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Substrate engineering is very significant in the synthesis of the high-temperature superconductor (HTS) coated conductor. Here we design and synthesize several distinct and stable Cerium oxide (CeO 2 ) surface reconstructions which are used to grow epitaxial films of the HTS YBa 2 Cu 3 O 7-δ (YBCO). To identify the influence of annealing and post-annealing surroundings on the nature of nucleation centers, including Ar/5%H 2 , humid Ar/5%H 2 and O 2 in high temperature annealing process, we study the well-controlled structure, surface morphology, crystal constants and surface redox processes of the ceria buffers by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and field-emission scanning electronic microscopy (FE-SEM), respectively. The ceria film post-annealed under humid Ar/5%H 2 gas shows the best buffer layer properties. Furthermore, the film absorbs more oxygen ions, which appears to contribute to oxygenation of superconductor film. The film is well-suited for ceria model studies as well as a perfect substitute for CeO 2 bulk material. [ABSTRACT FROM AUTHOR]

Oxygenation is one of the most essential processes for practical applications of REBa 2 Cu 3 O 7−δ (RE123, RE = Y, Gd etc. rare earths) superconductors. Second generation high-T c superconducting coated conductors are based on biaxial textured RE123 thin films, on which, a cover layer of silver for protecting is normally applied. It results in a little more complicated oxygenation process compared to naked film without silver protective layer. In the present work, a series of absorbing oxygen post-annealing processes were carried out for YBa 2 Cu 3 O 7−δ coated conductors. The oxygen diffusion procedure and the kinetics in the annealing process were investigated. Analysis and calculations show that the activation energy was 1.01 eV, consistent with previous reports. Moreover, experiments show that the “over-doping” phenomena frequently occurs in coated conductors, and thus dropping the T c to as low as 86–88 K. To improve the temperature margin for practical applications (temperature difference between the superconducting transition temperature T c and application temperature), we investigated the potential of increase in T c by preventing from the “over-doped” happening, while keeping oxygen in order. Finally, by employing the new annealing process, we can produce long (several hundred meters) coated conductor with high T c,onset (92 K), narrow transition width and stable performance. [ABSTRACT FROM AUTHOR]

The influence of various gas flow conditions on the nucleation and growth rate of YBa 2 Cu 3 O 7-δ (YBCO) coated conductors in the high-temperature heat treatment stage of low fluorine chemical solution deposition (LF–MOD) process have been investigated, including the gas flow rate and gas flow direction. The results indicated that film-growth rate is faster while a -axis oriented phase coexisted with c -axis in the films at the higher gas flow rate. And YBCO ( 00 l) grains grew slowly while a -axis oriented phase also nucleated easily on the end of the long films along gas flow direction. It could be caused by large quantities of HF gas accumulating from the chemical reaction for converting YBCO phase. Hence, the crystal mechanism of various LF–MOD methods can be supposed as still “BaF 2 ” process as the TFA-MOD method, and orientation nucleation and growth rate of YBCO films can be artificial control by adjusting the gas flow conditions. [ABSTRACT FROM AUTHOR]

Thick YBaCuO (YBCO) films grown by metallorganic deposition (MOD) are very significant for high-performance superconducting wires. In the present work, the modified MOD method with reduced fluorine content in precursor solution (namely LF-MOD in the following) is applied to prepare the YBCO films with the purpose of reducing the processing time as well as increasing thickness. Five-layer YBCO films with a thickness of more than 2.5 μm are achieved after the effect of high-temperature annealing time ( t) on the morphology and texture of YBCO films is systematically investigated. It is suggested that an annealing time as long as 6 h appears necessary to achieve a good performance for such a thick YBCO film. To understand the evolution of texture with thickness, plasma etching is employed to characterize the profile morphology at different depths inside the films, revealing the a-axis grains together with the impurity phases arising from the incomplete reaction mostly present at the top surface only. [ABSTRACT FROM AUTHOR]

This work presents a study of the evolution of the phases in the intermediate heat treatment process (IHP) which was after the pyrolysis process and before the crystallization of YBCO superconducting thin films. It was shown that the evolution of the solid solution could always take place whether with or without water vapor and oxygen. When water vapor is present in the atmosphere, the evolution temperature of the intermediate phase was lower than the one without vapor. The intermediate phase of YCuO with the vapor was observed at 680 °C. By calculating the changes of Gibbs free energy of reactions possibly involved in the IHP, the priority reaction with water vapor was CuF>YF>BaF when CuF, YF, and BaF coexisted while CuF and YF prefer to react with BaO to form BaF while they coexisted. The appearance of intermediate phase features could be illustrated through the calculation. [ABSTRACT FROM AUTHOR]

A simple and efficient way to planarize Hastelloy substrate for high-temperature superconductors has been developed. The colloid-solution deposition planarization (CSDP) method consists of two steps: colloid deposition planarization and subsequent precursor solution deposition planarization. The surface roughness of Hastelloy belt decreased from 4.0 to 0.8 nm after YO colloid deposition and then to 0.3 nm after further yttrium acetate solution deposition. The shrinkage percentage of the colloid deposition layer and solution deposition layer was 20 and 77 %, respectively. Compared with traditional solution deposition planarization, the higher planarization efficiency of CSDP can be attributed to the lower shrinkage percentage of the colloid deposition layer. As a result, ion-beam-assisted deposition (IBAD)-MgO on Hastelloy substrate with CSDP coating showed crystal orientation. Hastelloy belt planarized by the CSDP method will provide a low-cost substrate for high-temperature superconductors. [ABSTRACT FROM AUTHOR]

The possible exhaustion of fossil fuels in the near future and soaring global energy demand have driven the search for new types of sustainable and renewable alternatives. Perovskite (CHNHPbX, X = I, Br, Cl) solar cells are a type of solar cell based on a perovskite absorber, most commonly a tin halide-based or hybrid organic-inorganic lead material, as the visible-light sensitizer layer, which produces electricity from sunlight. Recently, perovskite solar cells have received substantial worldwide attention. Compared with traditional solar cells, the perovskite solar cells can obtain high efficiency with a simple architecture and via a cost-effective process. In the latest 5 years, the efficiency of perovskite solar cells to convert power has skyrocketed from 3.8 % to more than 19.3 %. It is the fastest advancing solar technology to date. The highest efficiency demonstrated by perovskite solar cells is higher than that of dye-sensitized solar cells (DSSCs). A lager number of research groups have demonstrated that perovskite solar cells may ultimately boost efficiency as high as 25 %. The high efficiency and cheap production costs make it evident that perovskite solar cells have great potential to be commercialized soon. In this review, the history, materials, processing and architecture of solar cells are discussed to obtain a better understanding of high-performance perovskite solar cells. [ABSTRACT FROM AUTHOR]

Y 1– x Gd x Ba 2 Cu 3 O 7–δ -Ag ( x = 0, 0.25, 0.5, 0.75, 1) thin films were prepared on oxide buffered Hastelloy substrates by low fluorine metalorganic depostion (MOD) process. The effects of co-doping of Ag and Gd on the microstructures and superconducting properties of YBCO thin films are investigated with respect to improvement on texture and superconducting performance in case of optimized doping content. It is found that optimum addition of Ag and Gd may lead to better c -axis orientation, superior surface microstructure and finally give rise to much improvement of superconducting performance. [ABSTRACT FROM AUTHOR]

Comparing with conventional physical vapor deposition methods, electrochemistry deposition technique shows a crack suppression effect by which the thickness of CeO 2 films on Ni–5 at.%W substrate can reach a high value up to 200 nm without any cracks, make it a potential single buffer layer for coated conductor. In the present work, the processes of CeO 2 film deposited by electrochemistry method are detailed investigated. A hydroxide reactive mechanism and an oxide reactive mechanism are distinguished for dimethyl sulfoxide and aqueous solution, respectively. Before heat treatment to achieve the required bi-axial texture performance of buffer layers, the precursor CeO 2 films are identified in nanometer scales. The crack suppression for electrochemistry deposited CeO 2 films is believed to be attributed to the nano-effects of the precursors. [ABSTRACT FROM AUTHOR]

Bilayer buffer architecture of Gd 2 Zr 2 O 7 (GZO)/Y 2 O 3 was prepared on the biaxially textured tape of Ni–5 at% W (NiW) by reactive sputtering deposition technique. The buffer layer of GZO films were deposited with different thicknesses on Y 2 O 3 seeding layer with a given thickness of 20 nm. According to the results of φ-scan, the in-plane FWHMs of GZO films decreased and then reversed with increasing thickness of GZO, which corresponded with the in-plane FWHMs and superconducting properties of YBa 2 Cu 3 O 7− δ (YBCO) films. Reflection High-Energy Electron Diffraction (RHEED) was carried out to examine the surface texture of GZO films and the deteriorated surface alignment was found for thicker films. The thickness effect of GZO on performance of YBCO is the coupling result of surface texture and blocking effect caused by thickness. With the balance of these two factors, the YBCO/GZO(120 nm)/Y 2 O 3 /NiW architecture exhibit relatively high performance with the transition temperature T c of 92 K, a transition width Δ T c below 1 K, and a critical current density J c of 0.65 MA/cm 2 . [ABSTRACT FROM AUTHOR]

Abstract: Composite photoelectrodes consisting of mesoporous TiO2 and three-dimensional (3D) fluorine-doped tin oxide (FTO) conductive grid were fabricated. The nanostructures of prepared photoelectrodes were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The power conversion performances of DSCs based on composite photoelectrodes were investigated by the current density–voltage (J–V) characteristics. Compared to TiO2 based DSCs, DSCs based on FTO conductive grid exhibit higher short-circuit current density (J sc) and power conversion efficiency (PCE). The analysis on electrochemical impedance spectroscopy (EIS) reveals that the higher photoelectric conversion performance of DSCs with FTO conductive grid is attributed to more competitive electron collection than recombination. [Copyright &y& Elsevier]

• The frequency characteristics of the HTS wireless power transmission (WPT) system was investigated systematically. • The peak of the maximum output power of the HTS-Cu WPT system will appear at a low frequency. • The use of HTS coils instead of copper coils could significantly improve the transmission efficiency and load reception power of WPT systems in the low-frequency range. Wireless power transmission (WPT) based on magnetically coupled resonance technology, providing high power energy transmissions at longer distances, is promising for practical applications such as the charging of electric vehicles. The traditional WPT system needs to operate at high frequencies to keep efficient energy transmission, and as a result, it requires a high-frequency AC power supplement where pronounceable energy losses may arise from. In the present paper, a high-temperature superconducting (HTS) WPT system is proposed to enable efficient energy transfer at low operating frequencies. The maximum output power and transmission efficiency of HTS-Cu and Cu-Cu WPT systems were compared experimentally with operating frequencies from 33 kHz to 342 kHz. The results show that the usage of the HTS-Cu WPT system can significantly improve the maximum transmission efficiency as well as the output power, especially at low operating frequencies. This provides a method for high-power WPT applications in the low-frequency range. [ABSTRACT FROM AUTHOR]

In this work, we synthesized the Co 50 V 34 Ga 16 alloy by directional solidification technique. Interestingly, the Griffiths phase was found in Co-V-Ga alloy for the first time. Using the DSC curve and the inverse DC susceptibility (χ −1) in the high temperature region, the spontaneous magnetization revealed the existence of Griffiths phase in the high temperature region. And then, according to Arrott plot, the phase transition was determined around the T C. Modified form of the Bean-Rodbell model, considering a shape memory alloy material with compressibility, spin and spin density, one defines the parameter ε , which is 0.26, (ε < 1), further confirmed the transition type around T C. At low temperature, spin wave excitation (Heisenberg ferromagnetic type) was used to study the dependence of spontaneous magnetization on temperature to investigate half metallicity. • Griffiths phase was first discovered in directional solidification of Co 50 V 34 Ga 16 alloy. • Susceptibility and Spontaneous magnetization confirm the existence of Griffiths phase. • Arrott plots and Bean-Rodbell model to determine the transition type around T C. • Spin wave excitation was used to reveals ferromagnetic properties of the alloy at low temperatures. [ABSTRACT FROM AUTHOR]

Abstract: Hall coefficient and resistivity are studied systematically for Pr1.85Ce0.15CuO4−y (PCCO) and Pr1.85Ce0.15Cu0.96V0.04O4−y with varying oxygen content y. As the annealing temperature increases, T c gradually increases, it proves that high annealing temperature not only reduce the oxygen content by removing the apical oxygen, but also change the electronic structure and, accordingly, improve the coupling of the carriers. Small amount of V4+ substitution for Cu site improve the superconductivity of electron-doped superconductor PCCO system. [Copyright &y& Elsevier]

Flat bands and Dirac cones in materials are the source of the exotic electronic and topological properties. The Lieb lattice is expected to host these electronic structures, arising from quantum destructive interference. Nevertheless, the experimental realization of a 2D Lieb lattice remained challenging to date due to its intrinsic structural instability. After computationally designing a Platinum-Phosphorus (Pt-P) Lieb lattice, it has successfully overcome its structural instability and synthesized on a gold substrate via molecular beam epitaxy. Low-temperature scanning tunneling microscopy and spectroscopy verify the Lieb lattice's morphology and electronic flat bands. Furthermore, topological Dirac edge states stemming from pronounced spin-orbit coupling induced by heavy Pt atoms are predicted. These findings convincingly open perspectives for creating metal-inorganic framework-based atomic lattices, offering prospects for strongly correlated phases interplayed with topology., (© 2024 Wiley‐VCH GmbH.)

The interaction of atomic orbitals at the interface of perovskite oxide heterostructures has been investigated for its profound impact on the band structures and electronic properties, giving rise to unique electronic states and a variety of tunable functionalities. In this study, we conducted an extensive investigation of the optical and electronic properties of epitaxial NdNiO 3 synthesized on a series of single-crystal substrates. Unlike nanofilms synthesized on other substrates, NdNiO 3 on SrTiO 3 (NNO/STO) gives rise to a unique band structure featuring an additional unoccupied band situated above the Fermi level. Our comprehensive investigation, which incorporated a wide array of experimental techniques and density functional theory calculations, revealed that the emergence of the interfacial band structure is primarily driven by orbital hybridization between the Ti 3d orbitals of the STO substrate and the O 2p orbitals of the NNO thin film. Furthermore, exciton peaks have been detected in the optical spectra of the NNO/STO film, attributable to the pronounced electron-electron (e-e) and electron-hole (e-h) interactions propagating from the STO substrate into the NNO film. These findings underscore the substantial influence of interfacial orbital hybridization on the electronic structure of oxide thin films, thereby offering key insights into tuning their interfacial properties.

Owing to its inherent non-trivial geometry, the unique structural motif of the recently discovered kagome topological superconductor AV 3 Sb 5 (A = K, Rb, Cs) is an ideal host of diverse topologically non-trivial phenomena, including giant anomalous Hall conductivity, topological charge order, charge density wave (CDW), and unconventional superconductivity. Despite possessing a normal-state CDW order in the form of topological chiral charge order and diverse superconducting gaps structures, it remains unclear how fundamental atomic-level properties and many-body effects including Fermi surface nesting, electron-phonon coupling, and orbital hybridization contribute to these symmetry-breaking phenomena. Here, the direct participation of the V3d-Sb5p orbital hybridization in mediating the CDW phase transition in CsV 3 Sb 5 is reported. The combination of temperature-dependent X-ray absorption and first-principles studies clearly indicates the inverse Star-of-David structure as the preferred reconstruction in the low-temperature CDW phase. The results highlight the critical role that Sb orbitals play and establish orbital hybridization as the direct mediator of the CDW states and structural transition dynamics in kagome unconventional superconductors. This is a significant step toward the fundamental understanding and control of the emerging correlated phases from the kagome lattice through the orbital interactions and provides promising approaches to novel regimes in unconventional orders and topology., (© 2022 Wiley-VCH GmbH.)

High-quality Co-doped BaFe 2 As 2 thin films with thickness up to 2 μm were realized on flexible metal tapes with LaMnO 3 as buffer layers fabricated by an ion beam-assisted deposition technique. Structural analysis indicates that increasing thickness does not compromise the film crystallinity, except for a small amount of impurities. Two types of thickness dependence of critical current density ( J c ) were found: one is almost thickness independent in the range of 0.6-1.5 μm and the other is highly thickness dependent. In addition, the maximum value for crucial current I c at 9 T and 4.2 K is about 55 A/12 mm-W for the 1.5-μm-thick film. Anisotropic Ginzburg-Landau scaling demonstrates that dominant pinning centers develop from correlated to uncorrelated with increasing film thickness. The further theoretical analysis shows that with film thickness increasing the pinning mechanism evolves progressively from a δl pinning to the δT c pinning mechanism., Competing Interests: The authors declare no competing interests., (© 2021 The Author(s).)

The main objective of this work was to study the superconducting properties of RE BCO films with a mixture of rare-earth ( RE ) ions with large difference in ion size, in particular Sm 3+ and Yb 3+ . These Yb 1- x Sm x Ba 2 Cu 3 O 7- δ films have been successfully prepared for the first time by chemical solution deposition following the extremely low-fluorine route, which allows reducing the fluorine content by 93% with respect to standard full trifluoroacetate solutions. On the one hand, critical temperature T c remains stable at approximately 90 K with Sm content up to x = 0.5 where T c starts to increase towards the values of pure SmBCO films of approximately 95 K. On the other hand, the critical current densities J c of the pure SmBCO films are the largest at 77 K, where the influence of a higher T c is very relevant, while at lower temperatures and low fields, the mixed films reach larger values. This demonstrates that mixing rare-earth elements RE in RE Ba 2 Cu 3 O 7- δ causes a change in the pinning properties of the films and reveals the importance of selecting adequate RE BCO compounds according to the temperature and magnetic field region of a desired application., Competing Interests: We declare we have no competing interests., (© 2020 The Authors.)

The investigations into the interfaces in iron selenide (FeSe) thin films on various substrates have manifested the great potential of showing high-temperature-superconductivity in this unique system. In present work, we obtain FeSe thin films with a series of thicknesses on calcium fluoride (CaF 2 ) (100) substrates and glean the detailed information from the FeSe/CaF 2 interface by using scanning transmission electron microscopy (STEM). Intriguingly, we have found the universal existence of a calcium selenide (CaSe) interlayer with a thickness of approximate 3 nm between FeSe and CaF 2 in all the samples, which is irrelevant to the thickness of FeSe layers. A slight Se deficiency occurs in the FeSe layer due to the formation of CaSe interlayer. This Se deficiency is generally negligible except for the case of the ultrathin FeSe film (8 nm in thickness), in which the stoichiometric deviation from FeSe is big enough to suppress the superconductivity. Meanwhile, in the overly thick FeSe layer (160 nm in thickness), vast precipitates are found and recognized as Fe-rich phases, which brings about degradation in superconductivity. Consequently, the thickness dependence of superconducting transition temperature (T c ) of FeSe thin films is investigated and one of our atmosphere-stable FeSe thin film (127 nm) possesses the highest T c onset /T c zero as 15.1 K/13.4 K on record to date in the class of FeSe thin film with practical thickness. Our results provide a new perspective for exploring the mechanism of superconductivity in FeSe thin film via high-resolution STEM. Moreover, approaches that might improve the quality of FeSe/CaF 2 interfaces are also proposed for further enhancing the superconducting performance in this system.