YBa2Cu3O7-δ Films Research Articles

Study on rapid growth and improved performance of superconducting YBa2Cu3O7-δ coated conductors assisted by transient liquid phase

This study employs a fluorine-free metal organic deposition method (FF-MOD), with transient liquid phase assistance, to expedite the growth (TLAG) of superconducting YBa2Cu3O7-δ (YBCO) thin films on LaMnO3 metal substrates. The research evaluates the phase formation and performance of YBCO films with varying proportions of preformed BaZrO3 (BZO) nanocrystals. The experimental results indicate that the optimal proportion for incorporating BZO nanocrystals is 5 %, leading to the YBCO film displaying critical current density at 77 K under zero-field conditions. This achievement marks a significant advancement in the rapid growth of YBCO films on metal substrates with enhanced current-carrying capacity. Additionally, the research assesses the changes in overall uniformity and microstrain of YBCO films after the addition of BZO nanocrystals, shedding light on the key factors contributing to performance enhancement and offering insights for future improvements. This investigation offers valuable insights for attaining high-speed, high-performance growth of superconducting YBCO coating conductors.

Триплетные сверхпроводящие корреляции гибридной меза-структуры с двухслойной ферромагнитной прослойкой

We present results on electron transport in hybrid Josephson mesa-structure Sd/F1F2/S, consisting of epitaxial films of cuprate superconductor YBa2Cu3O7-δ (Sd), bi-layer ferromagnetic interlayer (F1F2), thin film of metallic Nb was deposited on the top of a thin protective Au film layer used as the upper superconducting electrode (S). The long-range triplet component of superconducting correlations arises when strontium ruthenate SrRuO3 F1 and manganiteLa0.7Sr0.3MnO3 with non-collinear magnetizations are used as ferromagnetic material F2. Superconducting current took place up to the thickness d = 52 nm of the F1F2 interlayer. Superconducting current disappeared in the case of a single ferromagnetic interlayer of manganite (La0.7Sr0.3MnO3 or La0.7Ca0.3MnO3) and SrRuO3 with minimized thicknesses, limited by the occurrence of pinholes. The magnetic field properties of mesa-structure are discussed as well, along with the impact of the second harmonic in the superconducting current-phase relation.

Temporal Evolution of Defects and Related Electric Properties in He-Irradiated YBa2Cu3O7-δ Thin Films.

Thin films of the superconductor YBa2Cu3O7-δ (YBCO) were modified by low-energy light-ion irradiation employing collimated or focused He+ beams, and the long-term stability of irradiation-induced defects was investigated. For films irradiated with collimated beams, the resistance was measured in situ during and after irradiation and analyzed using a phenomenological model. The formation and stability of irradiation-induced defects are highly influenced by temperature. Thermal annealing experiments conducted in an Ar atmosphere at various temperatures demonstrated a decrease in resistivity and allowed us to determine diffusion coefficients and the activation energy ΔE=(0.31±0.03) eV for diffusive oxygen rearrangement within the YBCO unit cell basal plane. Additionally, thin YBCO films, nanostructured by focused He+-beam irradiation into vortex pinning arrays, displayed significant commensurability effects in magnetic fields. Despite the strong modulation of defect densities in these pinning arrays, oxygen diffusion during room-temperature annealing over almost six years did not compromise the signatures of vortex matching, which remained precisely at their magnetic fields predicted by the pattern geometry. Moreover, the critical current increased substantially within the entire magnetic field range after long-term storage in dry air. These findings underscore the potential of ion irradiation in tailoring the superconducting properties of thin YBCO films.

Tuning the superconducting performance of YBa2Cu3O7-δ films through field-induced oxygen doping.

The exploration of metal-insulator transitions to produce field-induced reversible resistive switching effects has been a longstanding pursuit in materials science. Although the resistive switching effect in strongly correlated oxides is often associated with the creation or annihilation of oxygen vacancies, the underlying mechanisms behind this phenomenon are complex and, in many cases, still not clear. This study focuses on the analysis of the superconducting performance of cuprate YBa2Cu3O7-δ (YBCO) devices switched to different resistive states through gate voltage pulses. The goal is to evaluate the effect of field-induced oxygen diffusion on the magnetic field and angular dependence of the critical current density and identify the role of induced defects in the switching performance. Transition electron microscopy measurements indicate that field-induced transition to high resistance states occurs through the generation of YBa2Cu4O7 (Y124) intergrowths with a large amount of oxygen vacancies, in agreement with the obtained critical current density dependences. These results have significant implications for better understanding the mechanisms of field-induced oxygen doping in cuprate superconductors and their role on the superconducting performance.

Ultra-High-Sensitivity and -Stability Thin-Film Heat Flux Sensor Based on Transverse Thermoelectric Effect

In this study, we investigate the sensitivity properties of YBa2Cu3O7-δ thin films with a 15° tilting angle in relation to heat flux density. The films were prepared using the laser pulsed deposition (PLD) technique, and their characteristics were evaluated using various techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), and infrared steady-state and laser transient calibration systems. The YBa2Cu3O7-δ films prepared in this study were found to be of good quality, exhibiting a single-phase structure with strict (001) orientation. Both the substrate and film diffraction peaks were sharp and consistent with the step-flow growth mode, indicating high crystalline quality. Ultra-high sensitivity in the range of 0 to 100 kW/m2, the maximum sensitivity is 230 μV/(kW/m2), and an uncertainty is only 3%. According to the infrared steady-state heat flux calibration system test, when the single output power of the quartz lamp array is 0.2 kW, 0.3 kW, 0.4 kW and 0.5 kW, the maximum output voltage is 0.19 mV, 0.41 mV, 0.63 mV and 0.94 mV, respectively, indicating that the output voltage of the sensor increases with the increase in heat flux, showing a good linear characteristic, and the fitting linearity is 0.99. Through the test of the laser transient thermal current calibration system, the sensors are found to have excellent response–recovery characteristics at 500 kHz and 1000 kHz fiber laser frequencies, and the maximum voltage output is 8.83 mV and 9.09 mV, respectively. Moreover, the component has excellent repeatability, and the maximum measurement error is only 1.94%. Our findings demonstrate the potential of YBa2Cu3O7-δ thin films for use in heat flux sensing applications.

Nanodiamond Influence on the Nucleation and Growth of YBCO Superconducting Film Deposited by Metal-Organic Decomposition.

It was recently shown that the introduction of nanodiamond (ND) into a superconducting metal-organic deposited YBa2Cu3O7-δ (YBCO) film produces an increase in critical current density in self-field conditions (B = 0 T). Such improvement appears to be due to the formation of denser and smoother films than the samples deposited without ND. This paper presents the work done to understand the role of ND during YBCO nucleation and growth. A detailed study on YBCO+ND films quenched at different temperatures of the crystallization process was carried out. Results showed that the reaction responsible for YBCO production appeared effectively affected by ND. In particular, ND stabilizes one of the YBCO precursors, BaF2(1-x)Ox, whose conversion into YBCO requires a prolonged time. Therefore, the YBCO nucleation is slowed down by ND and begins when the experimental conditions favor both thermodynamically and kinetically the formation of YBCO along the c-axis. This effect has important implications because the growth of a highly epitaxial c-axis YBCO film enables excellent superconducting performance.

Interrelations among zero-field critical current density, irreversibility field and pseudogap in hole doped high-Tc cuprates

Critical current density and the irreversibility magnetic fields are two parameters which control most of the applications of high-temperature superconductors. In this brief communications we have investigated the intrinsic effects that determine the magnitudes of these two parameters. The roles of hole concentration in the CuO2 plane (p) and oxygen deficiency (δ) in the CuO1-δ chains on the zero-field low-temperature critical current density, Jc0, were studied for a series of Y1-xCaxBa2Cu3O7-δ (x = 0.00, 0.05, 0.10, and 0.20) thin films. Jc0 above the optimum hole concentration were found to be high. The magnitude of Jc0 were largely determined by the hole concentration, maximizing at p ∼ 0.185 ± 0.005, regardless of the values of x and δ. This implied that oxygen deficiency/disorder plays a secondary role and the intrinsic Jc0 is governed largely by the number of doped holes in the CuO2 planes of Y1-xCaxBa2Cu3O7-δ. Further support in favor of this finding was garnered from the analysis of the in-plane resistive transitions of thin films of YBa2Cu3O7-δ (YBCO) with magnetic fields (H) applied along the crystallographic c-direction. The characteristic magnetic field (H0), linked to the vortex activation energy and the irreversibility field, exhibits similar p-dependence as shown by Jc0(p). We have explained these observations in terms of the doping dependent pseudogap (PG) energy/temperature scale in the low-energy electronic energy density of states observed in high-Tc cuprates. Both the intrinsic critical current density and the irreversibility field depend directly on the superconducting condensation energy, which in turn is primarily determined by the magnitude of the hole concentration dependent PG in the quasiparticle spectral density.

The atomic layer thermopile heat flux sensor based on the inclined epitaxial YBa2Cu3O7-δ films

The atomic layer thermopile (ALTP) heat flux sensor based on highly c-axis oriented YBa2Cu3O7-δ (YBCO) films prepared on miscut 12° LaAlO3 substrates using magnetron sputtering is achieved. Benefiting from good biaxial texture, the YBCO film maintains a large Seebeck coefficient anisotropy, so the sensitivity of the ALTP heat flux sensor reaches 17.54 μV/(kW/m2). In addition, the response frequency of the sensor is higher than 1 MHz due to the high electrical conductivity of the prepared YBCO films, which is also higher than the current maximum (650 kHz) reported in the literature. These results indicate that our ALTP heat flux sensor can realize high-frequency heat flux detection above 1 MHz.

Reduced granularity in BHO-doped YBCO films on RABiTS templates

REBCO based coated conductors (CCs) are a viable alternative to conventional superconductors for many applications, therefore the optimization of their current carrying capacity is an ongoing process. A promising route for the increase in performance is the introduction of artificial pinning centers such as BaHfO3 (BHO) nanoparticles. However, granularity still imposes a substantial performance limitation, especially in REBCO CCs deposited on RABiTS based templates, as the critical current density is severely reduced by moderate misalignment angles of adjacent grains. A combined study of scanning Hall probe microscopy and electron microscopy of undoped and BHO-doped YBa2Cu3O7-δ (YBCO) films on technical templates shows that BHO-doping leads to a denser microstructure of the superconducting layer and higher global and local critical current densities. The statistical evaluation of local current maps allows for a quantification of the magnetic granularity where a reduction of granularity with increasing film thickness, doping and increasing temperature is found. In particular, the dependence of granularity on the film thickness and enhanced film growth through BHO-doping shows the potential for further optimization of YBCO films on RABiTS based templates.

Realizing the Rapid Crystallization of YBa2Cu3O7-δ Films on LaMnO3 Buffer Layer by Induction Heating

Realizing the Rapid Crystallization of YBa2Cu3O7-δ Films on LaMnO3 Buffer Layer by Induction Heating

Rapid phase formation and interfacial reaction of YBa2Cu3O7−δ coated conducts by using high-rate crystallization of fluorine-free chemical solution

In the present work, the high-rate epitaxial growth for superconducting YBa2Cu3O7-δ (YBCO) films on the substrates of LaMnO3(LMO)/IBAD-MgO/Y2O3/Al2O3/Hastelloy is achieved by fluorine-free metal organic deposition (FF-MOD) by rapidly switching the partial oxygen pressure (pO2) at a fixed temperature. Further investigation into the effects of temperature and switching pO2 on the phase transition of YBCO elucidates that the growth mode and microstructural characteristics of the studied films. BaMnO3 heterogeneous particles are observed in localized regions in the films by cross-sectional transmission electron microscopy, which may be generated by the interfacial reactions between the substrate and transient liquid phases. The present work implies the feasibility of FF-MOD for the rapid growth of YBCO films on LMO buffered metallic substrates, regardless of interfacial reactions during the preparation.

Signatures of a strange metal in a bosonic system.

Fermi liquid theory forms the basis for our understanding of the majority of metals: their resistivity arises from the scattering of well defined quasiparticles at a rate where, in the low-temperature limit, the inverse of the characteristic time scale is proportional to the square of the temperature. However, various quantum materials1-15-notably high-temperature superconductors1-10-exhibit strange-metallic behaviour with a linear scattering rate in temperature, deviating from this central paradigm. Here we show the unexpected signatures of strange metallicity in a bosonic system for which the quasiparticle concept does not apply. Our nanopatterned YBa2Cu3O7-δ (YBCO) film arrays reveal linear-in-temperature and linear-in-magnetic field resistance over extended temperature and magnetic field ranges. Notably, below the onset temperature at which Cooper pairs form, the low-field magnetoresistance oscillates with a period dictated by the superconducting flux quantum, h/2e (e, electron charge; h, Planck's constant). Simultaneously, the Hall coefficient drops and vanishes within the measurement resolution with decreasing temperature, indicating that Cooper pairs instead of single electrons dominate the transport process. Moreover, the characteristic time scale τ in this bosonic system follows a scale-invariant relation without an intrinsic energy scale: ħ/τ ≈ a(kBT + γμBB), where ħ is the reduced Planck's constant, a is of order unity7,8,11,12, kB is Boltzmann's constant, T is temperature, μB is the Bohr magneton and γ ≈ 2. By extending the reach of strange-metal phenomenology to a bosonic system, our results suggest that there is a fundamental principle governing their transport that transcends particle statistics.

Secondary epitaxial orientations in high lattice mismatch systems: A case study for YBa2Cu3O7-δ and SrO thin films deposited on (0 0 1)MgO

High lattice mismatch epitaxy is receiving wide attention with demands increasing for bonding together materials of differing types to manage defect content. One interesting aspect of heteroepitaxial growth is in the formation of secondary epitaxial orientations in, often, high lattice mismatch systems. Two examples explored here are the cases of epitaxial thin films of YBa2Cu3O7-δ (YBCO) grown onto (0 0 1)MgO (8.55% lattice mismatch) and SrO on (0 0 1)MgO (12.2% lattice mismatch). Under certain conditions, these materials have been found, using electron microscopy, to contain large twist boundary rotated grains which adopt well defined orientations. In the case of YBCO (SrO) on MgO the most frequent in-plane orientations observed occur at 23.5° (27.4°) on MgO, respectively. These values show that there is an increase in the twist angle of the most frequently observed grain orientations with lattice mismatch as observed experimentally. These have been explained, in the present work, in terms of a novel means of describing the coincident site lattice theory. Indeed, an equation has been derived using this novel theory which closely matched these experimental observations.

Texture and terahertz analysis of YBa2Cu3O7 grown onto LaAlO3 by the chemical solution deposition technique

ABSTRACT We analyze in-plane and out-of-plane texture and terahertz analysis of a YBa2Cu3O7-δ (YBCO) film deposited by chemical solution deposition technique onto LaAlO3 (100) substrate. X-ray diffraction reveals the presence of (00l) reflections for the YBCO phase. The out-of-plane texture, measured by a rocking curve, shows two sub-layers with Δω = 0.45° and 1.8°. The value of the c-axis fraction of the crystallites is 81%. Also, the in-plane texture was studied by ϕ–scan measurements of (102) reflection, displaying mostly a colony of c-axis oriented grains, and two colonies of a-axis oriented grains onto the YBCO surface. In addition, the temperature dependence of the magnetization measurement revealed a critical temperature of 90 K, typical for YBCO superconductor material. From the temperature-dependent optical conductivity of YBCO, we observe an absorption feature at ≈1.57 THz, which redshifts with increasing temperature.

YBa2Cu3O7–δ films prepared by pulsed laser deposition in O2/Ar mixture atmosphere

The YBa2Cu3O7-δ(YBCO) superconducting films were fabricated epitaxially on STO(00 l) substrates by pulsed laser deposition method (PLD) in different O2/Ar mixture atmospheres. The surface morphology of the YBCO film is strongly dependent on the O2/Ar ratio of the ambient atmosphere. The surface particle density decreases and the particle size increases with the O2/Ar ratio decreasing. The lattice parameters and the superconducting transition temperature (Tc0) are almost independent on the O2/Ar ratio and are about the same as 1.168 nm and 90 K, respectively, which can be ascribed to the annealing process in 1 atm O2 for all the YBCO samples. Based on the above results, in O2/Ar ratio of 25:75 atmosphere, YBCO:LaAlO3 superconducting composite films with good performance were prepared by co-deposition of PLD with magnetron sputtering method. The experimental results provide a way to control the surface morphology of the YBCO films deposited by PLD method and provide valuable reference for the preparation of YBCO composite thin films by co-deposition of PLD with magnetron sputtering method in Ar/O2 mixture atmosphere.

Improved biaxial texture of tri-layer YBCO/CaTiO3/YBCO films using an all chemical solution deposition method

The chemical solution deposition (CSD) is one of the most appealing routes for the growth of high-quality YBa2Cu3O7-δ (YBCO) films due to its advantages of low cost and high efficiency. However, as with other preparation methods such as pulsed laser deposition (PLD), the critical current densities (JC) of YBCO films prepared by the CSD method also dramatically decrease with increasing film thickness, which is known as thickness effect. In this paper, the tri-layer YBCO/CTO/YBCO thick films were deposited on buffered Hastelloy C276 tapes by using a dip coater based on all CSD method. By means of the introduction of the CTO interlayer, the JC reduction with increasing film thickness was inhibited, arising from the improvement of the biaxial texture in the tri-layer thick film. The JC value (77 K, self-field) of the tri-layer film was around 3.3 MA/cm2. The texture improvement was mainly ascribed to the interface levelling through the deposition of the CTO interlayer which is a template with good biaxial texture for the epitaxial growth of YBCO film.

High homogeneity 10 cm long BaTiO3-doped YBa2Cu3O7-δ films by the trifluoroacetate metal-organic deposition process

The trifluoroacetate metal-organic deposition (TFA-MOD) is one of the most appealing routes for the growth of high-quality YBa2Cu3O7-δ (YBCO) coated conductors (CCs) due to its advantages of low cost and high efficiency. However, the puzzle of the inhomogeneities in microstructures and superconducting properties of YBCO CCs prepared based on the TFA-MOD route remain still a challenge. In this paper, 10 cm long YBCO films were prepared under different low-pressure conditions. These YBCO films were deposited on buffered Hastelloy C276 tapes using a dip coater. The effect of different ambient pressures on the microstructure and critical current density of YBCO films was investigated. High critical current density (JC) YBCO coated conductors with good homogeneity were obtained. The JC values (77 K, self-field) at different positions along the length direction of YBCO coated conductor were around 3.5–4 MA/cm2. The results showed that only under a suitable pressure the homogeneities of the microstructure and critical current density along the length direction of coated conductor can be greatly improved. The improvement was mainly ascribed to good texture and the absence of impurity phases BaF2 and Ba4Y2O7 in the films.

Interaction between untreated SrTiO3 substrates and solution-derived YBa2Cu3O7-δ films

In this work it is shown how SrTiO3 substrates interact with YBa2Cu3O7-δ thin films during film processing. The effect of this interdiffusion on morphology and transport properties is analyzed. The films were deposited by low fluorine Metal Organic Decomposition (MOD) on SrTiO3 (0 0 1) single crystals. In general, a sharp c-axis oriented growth and high critical temperature (Tc) were observed in all samples; however, the surface of the otherwise good-quality films is spoiled by the presence of inhomogeneous circular areas of seemingly different appearance and texture. In order to understand the nature of these defects, the substrates and the films were deeply investigated by optical microscopy, scanning and transmission electron microscopy (SEM, TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), contact-stylus surface profilometry (SSP), Atomic Force Microscopy (AFM) and time of flight secondary ion mass spectrometry (ToF-SIMS). The round spots are the manifestation, on the film surface, of ion interdiffusion from the substrate into the YBCO film Spot-free samples can be obtained with different pre-treatments of the SrTiO3 substrates. Although these defects are detrimental for the film local structure, Jc values are not significantly affected, although the defects' influence might become substantial while working on smaller scales.

Interfacial-Redox-Induced Tuning of Superconductivity in YBa2Cu3O7-δ.

Solid-state ionic approaches for modifying ion distributions in getter/oxide heterostructures offer exciting potentials to control material properties. Here, we report a simple, scalable approach allowing for manipulation of the superconducting transition in optimally doped YBa2Cu3O7-δ (YBCO) films via a chemically driven ionic migration mechanism. Using a thin Gd capping layer of up to 20 nm deposited onto 100 nm thick epitaxial YBCO films, oxygen is found to leach from deep within the YBCO. Progressive reduction of the superconducting transition is observed, with complete suppression possible for a sufficiently thick Gd layer. These effects arise from the combined impact of redox-driven electron doping and modification of the YBCO microstructure due to oxygen migration and depletion. This work demonstrates an effective step toward total ionic tuning of superconductivity in oxides, an interface-induced effect that goes well into the quasi-bulk regime, opening-up possibilities for electric field manipulation.

Nanodiamond addition to chemical solution deposited YBa2Cu3O7-δ film: effect on structural and superconducting properties

The superconducting properties of YBa2Cu3O7-δ (YBCO) film can be significantly improved through the introduction of nanosized defects. In this work, the Chemical Solution Deposition (CSD) of YBCO film doped with Nanodiamond (ND) is proposed. ND introduction in YBCO (YBCO-ND) has never been reported until our recent preliminary study [1] that showed ND potential for the improvement of YBCO transport properties. Further optimizations of the YBCO-ND CSD process have been accomplished and results are illustrated in the present paper. Good epitaxial films have been obtained and a significant improvement of film morphology and superconducting properties has been observed with respect to pure YBCO. Dopant seems to have a beneficial effect on YBCO morphology. In fact, YBCO-ND films generally show denser, smoother and more connected surfaces. The good morphology corresponds to increased superconducting properties. Higher zero-field critical current densities have been measured in the temperature range from 10 K to 77 K (i.e. 18 and 13 ± 1.2 MA•cm−2 respectively for YBCO-ND and pure YBCO at 10 K). These results could be mainly ascribed to an improvement of the percolation path due to the increase of film density and grain coalescence. It might be supposed that ND influences the nucleation mechanisms of YBCO films facilitating c-axis orientation, but the actual role sill needs to be clarified.