When the insulators lanthanum aluminate and strontium titanate are brought together, the interface between them forms a two-dimensional superconductor. Moreover, magnetic imaging of this interface ...shows that superconductivity and ferromagnetism coexist in separated nanoscale domains.
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IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Topotactic phase transformation enables structural transition without losing the crystalline symmetry of the parental phase and provides an effective platform for elucidating the redox reaction and ...oxygen diffusion within transition metal oxides. In addition, it enables tuning of the emergent physical properties of complex oxides, through strong interaction between the lattice and electronic degrees of freedom. In this communication, the electronic structure evolution of SrFeOx epitaxial thin films is identified in real‐time, during the progress of reversible topotactic phase transformation. Using real‐time optical spectroscopy, the phase transition between the two structurally distinct phases (i.e., brownmillerite and perovskite) is quantitatively monitored, and a pressure–temperature phase diagram of the topotactic transformation is constructed for the first time. The transformation at relatively low temperatures is attributed to a markedly small difference in Gibbs free energy compared to the known similar class of materials to date. This study highlights the phase stability and reversibility of SrFeOx thin films, which is highly relevant for energy and environmental applications exploiting the redox reactions.
Topotactic phase transformation coupled with the metal–insulator transition in SrFeOx epitaxial thin films is studied using real‐time optical spectroscopy. The oxygen‐content‐dependent phase transition leads to a pressure–temperature phase diagram of the topotactic transformation. The transformation at relatively low temperatures is ascribed to a markedly small Gibbs' free energy difference between the two structurally distinctive phases.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Thin cylindrical honeycomb-structured aluminum alloy and mono-cast (MC) nylon were studied as superior energy-absorbing materials compared to metallic foams. Their energy-absorbing performance was ...assessed using a modified split Hopkinson pressure bar (SHPB). Key parameters included maximum impact acceleration (a
) and its reduction ratio (compared to the none-specimen case). The lowest a
reduction ratio was observed in bulk Al sheets without honeycomb cavities. As the cavity fraction increased up to 79% in honeycomb-structured Al specimens, the a
reduction ratio improved due to broadened stress-time curves with a shallow-plateau shape. This made high-cavity-fraction Al specimens preferable for higher-energy absorption and lighter-weight buffering materials. In nylon specimens, the a
reduction ratio increased until the fraction reached 52% due the softer and more deformable nature of the polymeric nylon. Thicker or rotated Al specimens also showed higher a
reduction ratios due to sufficient and continuous energy absorption. The modified SHPB demonstrated effective energy-buffering concepts and provided insightful a
interpretations, overcoming complexities in energy absorption analyses.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
4.
Superconductivity in (Ba,K)SbO3 Kim, Minu; McNally, Graham M.; Kim, Hun-Ho ...
Nature materials,
06/2022, Volume:
21, Issue:
6
Journal Article
Peer reviewed
Open access
Abstract
(Ba,K)BiO
3
constitute an interesting class of superconductors, where the remarkably high superconducting transition temperature
T
c
of 30 K arises in proximity to charge density wave order. ...However, the precise mechanism behind these phases remains unclear. Here, enabled by high-pressure synthesis, we report superconductivity in (Ba,K)SbO
3
with a positive oxygen–metal charge transfer energy in contrast to (Ba,K)BiO
3
. The parent compound BaSbO
3−
δ
shows a larger charge density wave gap compared to BaBiO
3
. As the charge density wave order is suppressed via potassium substitution up to 65%, superconductivity emerges, rising up to
T
c
= 15 K. This value is lower than the maximum
T
c
of (Ba,K)BiO
3
, but higher by more than a factor of two at comparable potassium concentrations. The discovery of an enhanced charge density wave gap and superconductivity in (Ba,K)SbO
3
indicates that strong oxygen–metal covalency may be more essential than the sign of the charge transfer energy in the main-group perovskite superconductors.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Oxygen vacancies, especially their distribution, are directly coupled to the electromagnetic properties of oxides and related emergent functionalities that have implications for device applications. ...Here using a homoepitaxial strontium titanate thin film, we demonstrate a controlled manipulation of the oxygen vacancy distribution using the mechanical force from a scanning probe microscope tip. By combining Kelvin probe force microscopy imaging and phase-field simulations, we show that oxygen vacancies can move under a stress-gradient-induced depolarisation field. When tailored, this nanoscale flexoelectric effect enables a controlled spatial modulation. In motion, the scanning probe tip thereby deterministically reconfigures the spatial distribution of vacancies. The ability to locally manipulate oxygen vacancies on-demand provides a tool for the exploration of mesoscale quantum phenomena and engineering multifunctional oxide devices.The properties of complex oxides such as strontium titanate are strongly affected by the presence and distribution of oxygen vacancies. Here, the authors demonstrate that a scanning probe microscope tip can be used to manipulate vacancies by the flexoelectric effect.
Barium bismuth oxide (BaBiO_{3}) is the end member of two families of high-T_{c} superconductors, i.e., BaPb_{1-x}Bi_{x}O_{3} and Ba_{1-x}K_{x}BiO_{3}. The undoped parent compound is an insulator, ...exhibiting a charge density wave that is strongly linked to a static breathing distortion in the oxygen sublattice of the perovskite structure. We report a comprehensive spectroscopic and x-ray diffraction study of BaBiO_{3} thin films, showing that the minimum film thickness required to stabilize the breathing distortion and charge density wave is ≈11 unit cells, and that both phenomena are suppressed in thinner films. Our results constitute the first experimental observation of charge density wave suppression in bismuthate compounds without intentionally introducing dopants.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
We report on a temperature-dependent band gap property of epitaxial MoSe
2
ultrathin films. We prepare uniform MoSe
2
films epitaxially grown on graphenized SiC substrates with controlled thicknesses ...by molecular beam epitaxy. Spectroscopic ellipsometry measurements upon heating sample in ultra-high vacuum showed temperature-dependent optical spectra between room temperature to 850 °C. We observed a gradual energy shift of optical band gap depending on the measurement temperature for different film thicknesses. Fitting with the vibronic model of Huang and Rhys indicates that the constant thermal expansion accounts for the steady decrease of band gap. We also directly probe both optical and stoichiometric changes across the decomposition temperature, which should be useful for developing high-temperature electronic devices and fabrication process with the similar metal chalcogenide films.
We examined the magneto-transport behavior of electrons confined at the conducting LaAlO3/SrTiO3 interface in the low sheet carrier density regime. We observed well-resolved Shubnikov-de Haas quantum ...oscillations in the longitudinal resistance, and plateau-like structures in the Hall conductivity. The Landau indices of the plateaus in the Hall conductivity data show spacing close to 4, in units of the quantum of conductance. These experimental features can be explained by a magnetic breakdown transition, which quantitatively explains the area, structure, and degeneracy of the measured Fermi surface.
•We observed novel plateaus in the Hall conductivity at the LaAlO3/SrTiO3 interface.•The Landau indices of the Hall plateaus have an interval close to 4.•The frequency of quantum oscillations has a sharp transition with magnetic field.•These features can be understood by considering magnetic breakdown orbits.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
This study aimed to develop a structural analysis method to replace and validate large-scale gas gun tests for evaluating the impact resistance of electronic equipment. By measuring projectile's ...deceleration through experiments and simulations, stress and strain during collisions were quantified. It was demonstrated that optimizing projectile and electronic equipment designs could enhance impact resistance. Simulation results indicated that changes in projectile velocity and head angle led to variations in maximum deceleration and penetration depth, with decreasing the head angle proving more effective in reducing maximum deceleration. Comparisons between experimental and simulation results showed good agreement, particularly in plots between maximum deceleration and target collision depth. As the head angle increased, there was a tendency for maximum deceleration to increase and target penetration depth to decrease. Comparing peak deceleration curves from gas gun tests and simulations revealed similar trends, indicating consistent results. This research provides important information for evaluating the impact resistance of electronic equipment and demonstrates that combining experiments with simulations can yield more reliable results.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Cathode active materials and conductive additives for thermal batteries operating at high temperatures have attracted research interest, with a particular focus on compounds offering high thermal ...stability. Recently, FeF3 has been proposed as a candidate for high-voltage cathode materials; however, its commercialization is hindered by its low conductivity. In this study, conductive additives, such as Ni-coated carbon composites (multi-walled carbon nanotubes (MWCNTs) and carbon black (CB)), were utilized to enhance the thermal stability and conductivity of FeF3. The incorporation of metal–carbon conductive additives in the FeF3 composite increased the thermal stability by more than 10 wt.% and ensured high capacity upon conductivity enhancement. The FeF3@Ni/MWCB 15 wt.% composite containing 30 wt.% Ni exhibited a discharge capacity of ∼86% of the theoretical capacity of 712 mAh/g. The use of Ni-coated carbon-based conductive additives will allow the application of FeF3 as an effective high-temperature cathode material for thermal batteries.
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