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134 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
	Crystal structure of colloidally prepared metastable Ag2Se nanocrystals Bryce A. Tappan , Bonan Zhu , Patrick Cottingham , Matthew Mecklenburg , David O. Scanlon , Richard L. Brutchey Nano Letters DOI: 10.1021/acs.nanolett.1c02045 Show Abstract ▼ Abstract: Structural polymorphism is known for many bulk materials; however, on the nanoscale metastable polymorphs tend to form more readily than in the bulk, and with more structural variety. One such metastable polymorph observed for colloidal Ag2Se nanocrystals has traditionally been referred to as the “tetragonal” phase. While there are reports on the chemistry and properties of this metastable polymorph, its crystal structure, and therefore electronic structure, has yet to be determined. We report that an anti-PbCl2-like structure type (space group P21/n) more accurately describes the powder X-ray diffraction and X-ray total scattering patterns of colloidal Ag2Se nanocrystals prepared by several different methods. Density functional theory (DFT) calculations indicate that this anti-PbCl2-like Ag2Se polymorph is a dynamically stable, narrow-band-gap semiconductor. The anti-PbCl2-like structure of Ag2Se is a low-lying metastable polymorph at 5–25 meV/atom above the ground state, depending on the exchange-correlation functional used.	Jul 2021
I09-Surface and Interface Structural Analysis	Electrochemical oxidative fluorination of an oxide perovskite Nicholas H. Bashian , Mateusz Zuba , Ahamed Irshad , Shona M. Becwar , Julija Vinckeviciute , Warda Rahim , Kent J. Griffith , Eric T. Mcclure , Joseph K. Papp , Bryan D. Mccloskey , David O. Scanlon , Bradley F. Chmelka , Anton Van Der Ven , Sri R. Narayan , Louis F. J. Piper , Brent Melot Chemistry Of Materials DOI: 10.1021/acs.chemmater.1c01594 Diamond Proposal Number(s): [22250] Show Abstract ▼ Abstract: We report on the electrochemical fluorination of the A-site vacant perovskite ReO3 using high-temperature solid-state cells as well as room-temperature liquid electrolytes. Using galvanostatic oxidation and electrochemical impedance spectroscopy, we find that ReO3 can be oxidized by approximately 0.5 equiv of electrons when in contact with fluoride-rich electrolytes. Results from our density functional theory calculations clearly rule out the most intuitive mechanism for charge compensation, whereby F-ions would simply insert onto the A-site of the perovskite structure. Operando X-ray diffraction, neutron total scattering measurements, X-ray spectroscopy, and solid-state 19F NMR with magic-angle spinning were, therefore, used to explore the mechanism by which fluoride ions react with the ReO3 electrode during oxidation. Taken together, our results indicate that a complex structural transformation occurs following fluorination to stabilize the resulting material. While we find that this process of fluorinating ReO3 appears to be only partially reversible, this work demonstrates a practical electrolyte and cell design that can be used to evaluate the mobility of small anions like fluoride that is robust at room temperature and opens new opportunities for exploring the electrochemical fluorination of many new materials.	Jul 2021
	Surfaxe: Systematic surface calculations Katarina Brlec , Daniel Davies , David O. Scanlon Journal Of Open Source Software 6 DOI: 10.21105/joss.03171 Open Access Show Abstract ▼ Abstract: Surface science is key to understanding the properties of a wide range of materials for energy applications, from catalysts to solar cells to battery components. Computational modelling based on quantum mechanics is often used to calculate surface properties of materials, which in turn determine their stability and performance. The maturity of these “first-principles” methods, coupled with the huge amount of computational power accessible today, means they can now be used predictively in high-throughput screening workflows to suggest new materials for specific applications before they are synthesised. The surfaxe package provides a framework for such screening workflows, automating each stage of the process.	May 2021
	Experimental and theoretical study of the electronic structures of lanthanide indium perovskites LnInO3 P. Hartley , R. G. Egdell , K. H. L. Zhang , M. V. Hohmann , L. F. J. Piper , D. J. Morgan , D. O. Scanlon , B. A. D. Williamson , A. Regoutz The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.0c11592 Open Access Show Abstract ▼ Abstract: Ternary lanthanide indium oxides LnInO3 (Ln = La, Pr, Nd, Sm) were synthesized by high-temperature solid-state reaction and characterized by X-ray powder diffraction. Rietveld refinement of the powder patterns showed the LnInO3 materials to be orthorhombic perovskites belonging to the space group Pnma, based on almost-regular InO6 octahedra and highly distorted LnO12 polyhedra. Experimental structural data were compared with results from density functional theory (DFT) calculations employing a hybrid Hamiltonian. Valence region X-ray photoelectron and K-shell X-ray emission and absorption spectra of the LnInO3 compounds were simulated with the aid of the DFT calculations. Photoionization of lanthanide 4f orbitals gives rise to a complex final-state multiplet structure in the valence region for the 4fn compounds PrInO3, NdInO3, and SmInO3, and the overall photoemission spectral profiles were shown to be a superposition of final-state 4fn–1 terms onto the cross-section weighted partial densities of states from the other orbitals. The occupied 4f states are stabilized in moving across the series Pr–Nd–Sm. Band gaps were measured using diffuse reflectance spectroscopy. These results demonstrated that the band gap of LaInO3 is 4.32 eV, in agreement with DFT calculations. This is significantly larger than a band gap of 2.2 eV first proposed in 1967 and based on the idea that In 4d states lie above the top of the O 2p valence band. However, both DFT and X-ray spectroscopy show that In 4d is a shallow core level located well below the bottom of the valence band. Band gaps greater than 4 eV were observed for NdInO3 and SmInO3, but a lower gap of 3.6 eV for PrInO3 was shown to arise from the occupied Pr 4f states lying above the main O 2p valence band.	Mar 2021
	Rapid recombination by cadmium vacancies in CdTe Seán R. Kavanagh , Aron Walsh , David O. Scanlon Acs Energy Letters 6, 1392 - 1398 DOI: 10.1021/acsenergylett.1c00380 Open Access Show Abstract ▼ Abstract: CdTe is currently the largest thin-film photovoltaic technology. Non-radiative electron–hole recombination reduces the solar conversion efficiency from an ideal value of 32% to a current champion performance of 22%. The cadmium vacancy (VCd) is a prominent acceptor species in p-type CdTe; however, debate continues regarding its structural and electronic behavior. Using ab initio defect techniques, we calculate a negative-U double-acceptor level for VCd, while reproducing the VCd1– hole–polaron, reconciling theoretical predictions with experimental observations. We find the cadmium vacancy facilitates rapid charge-carrier recombination, reducing maximum power-conversion efficiency by over 5% for untreated CdTe—a consequence of tellurium dimerization, metastable structural arrangements, and anharmonic potential energy surfaces for carrier capture.	Mar 2021
	Accelerating the development of new solar absorbers by photoemission characterization coupled with density functional theory Tim D. Veal , David O. Scanlon , Robert Kostecki , Elisabetta Arca Journal Of Physics: Energy 3 DOI: 10.1088/2515-7655/abebc9 Open Access Show Abstract ▼ Abstract: The expectation to progress towards Terawatts production by solar technologies requires continuous development of new materials to improve efficiency and lower the cost of devices beyond what is currently available at industrial level. At the same time, the turnaround time to make the investment worthwhile is progressively shrinking. Whereas traditional absorbers have developed in a timeframe spanning decades, there is an expectation that emerging materials will be converted into industrially relevant reality in a much shorter timeframe. Thus, it becomes necessary to develop new approaches and techniques that could accelerate decision-making steps on whether further research on a material is worth pursuing or not. In this review, we will provide an overview of the photoemission characterization methods and theoretical approaches that have been developed in the past decades to accelerate the transfer of emerging solar absorbers into efficient devices.	Mar 2021
	Surface engineering strategy using urea to improve the rate performance of Na2Ti3O7 in Na‐ion batteries Sara I. R. Costa , Yong‐seok Choi , Alistair J. Fielding , Andrew J. Naylor , John M. Griffin , Zdeněk Sofer , David O. Scanlon , Nuria Tapia-Ruiz Chemistry – A European Journal 27, 3875 - 3886 DOI: 10.1002/chem.v27.11 Open Access Show Abstract ▼ Abstract: Na2Ti3O7 (NTO) is considered a promising anode material for Na‐ion batteries due to its layered structure with an open framework and low and safe average operating voltage of 0.3 V vs. Na+/Na. However, its poor electronic conductivity needs to be addressed to make this material attractive for practical applications among other anode choices. Here, we report a safe, controllable and affordable method using urea that significantly improves the rate performance of NTO by producing surface defects such as oxygen vacancies and hydroxyl groups, and the secondary phase Na2Ti6O13. The enhanced electrochemical performance agrees with the higher Na+ ion diffusion coefficient, higher charge carrier density and reduced bandgap observed in these samples, without the need of nanosizing and/or complex synthetic strategies. A comprehensive study using a combination of diffraction, microscopic, spectroscopic and electrochemical techniques supported by computational studies based on DFT calculations, was carried out to understand the effects of this treatment on the surface, chemistry and electronic and charge storage properties of NTO. This study underscores the benefits of using urea as a strategy for enhancing the charge storage properties of NTO and thus, unfolding the potential of this material in practical energy storage applications.	Feb 2021
	Formation and migration of vacancy defects in GeSe and SnSe Sa Zhang , Meng Lu Li , Ming Jiang , Haiyan Xiao , David O. Scanlon , Xiaotao Zu Journal Of Physics B: Atomic, Molecular And Optical Physics DOI: 10.1088/1361-6455/abd9fd Show Abstract ▼ Abstract: The GeSe and SnSe have great potential in nuclear detector devices. Under irradiation, the formation and migration of point defects may affect their properties and performance significantly. In this study, a comparative study of vacancy formation and migration in GeSe and SnSe has been carried out by a first-principles method. It is shown that in both compounds the cation vacancies are generally much easier to form than anion vacancies, and the cation vacancies are generally easier to migrate than anion vacancies. For both Ge vacancy and Sn vacancy, the migration is anisotropic and the [322] direction is the most favorable migration pathway. The migration energy barrier are 0.54 eV for Ge vacancy and 0.46–0.52 eV for Sn vacancy, suggesting that vacancy clusters are relatively easy to form in both compounds, which may influence the application of GeSe and SnSe in nuclear detector devices.	Jan 2021
	Extending the performance limit of anodes: Insights from diffusion kinetics of alloying anodes Yong‐seok Choi , David O. Scanlon , Jae‐chul Lee Advanced Energy Materials 3 DOI: 10.1002/aenm.202003078 Show Abstract ▼ Abstract: Alloying anodes have long attracted attention as promising candidate electrodes for application in grid‐level energy storage systems owing to their high energy capacity. Alloying anode‐based batteries, however, remain far from practical applications, which require several issues affecting cell performance to be addressed. The large volumetric expansion of anodes and associated phenomena that occur during battery cycling are the main reasons for the poor electrochemical performance of alloying anodes. These electrochemical behaviors of alloying anodes originate from the reactions between the unreacted anode material and inflowing carrier ions. Thus, the diffusion kinetics play a key role in determining the electrochemical properties of alloying anodes. Recent advances in analytical instruments and atomic simulations offer new approaches for interpreting anode performance. Beginning with a brief historical background, this review presents an overview of the origin of diffusion kinetics and how this concept has been extended to alloying anodes. Accordingly, the relationship between the diffusion kinetics and electrochemical performance of alloying anodes is discussed, combined with efficient strategies that can be adopted to improve electrochemical properties. Finally, a design overview of next‐generation alloying anodes that can extend the batteries’ performance limit is proposed.	Dec 2020
	Geometric analysis and formability of the cubic A2BX6 vacancy-ordered double perovskite structure Warda Rahim , Anjie Cheng , Chenyang Lyu , Tianyi Shi , Ziheng Wang , David O. Scanlon , Robert G. Palgrave Chemistry Of Materials DOI: 10.1021/acs.chemmater.0c02806 Show Abstract ▼ Abstract: A geometric analysis of the cubic A2BX6 structure commonly formed by metal halides is presented. Using the “hard-sphere” approximation, where the ions are represented by spheres of a fixed radius, we derive four limiting models that each constrain the distances between constituent ions in different ways. We compare the lattice parameters predicted by these four models with experimental data from the Inorganic Crystal Structure Database (ICSD). For the fluorides, the maintenance of the AX bond length at the sum of the A and X radii gives the best approximation of the lattice parameter, leading to structures with widely separated BX6 octahedra. For the heavier halides, a balance between forming an A-site cavity of the correct size and maintaining suitable anion–anion distances determines the lattice parameter. It is found that in many A2BX6 compounds of heavier halides, the neighboring octahedra show very significant anion–anion overlap. We use these models to predict a compound with A-site rattling and use density functional theory (DFT) to confirm this prediction. Finally, we use the geometric models to derive formability criteria for vacancy-ordered double perovskites.	Nov 2020

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