon
Kim
,
Dan
Lamb
,
David G.
Lidzey
,
Jihoo
Lim
,
Roderick
Mackenzie
,
Nigel
Mason
,
Iain
Mcculloch
,
Keith
Mckenna
,
Sebastian
Meier
,
Paul
Meredith
,
Graham
Morse
,
John
Murphy
,
Chris
Nicklin
,
Paloma
Ortega-Arriaga
,
Thomas
Osterberg
,
Jay
Patel
,
Anthony
Peaker
,
Moritz
Riede
,
Martyn
Rush
,
James
Ryan
,
David O.
Scanlon
,
Peter
Skabara
,
Franky
So
,
Henry J.
Snaith
,
Ludmilla
Steier
,
Jarla
Thiesbrummel
,
Alessandro
Troisi
,
Craig
Underwood
,
Karsten
Walzer
,
Trystan M.
Watson
,
Michael
Walls
,
Aron
Walsh
,
Lucy D.
Whalley
,
Benedict
Winchester
,
Sam
Stranks
,
Robert
Hoye
Open Access
Abstract: Photovoltaics (PVs) are a critical technology for curbing growing levels of anthropogenic greenhouse gas emissions, and meeting increases in future demand for low-carbon electricity. In order to fulfil ambitions for net-zero carbon dioxide equivalent (CO2eq) emissions worldwide, the global cumulative capacity of solar PVs must increase by an order of magnitude from 0.9 TWp in 2021 to 8.5 TWp by 2050 according to the International Renewable Energy Agency, which is considered to be a highly conservative estimate. In 2020, the Henry Royce Institute brought together the UK PV community to discuss the critical technological and infrastructure challenges that need to be overcome to address the vast challenges in accelerating PV deployment. Herein, we examine the key developments in the global community, especially the progress made in the field since this earlier roadmap, bringing together experts primarily from the UK across the breadth of the photovoltaics community. The focus is both on the challenges in improving the efficiency, stability and levelized cost of electricity of current technologies for utility-scale PVs, as well as the fundamental questions in novel technologies that can have a significant impact on emerging markets, such as indoor PVs, space PVs, and agrivoltaics. We discuss challenges in advanced metrology and computational tools, as well as the growing synergies between PVs and solar fuels, and offer a perspective on the environmental sustainability of the PV industry. Through this roadmap, we emphasize promising pathways forward in both the short- and long-term, and for communities working on technologies across a range of maturity levels to learn from each other.
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Aug 2024
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[18786, 25166, 32893]
Open Access
Abstract: The Nb2PdxS5 (x ≈ 0.74) superconductor with a Tc of 6.5 K is reduced by the intercalation of lithium in ammonia solution or electrochemically to produce an intercalated phase with expanded lattice parameters. The structure expands by 2% in volume and maintains the C2/m symmetry and rigidity due to the PdS4 units linking the layers. Experimental and computational analysis of the chemically synthesized bulk sample shows that Li occupies triangular prismatic sites between the layers with an occupancy of 0.33(4). This level of intercalation suppresses the superconductivity, with the injection of electrons into the metallic system observed to also reduce the Pauli paramagnetism by ∼40% as the bands are filled to a Fermi level with a lower density of states than in the host material. Deintercalation using iodine partially restores the superconductivity, albeit at a lower Tc of ∼5.5 K and with a smaller volume fraction than in fresh Nb2PdxS5. Electrochemical intercalation reproduces the chemical intercalation product at low Li content (<0.4) and also enables greater reduction, but at higher Li contents (≥0.4) accessed by this route, phase separation occurs with the indication that Li occupies another site.
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Jan 2024
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Harsh
Bhatia
,
Junjun
Guo
,
Christopher N.
Savory
,
Martyn
Rush
,
David I.
James
,
Avishek
Dey
,
Charles
Chen
,
Dejan-Krešimir
Bučar
,
Tracey M.
Clarke
,
David O.
Scanlon
,
Robert G.
Palgrave
,
Bob C.
Schroeder
Open Access
Abstract: Bismuth-based coordination complexes are advantageous over other metal complexes, as bismuth is the heaviest nontoxic element with high spin–orbit coupling and potential optoelectronics applications. Herein, four bismuth halide-based coordination complexes [Bi2Cl6(phen-thio)2] (1), [Bi2Br6(phen-thio)2] (2), [Bi2I6(phen-thio)2] (3), and [Bi2I6(phen-Me)2] (4) were synthesized, characterized, and subjected to detailed photophysical studies. The complexes were characterized by single-crystal X-ray diffraction, powder X-ray diffraction, and NMR studies. Spectroscopic analyses of 1–4 in solutions of different polarities were performed to understand the role of the organic and inorganic components in determining the ground- and excited-state properties of the complexes. The photophysical properties of the complexes were characterized by ground-state absorption, steady-state photoluminescence, microsecond time-resolved photoluminescence, and absorption spectroscopy. Periodic density functional theory (DFT) calculations were performed on the solid-state structures to understand the role of the organic and inorganic parts of the complexes. The studies showed that changing the ancillary ligand from chlorine (Cl) and bromine (Br) to iodine (I) bathochromically shifts the absorption band along with enhancing the absorption coefficient. Also, changing the halides (Cl, Br to I) affects the photoluminescent quantum yields of the ligand-centered (LC) emissive state without markedly affecting the lifetimes. The combined results confirmed that ground-state properties are strongly influenced by the inorganic part, and the lower-energy excited state is LC. This study paves the way to design novel bismuth coordination complexes for optoelectronic applications by rigorously choosing the ligands and bismuth salt.
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Dec 2023
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Open Access
Abstract: Poly(Ni-btt), an organometallic coordination polymer (OMCP) characterized by the coordination between benzene-1,2,4,5-tetrakis(thiolate) (btt) and Ni2+ ions, has been recognized as a promising p-type thermoelectric material. In this study, we employed a constitutional isomer based on benzene-1,2,3,4-tetrakis(thiolate) (ibtt) to generate the corresponding isomeric polymer, poly(Ni-ibtt). Comparative analysis of poly(Ni-ibtt) and poly(Ni-btt) reveals several common infrared (IR) and Raman features attributed to their similar square-planar nickel-sulfur (Ni-S) coordination. Nevertheless, these two polymer isomers exhibit substantially different backbone geometries. Poly(Ni-btt) possesses a linear backbone, whereas poly(Ni-ibtt) exhibits a more undulating, zigzag-like structure. Consequently, poly(Ni-ibtt) demonstrates slightly higher solubility and an increased bandgap in comparison to poly(Ni-btt). The most noteworthy dissimilarity, however, manifests in their thermoelectric properties. While poly(Ni-btt) exhibits p-type behaviour, poly(Ni-ibtt) demonstrates n-type carrier characteristics. This intriguing divergence prompted further investigation into the influence of OMCP backbone geometry on the electronic structure and, particularly, the thermoelectric properties of these materials.
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Sep 2023
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Open Access
Abstract: Quantifying the crystallographic phases present at a surface is an important challenge in fields such as functional materials and surface science. X-ray photoelectron spectroscopy (XPS) is routinely employed in surface characterization to identify and quantify chemical species through core line analysis. Valence band (VB) spectra contain characteristic but complex features that provide information on the electronic density of states (DoS) and thus can be understood theoretically using density functional theory (DFT). Here, we present a method of fitting experimental photoemission spectra with DFT models for quantitative analysis of heterogeneous systems, specifically mapping the anatase to rutile ratio across the surface of mixed-phase TiO2 thin films. The results were correlated with mapped photocatalytic activity measured using a resazurin-based smart ink. This method allows large-scale functional and surface composition mapping in heterogeneous systems and demonstrates the unique insights gained from DFT-simulated spectra on the electronic structure origins of complex VB spectral features.
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Aug 2023
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[18786, 25166]
Open Access
Abstract: A new reduced phase derived from the excitonic insulator candidate Ta2NiSe5 has been synthesized via the intercalation of lithium. LiTa2NiSe5 crystallizes in the orthorhombic space group Pmnb (no. 62) with lattice parameters a = 3.50247(3) Å, b = 13.4053(4) Å, c = 15.7396(2) Å, and Z = 4, with an increase of the unit cell volume by 5.44(1)% compared with Ta2NiSe5. Significant rearrangement of the Ta-Ni-Se layers is observed, in particular a very significant relative displacement of the layers compared to the parent phase, similar to that which occurs under hydrostatic pressure. Neutron powder diffraction experiments and computational analysis confirm that Li occupies a distorted triangular prismatic site formed by Se atoms of adjacent Ta2NiSe5 layers with an average Li–Se bond length of 2.724(2) Å. Li-NMR experiments show a single Li environment at ambient temperature. Intercalation suppresses the distortion to monoclinic symmetry that occurs in Ta2NiSe5 at 328 K and that is believed to be driven by the formation of an excitonic insulating state. Magnetometry data show that the reduced phase has a smaller net diamagnetic susceptibility than Ta2NiSe5 due to the enhancement of the temperature-independent Pauli paramagnetism caused by the increased density of states at the Fermi level evident also from the calculations, consistent with the injection of electrons during intercalation and formation of a metallic phase.
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Jul 2023
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I09-Surface and Interface Structural Analysis
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Christopher H.
Don
,
Thomas P.
Shalvey
,
Matthew J.
Smiles
,
Luke
Thomas
,
Laurie J.
Phillips
,
Theodore D. C.
Hobson
,
Harry
Finch
,
Leanne A. H.
Jones
,
Jack E. N.
Swallow
,
Nicole
Fleck
,
Christopher
Markwell
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Deepnarayan
Biswas
,
Leon
Bowen
,
Benjamin A. D.
Williamson
,
David O.
Scanlon
,
Vinod R.
Dhanak
,
Ken
Durose
,
Tim D.
Veal
,
Jonathan D.
Major
Diamond Proposal Number(s):
[32696]
Open Access
Abstract: Despite the recent success of CdS/Sb2Se3 heterojunction devices, cadmium toxicity, parasitic absorption from the relatively narrow CdS band gap (2.4 eV) and multiple reports of inter-diffusion at the interface forming Cd(S,Se) and Sb2(S,Se)3 phases, present significant limitations to this device architecture. Among the options for alternative partner layers in antimony chalcogenide solar cells, the wide band gap, non-toxic titanium dioxide (TiO2) has demonstrated the most promise. It is generally accepted that the anatase phase of the polymorphic TiO2 is preferred, although there is currently an absence of analysis with regard to phase influence on device performance. This work reports approaches to distinguish between TiO2 phases using both surface and bulk characterization methods. A device fabricated with a radio frequency (RF) magnetron sputtered rutile-TiO2 window layer (FTO/TiO2/Sb2Se3/P3HT/Au) achieved an efficiency of 6.88% and near-record short–circuit current density (Jsc) of 32.44 mA cm−2, which is comparable to established solution based TiO2 fabrication methods that produced a highly anatase-TiO2 partner layer and a 6.91% efficiency device. The sputtered method introduces reproducibility challenges via the enhancement of interfacial charge barriers in multi-phase TiO2 films with a rutile surface and anatase bulk. This is shown to introduce severe S-shaped current–voltage (J–V) distortion and a drastic fill–factor (FF reduction in these devices.
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Jun 2023
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