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145 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
I06-Nanoscience	Manipulating the metal-to-insulator transition and magnetic properties in manganite thin films via epitaxial strain Dong Li , Bonan Zhu , Dirk Backes , Larissa S. I. Veiga , Tien-Lin Lee , Hongguang Wang , Qian He , Pinku Roy , Jiaye Zhang , Jueli Shi , Aiping Chen , Peter A. Van Aken , Quanxi Jia , Sarnjeet S. Dhesi , David O. Scanlon , Kelvin H. L. Zhang , Weiwei Li Physical Review B 105 DOI: 10.1103/PhysRevB.105.165426 Diamond Proposal Number(s): [25425, 26901, 29616] Show Abstract ▼ Abstract: Strain engineering of epitaxial transition metal oxide heterostructures offers an intriguing opportunity to control electronic structures by modifying the interplay between spin, charge, orbital, and lattice degrees of freedom. Here, we demonstrate that the electronic structure, magnetic and transport properties of La 0.9 Ba 0.1 MnO 3 thin films can be effectively controlled by epitaxial strain. Spectroscopic studies and first-principles calculations reveal that the orbital occupancy in Mn e g orbitals can be switched from the d 3 z 2 − r 2 orbital to the d x 2 − y 2 orbital by varying the strain from compressive to tensile. The change of orbital occupancy associated with Mn 3 d -O 2 p hybridization leads to dramatic modulation of the magnetic and electronic properties of strained La 0.9 Ba 0.1 MnO 3 thin films. Under moderate tensile strain, an emergent ferromagnetic insulating state with an enhanced ferromagnetic Curie temperature of 215 K is achieved. These findings not only deepen our understanding of electronic structures, magnetic and transport properties in the La 0.9 Ba 0.1 MnO 3 system, but also demonstrate the use of epitaxial strain as an effective knob to tune the electronic structures and related physical properties for potential spintronic device applications.	Apr 2022
I09-Surface and Interface Structural Analysis	Deep UV transparent conductive oxide thin films realized through degenerately doped wide-bandgap gallium oxide Jiaye Zhang , Joe Willis , Zhenni Yang , Xu Lian , Wei Chen , Lai-Sen Wang , Xiangyu Xu , Tien-Lin Lee , Lang Chen , David O. Scanlon , Kelvin H. I. Zhang Cell Reports Physical Science 6 DOI: 10.1016/j.xcrp.2022.100801 Diamond Proposal Number(s): [24219] Open Access Show Abstract ▼ Abstract: Deep UV transparent thin films have recently attracted considerable attention owing to their potential in UV and organic-based optoelectronics. Here, we report the achievement of a deep UV transparent and highly conductive thin film based on Si-doped Ga2O3 (SGO) with high conductivity of 2500 S/cm. The SGO thin films exhibit high transparency over a wide spectrum ranging from visible light to deep UV wavelength and, meanwhile, have a very low work-function of approximately 3.2 eV. A combination of photoemission spectroscopy and theoretical studies reveals that the delocalized conduction band derived from Ga 4s orbitals is responsible for the Ga2O3 films’ high conductivity. Furthermore, Si is shown to act as an efficient shallow donor, yielding high mobility up to approximately 60 cm2/Vs. The superior optoelectronic properties of SGO films make it a promising material for use as electrodes in high-power electronics and deep UV and organic-based optoelectronic devices.	Mar 2022
I09-Surface and Interface Structural Analysis	Modulation of the Bi3+ 6S2 lone pair state in perovskites for high-mobility p-type oxide semiconductors Jueli Shi , Ethan A. Rubinstein , Weiwei Li , Jiaye Zhang , Ye Yang , Tien-Lin Lee , Changdong Qin , Pengfei Yan , Judith L. Macmanus-Driscoll , David O. Scanlon , Kelvin H.l. Zhang Advanced Science DOI: 10.1002/advs.202104141 Diamond Proposal Number(s): [24219] Open Access Show Abstract ▼ Abstract: Oxide semiconductors are key materials in many technologies from flat-panel displays，solar cells to transparent electronics. However, many potential applications are hindered by the lack of high mobility p-type oxide semiconductors due to the localized O-2p derived valence band (VB) structure. In this work, the VB structure modulation is reported for perovskite Ba2BiMO6 (M = Bi, Nb, Ta) via the Bi 6s2 lone pair state to achieve p-type oxide semiconductors with high hole mobility up to 21 cm2 V−1 s−1, and optical bandgaps widely varying from 1.5 to 3.2 eV. Pulsed laser deposition is used to grow high quality epitaxial thin films. Synergistic combination of hard x-ray photoemission, x-ray absorption spectroscopies, and density functional theory calculations are used to gain insight into the electronic structure of Ba2BiMO6. The high mobility is attributed to the highly dispersive VB edges contributed from the strong coupling of Bi 6s with O 2p at the top of VB that lead to low hole effective masses (0.4–0.7 me). Large variation in bandgaps results from the change in the energy positions of unoccupied Bi 6s orbital or Nb/Ta d orbitals that form the bottom of conduction band. P–N junction diode constructed with p-type Ba2BiTaO6 and n-type Nb doped SrTiO3 exhibits high rectifying ratio of 1.3 × 104 at ±3 V, showing great potential in fabricating high-quality devices. This work provides deep insight into the electronic structure of Bi3+ based perovskites and guides the development of new p-type oxide semiconductors.	Jan 2022
	Predicting lithium iron oxysulfides for battery cathodes Bonan Zhu , David O. Scanlon Acs Applied Energy Materials DOI: 10.1021/acsaem.1c03094 Show Abstract ▼ Abstract: Cathode materials that have high specific energies and low manufacturing costs are vital for the scaling up of lithium-ion batteries (LIBs) as energy storage solutions. Fe-based intercalation cathodes are highly attractive because of the low cost and the abundance of raw materials. However, existing Fe-based materials, such as LiFePO4, suffer from low capacity due to the large size of the polyanions. Turning to mixed anion systems can be a promising strategy to achieve higher specific capacity. Recently, antiperovskite-structured oxysulfide Li2FeSO has been synthesized and reported to be electrochemically active. In this work, we perform an extensive computational search for iron-based oxysulfides using ab initio random structure searching (AIRSS). By performing an unbiased sampling of the Li–Fe–S–O chemical space, several oxysulfide phases have been discovered, which are predicted to be less than 50 meV/atom from the convex hull and potentially accessible for synthesis. Among the predicted phases, two anti-Ruddlesden–Popper-structured materials Li2Fe2S2O and Li4Fe3S3O2 have been found to be attractive as they have high theoretical capacities with calculated average voltages of 2.9 and 2.5 V, respectively, and their distances to hull are less than 5 meV/atom. By performing nudged-elastic band calculations, we show that the Li-ion transport in these materials takes place by hopping between the nearest neighboring sites with low activation barriers between 0.3 and 0.5 eV. The richness of materials yet to be synthesized in the Li–Fe–S–O phase field illustrates the great opportunity in these mixed anion systems for energy storage applications and beyond.	Jan 2022
	Ligand field-induced exotic dopant for infrared transparent electrode: W in rutile SnO2 Michitaka Fukumoto , Yasushi Hirose , Benjamin A. D. Williamson , Shoichiro Nakao , Koji Kimura , Koichi Hayashi , Yuki Sugisawa , Daiichiro Sekiba , David O. Scanlon , Tetsuya Hasegawa Advanced Functional Materials 9 DOI: 10.1002/adfm.202110832 Show Abstract ▼ Abstract: Transparent conductive oxides (TCOs) exhibiting high near-infrared (NIR) transmittance are one of the key materials for highly efficient thin-film solar cells with widened spectral sensitivity. To realize excellent NIR transparency in a TCO film, developing a dopant providing high mobility (µ) carriers is quite important. Herein, it is demonstrated that W is a high-μ dopant in rutile SnO2, which is unexpected from the conventional strategy. A combination of electrical transport property measurements and hybrid density functional theory calculations reveals that W behaves as a singly charged donor (W5+) showing minimized ionized impurity scattering. This charge state is realized by the splitting of the W 5d t2g-states originating not only from the octahedral crystal field but also hybridization with the O 2p orbitals, whose contribution has not been considered in transition metal-doped TCOs. Hybridization between metal d orbital and O 2p orbitals would provide a new guide for designing a novel dopant of NIR transparent conductors.	Dec 2021
B18-Core EXAFS	Na2.4Al0.4Mn2.6O7 anionic redox cathode material for sodium ion batteries - a combined experimental and theoretical approach to elucidate its charge storage mechanism Cindy Soares , Begoña Silvan , Yong-Seok Choi , Veronica Celorrio , Giannantonio Cibin , David O. Scanlon , Nuria Tapia-Ruiz Journal Of Materials Chemistry A DOI: 10.1039/D1TA05137G Diamond Proposal Number(s): [21847] Open Access Show Abstract ▼ Abstract: Here we report the synthesis via ceramic methods of the high-performance Mn-rich Na2.4Al0.4Mn2.6O7 oxygen-redox cathode material for Na-ion batteries which we use as a testbed material to study the effects of Al substitution and subsequent Na excess in the high-capacity, anionic redox-based cathode material Na2Mn3O7. The material shows a stable electrochemical performance, with a specific capacity of 200 mAh g-1 in the 1.5 - 4.7 voltage window at C/20 and capacity retention of 90 % after 40 cycles. Using a combination of electrochemical and structural analysis together with hybrid density functional theory calculations we explain the behaviour of this material with changes in Mn/anionic redox reactions and associated O2 release reactions occurring in the material during electrochemical cycling (Na insertion/extraction) and compare these findings to Na2Mn3O7. We expect that these results will advance understanding of the effect of dopants in Mn-rich cathode materials with oxygen redox activity to pave their way towards real applications in high-performing sodium-ion battery applications.	Dec 2021
	Enhanced visible light absorption in layered Cs3Bi2Br9 through mixed-valence Sn(II)/Sn(IV) doping Chantalle J. Krajewska , Seán R. Kavanagh , Lina Zhang , Dominik J. Kubicki , Krishanu Dey , Krzysztof Galkowski , Clare P. Grey , Samuel D. Stranks , Aron Walsh , David O. Scanlon , Robert G. Palgrave Chemical Science 12, 14686 - 14699 DOI: 10.1039/D1SC03775G Open Access Show Abstract ▼ Abstract: Lead-free halides with perovskite-related structures, such as the vacancy-ordered perovskite Cs3Bi2Br9, are of interest for photovoltaic and optoelectronic applications. We find that addition of SnBr2 to the solution-phase synthesis of Cs3Bi2Br9 leads to substitution of up to 7% of the Bi(III) ions by equal quantities of Sn(II) and Sn(IV). The nature of the substitutional defects was studied by X-ray diffraction, 133Cs and 119Sn solid state NMR, X-ray photoelectron spectroscopy and density functional theory calculations. The resulting mixed-valence compounds show intense visible and near infrared absorption due to intervalence charge transfer, as well as electronic transitions to and from localised Sn-based states within the band gap. Sn(II) and Sn(IV) defects preferentially occupy neighbouring B-cation sites, forming a double-substitution complex. Unusually for a Sn(II) compound, the material shows minimal changes in optical and structural properties after 12 months storage in air. Our calculations suggest the stabilisation of Sn(II) within the double substitution complex contributes to this unusual stability. These results expand upon research on inorganic mixed-valent halides to a new, layered structure, and offer insights into the tuning, doping mechanisms, and structure–property relationships of lead-free vacancy-ordered perovskite structures.	Nov 2021
	Hidden spontaneous polarisation in the chalcohalide photovoltaic absorber Sn2SbS2I3 Seán R. Kavanagh , Christopher N. Savory , David O. Scanlon , Aron Walsh Materials Horizons 8, 2709 - 2716 DOI: 10.1039/D1MH00764E Open Access Show Abstract ▼ Abstract: Perovskite-inspired materials aim to replicate the optoelectronic performance of lead-halide perovskites, while eliminating issues with stability and toxicity. Chalcohalides of group IV/V elements have attracted attention due to enhanced stability provided by stronger metal-chalcogen bonds, alongside compositional flexibility and ns2 lone pair cations – a performance-defining feature of halide perovskites. Following the experimental report of solution-grown tin-antimony sulfoiodide (Sn2SbS2I3) solar cells, with power conversion efficiencies above 4%, we assess the structural and electronic properties of this emerging photovoltaic material. We find that the reported centrosymmetric Cmcm crystal structure represents an average over multiple polar Cmc21 configurations. The instability is confirmed through a combination of lattice dynamics and molecular dynamics simulations. We predict a large spontaneous polarisation of 37 μC cm−2 that could be active for electron–hole separation in operating solar cells. We further assess the radiative efficiency limit of this material, calculating ηmax > 30% for film thicknesses t > 0.5 μm.	Oct 2021
	Ca4Sb2O and Ca4Bi2O: two promising mixed-anion thermoelectrics Warda Rahim , Jonathan M. Skelton , David O. Scanlon Journal Of Materials Chemistry A 9, 20417 - 20435 DOI: 10.1039/D1TA03649A Open Access Show Abstract ▼ Abstract: The environmental burden of fossil fuels and the rising impact of global warming have created an urgent need for sustainable clean energy sources. This has led to widespread interest in thermoelectric (TE) materials to recover part of the ∼60% of global energy currently wasted as heat as usable electricity. Oxides are particularly attractive as they are thermally stable, chemically inert, and formed of earth-abundant elements, but despite intensive efforts there have been no reports of oxide TEs matching the performance of flagship chalcogenide materials such as PbTe, Bi2Te3 and SnSe. A number of ternary X4Y2Z mixed-anion systems, including oxides, have predicted band gaps in the useful range for several renewable-energy applications, including as TEs, and some also show the complex crystal structures indicative of low lattice thermal conductivity. In this study, we use ab initio calculations to investigate the TE performance of two structurally-similar mixed-anion oxypnictides, Ca4Sb2O and Ca4Bi2O. Electronic-structure and band-alignment calculations using hybrid density-functional theory (DFT), including spin–orbit coupling, suggest that both materials are likely to be p-type dopable with large charge-carrier mobilities. Lattice-dynamics calculations using third-order perturbation theory predict ultra-low lattice thermal conductivities of ∼0.8 and ∼0.5 W m−1 K−1 above 750 K. Nanostructuring to a crystal grain size of 20 nm is predicted to further reduce the room temperature thermal conductivity by around 40%. Finally, we use the electronic- and thermal-transport calculations to estimate the thermoelectric figure of merit ZT, and show that with p-type doping both oxides could potentially serve as promising earth-abundant oxide TEs for high-temperature applications.	Sep 2021
	BaBi2O6: A promising n-type thermoelectric oxide with the pbsb2o6crystal structure Kieran B. Spooner , Alex M. Ganose , W. W. Winnie Leung , John Buckeridge , Benjamin A. D. Williamson , Robert G. Palgrave , David O. Scanlon Chemistry Of Materials 12 DOI: 10.1021/acs.chemmater.1c02164 Show Abstract ▼ Abstract: Thermoelectric materials offer the possibility of enhanced energy efficiency due to waste heat scavenging. Based on their high-temperature stability and ease of synthesis, efficient oxide-based thermoelectrics remain a tantalizing research goal; however, their current performance is significantly lower than the industry standards such as Bi2Te3 and PbTe. Among the oxide thermoelectrics studied thus far, the development of n-type thermoelectric oxides has fallen behind that of p-type oxides, primarily due to limitations on the overall dimensionless figure of merit, or ZT, by large lattice thermal conductivities. In this article, we propose a simple strategy based on chemical intuition to discover enhanced n-type oxide thermoelectrics. Using state-of-the-art calculations, we demonstrate that the PbSb2O6-structured BaBi2O6 represents a novel structural motif for thermoelectric materials, with a predicted ZT of 0.17–0.19. We then suggest two methods to enhance the ZT up to 0.22, on par with the current best earth-abundant n-type thermoelectric at around 600 K, SrTiO3, which has been much more heavily researched. Our analysis of the factors that govern the electronic and phononic scattering in this system provides a blueprint for optimizing ZT beyond the perfect crystal approximation.	Sep 2021

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