YBa2Cu3O7 Films Research Articles

94-K Superconducting Yttrium Barium Cuprate Films Prepared by Spray Pyrolysis of Methacrylate Solutions

High-Tc YBa2Cu3O7 films 2–6 μm in thickness were deposited onto lanthanum aluminate substrates by spray pyrolysis of methacrylate solutions, and their properties were studied. By optimizing the deposition conditions (substrate material, solution concentration, and firing schedule), single-phase, nearly stoichiometric films well adherent to the substrate were obtained, with Tc = 94 K and ΔT = 9 K.

Effects of ozone assisted deposition on the dielectric properties of 90° off-axis radio frequency magnetron sputtered SrTiO3

The low and high frequency dielectric properties of epitaxial SrTiO3 (STO) thin films deposited on LaAlO3 are presented. The effects of in situ ozone annealing during the early stages of deposition were explored. X-ray diffraction results indicated that the ozone treatment resulted in more symmetric and sharper diffraction peaks. In addition, the peaks for the ozone treated samples were shifted in 2θ towards values approaching the bulk. The dielectric constant of the ozone treated samples increased from 275 at room temperature to 1175 at 22 K (measured at 100 kHz). The effective loss tangent of the device remained between 1×10−4 and 1×10−3 down to 100 K, where it began to increase. These properties were far superior to those films deposited without ozone. For high frequency measurements, coplanar waveguide structures with a centerline width of 20 and 40 μm wide gaps were patterned into YBa2Cu3O7 films deposited on top of the 0.5 μm thick STO. For the ozone treated films, Q values of up to 70% greater were achieved at 4 GHz and 75 K with little effect on the frequency modulation (compared to films deposited without ozone).

Accurate Measurements of Surface Resistance of HTS Films Using a Novel Transmission Mode Q-Factor Technique

Microwave characterization of HTS films, using typically a sapphire dielectric resonator can only be as accurate as the Q0-factor and fres measurements. A novel Transmission Mode Q-Factor (TMQF) technique has been used for accurate measurements of surface resistance of YBa2Cu3O7 films, with errors lower than 1%. The method allows for accurate determination of QL, β1, and β2 based on novel equations and a multi-frequency circle-fitting technique applied to S21, S11, and S22 measured around the resonance. Parasitic effects introduced by real measurement systems, namely, noise, crosstalk, coupling loss, coupling reactance, and electrical delay due to uncalibrated transmission lines are compensated for in the new method. Range of unloaded Q0-factors that can be measured with the TMQF technique is assessed to be from 100 to 10 million at the GHz range of frequencies.

Dual mode cross-slotted filters realized with superconducting films

A planar superconducting single stage dual mode filter has been investigated and tested. The basic element of the device is a square patch resonator diagonally crossed by unequal slots to provide both a size reduction and a simple way to couple the two degenerate modes. The effect of further cuts, realized on the conductor surface, is also investigated with respect to the power handling capability and miniaturization requirements. Two different filter topologies operating in C band with 1% fractional bandwidth have been designed and fabricated using Nb and YBa2Cu3O7 films grown on 10×10×0.5 mm3 LaAlO3 (100) substrates. Device response is studied performing power and intermodulation measurements. Third order products start to appear above the noise floor (−120 dBm) at input power Pin≈−20 dBm, whereas thermomagnetic breakdown is observed above 20 dBm.

J c enhancement of YBa2Cu3O7 films on polycrystalline silver substrates by metalorganic chemical vapor deposition in high magnetic fields

High-quality YBa2Cu3O7 (YBCO) films were grown on polycrystalline silver substrates by a metalorganic chemical vapor deposition process in high magnetic fields. Property characterizations revealed that the YBCO films deposited in high magnetic fields have excellent structural and superconducting properties. At 77 K, the transport critical current densities of such films were over 10 000 A/cm2 in the field of 1 T (H∥c axis). The improvement of the critical currents in YBCO films deposited in high magnetic fields is correlated with the better intergrain connections, as observed by scanning electron microscopy.

Electrodeposited films of YBa 2Cu 3O 7−x on Ag and on SrTiO 3: a comparison

Thick films (∼ 30μ) of YBa 2Cu 3O 7−x (YBCO) have been obtained through cationic electrodeposition on silver and on reduced SrTiO 3, so as to make it conducting and eliminate the need for a conducting buffer layer (Spanish patent P9802655). The superconducting films morphology is, in both cases, of a columnar type, as shown by SEM, leaving some empty spaces in between the columns. These spaces can be diminished, when silver is used as a substrate, by a multiple sequential electrodeposition. Although the films are then not continuous, critical temperatures are as high as usual (∼ 92 K) and critical currents (as determined by the Bean method) are, in A/cm 2, respectively 9 500 for YBCO/Ag and 3 250 for YBCO/SrTiO 3.

Vortex Pinning Regimes in thin films of YBa 2Cu 3O 7−δ

The field dependence of the superconducting current density j s ( B) and the pinning energy U c( B) in thin films of YBa 2Cu 3O 7−δ indicates three different pinning regimes. At low fields, μ 0 H < B * ≈0.7 n d φ 0 ( n d is the density of dislocations), j s ( B) is constant and U c = 600K at T = 0 for all YBa 2Cu 3O 7−δ films, independent of the density of dislocvations. This is much lower than the pinning energy of a vortex in a single dislocation, for which U c ≈ 6000K. At intermediate fields, B * < μ 0 H < 0.5T, a sharp decreae of U c is observed. For μ 0 H> 0.5T, U c ( B) is constant again, with U c ( B) ≈ 80K for sputtered films and U c ( B) ≈ 200K for laser ablated films.

Thin HTSC films produced by a polymer metal precursor technique

In precursors the metal ions are combined with acid groups of polymethacrylic acid (PMAA), polyacrylic acid (PAA) or novolac. Compared to thermal degradation temperature of pure polymers those of precursors are low. Precursors films were patterned by UV lithography. Diffractometric investigations showed that the c-axis oriented epitaxial films of YBa 2Cu 3O x and Bi 2Sr 2CaCu 2O x originated from amorphous metal oxide films, which were received after thermal degradation of the precursor. Transition temperatures and current densities were determined by electric resistivity measurements.

Mixed-state Hall effect in high-temperature superconductors in small and large magnetic fields

In many high-temperature superconductors, the Hall effect in the mixed superconducting state has a sign opposite to that in the normal state. Some highly anisotropic materials exhibit even a double sign reversal of the mixed-state Hall effect. We investigate this anomaly in precisely-patterned thin films of YBa 2Cu 3O 7−δ (YBCO) in a large range of magnetic fields from 32 mT to 13 T. The Hall conductivity appears to decompose into two contributions of different sign. The positive (hole-like) part increases steeply below the critical temperature and indicates that the scattering rate of the quasiparticles in the superconducting state is drastically reduced. The negative contribution is present around the critical temperature and becomes important in low fields only. The delicate interplay between these two contributions, together with the cutoff of the experimental window by pinning, leads to the various experimental observations, and eventually to a double sign change in fields below 0.25 T that has not been observed previously in YBCO.

Fabrication and characterisation of underdoped YBa 2Cu 3O 7-δ thin films

Thin c-axis films of YBa 2Cu 3O 7-δ have been grown on single crystal (001) MgO by pulsed laser deposition. The films have been deoxygenated by sintering and annealing in a reduced pressure of O 2. The process is reproducible, controllable and reversible. The reduction in T c is accompanied by a systematic elongation in c-axis, facilitating an inference of δ. Resistance measurements show a departure from linearity at the pseudogap formation temperature T ∗, which has been determined as a function of δ.

Dielectric function of YBCO in the mid-infrared: temperature and doping dependence at 3.392μm

The ab-plane dielectric function at 3392nm of thin films of YBa 2Cu 3O 7−δ with a wide range of doping has been measured using attenuated total reflectance. While ε 2, and therefore σ 1, are temperature independent, | ε 1| decreases by ∼25% with increasing temperature. A stronger dependence on doping is observed: the magnitudes of ε 1 and ε 2 are both strongly suppressed as δ increases. A generalised Drude analysis shows that the plasma frequency is temperature-independent, but scales with doping. The scattering rate increases with temperature, and also increases with decreasing doping, consistent with stronger coupling in the underdoped regime.

Upper critical magnetic field of ion-irradiated YBaCuO and NdCeCuO films

It has been found that the high-energy He-ion irradiation effect on the upper critical magnetic field H c2(T) of YBaCuO and NdCeCuO epitaxial films is the same as the result of variations of oxygen content or ration Nd/Ce. In all these cases the effect of the electron scattering change on the resistivity and the H c2 is not significant in comparison with a dramatic change of the electron structure.

Pinning mechanism of vortices at antiphase boundaries in YBaCuO films

Antiphase boundaries represent dislocation free interfaces in YBaCuO with small structural width of less than 1 nm. We show, that strong pinning at such boundaries takes places by quasiparticle scattering induced variation of the condensation energy, characteristic of superconductors with anisotropic gap. The length scale of the order parameter suppression at antiphase boundaries will be discussed.

Monte Carlo modeling of electron beam physical vapor deposition of yttrium

As part of a study on the deposition of superconducting films of YBa2Cu3O7−δ, a three-dimensional electron beam physical vapor deposition process of yttrium in a vacuum chamber is investigated both computationally and experimentally. The numerical analysis employs the direct simulation Monte Carlo (DSMC) method. The experimental studies consist of atomic absorption spectra taken in the evaporated yttrium plume and deposited film thickness profiles. Some important modeling issues such as atomic collision cross sections for metal vapors and hyperfine electronic structure of the atomic absorption spectra are addressed. Film deposition thicknesses on the substrate and atomic absorption spectra given by the DSMC method and experiment are in excellent agreement. Collisions between the atoms are found to have a significant effect on the film growth rate and area of uniform deposition as the evaporation rate of yttrium increases.

Enhanced pinning in a magnetic-superconducting bilayer

Pinning of vortices in a high-temperature superconductor by the magnetic domain structure of a highly anisotropic ferromagnet is investigated by means of magnetic measurements in nanoscale period superconductor/ferromagnet (SC/FM) heterostructures. Two different samples consisting of highly epitaxial films of YBa2Cu3O7(SC) and BaFe12O19(FM) are analyzed relative to a pure superconducting YBa2Cu3O7 film. The irreversibility line obtained in the magnetic-field-reduced-temperature phase diagram for each heterostructure is found to shift upwards when compared to the line corresponding to the pure superconducting sample. This effect is interpreted as an evidence for the enhancement of pinning of vortices in the SC layer by the magnetic domain structure in the FM layer.

The low-temperature electric conductivity of YBaCuO and LaSrMnO dielectric films obtained by a pulsed laser sputter deposition technique

We have studied the electric conductivity of YBaCuO and LaSrMnO dielectric films obtained by pulsed laser sputtering of targets possessing metallic conductivity. The plots of the sample resistance versus temperature R=R(T) measured at T<T cr(T cr=160–240 K) exhibit regions where R is independent of the temperature. This phenomenon is probably related to manifestations of the quantum confinement effects upon the conversion of small grains into quantum dots. In the region of T<T cr, the electric conductivity of the system is determined by a mechanism of the phononless electron tunneling with participation of the atomic-type states belonging to small grains (clusters) featuring metallic conductivity in the amorphous matrix.

Study of the rate-limiting processes in liquid-phase epitaxy of thick YBaCuO films

Liquid-phase epitaxy was used to grow c-axis YBa 2Cu 3O 7−δ thick films on NdGaO 3 (1 1 0) substrates in an Y supersaturated BaO–CuO solvent. In the case of stationary substrates, the familiar √ t growth kinetics is found. Substrate rotation was employed in order to induce forced convection in the liquid, thereby reducing the thickness of the diffusion boundary layer. The resulting growth kinetics showed transient and steady-state growth regimes. The transient regime extends to about 200 s with √ t growth kinetics. In the steady-state regime, diffusion across an established diffusion boundary layer led to a linear increase of film thickness with time. This diffusion boundary layer was estimated to be ∼35 μm for a substrate rotating at 200 rpm. Detailed study of the film growth suggested the presence of an interface kinetics that limited the growth on a competitive basis with volume diffusion in the liquid. The phenomenological kinetic coefficient is found to be ∼2.5×10 −6 m s −1, which is significantly higher than theoretically predicted. The diffusion coefficient of Y in the solution was estimated from viscosity (Stokes–Einstein and Sutherland relations) to be around 2.9–4.3×10 −10 m 2 s −1 at 990°C, while the growth data gave a value of ∼4×10 −10 m 2 s −1.

Interfacial Microstructure and Crystallographic Orientations of Thick YBa2Cu3O7 Films Deposited on CeO2/LaAlO3 Substrate

Abstract The development of YBa2Cu3O7 (YBCO) thick films on a flexible, textured, metallic substrate has recently attracted considerable scientific and technical interest. It is well known that the interfacial microstructure plays an important role on the formation and alignment of the YBCO films. Thus, understanding the evolution of the phases near the substrate interface will help us to improve the quality of the films. In this study, BaF2, Cu, and Y were deposited on the (001) CeO2/LaAlO3 substrates without external heating in vacuum. Subsequently, a series of these films were annealed at 735°C for preselected time periods and then quenched. Similar to YBCO films on SrTiO3 substrates, (Ba, Y, Cu)(F,O)2 (precursor) and Cu2O phases were formed after annealing for 10 minutes. After 12 hours annealing, the formation of YBCO film was completed.

Thermal boundary resistance of YBa2Cu3O7 on MgO films deducedfrom the transient V(I) response

In narrow YBa2Cu3O7 films, we have measured the delay timebetween the excitation by a critical current pulse and the voltage response,and analysed it on the basis of a time-dependent Ginzburg-Landau equation toprovide the gap relaxation time. In the present experimentalsituation, thisparameter can be identified with the phonon escape time, and so it providesinformation on the film-to-substrate thermal resistance. Our results forvarious conditions of thickness and of temperature are consistent with otherindependent data found either in our laboratory or reported in the literature.This new procedure is fast and applicable at any temperature belowTc.

Preparation of YBCO superconducting thick film by electrophoresis

The thick films of YBa 2Cu 3O x (YBCO) superconductor were prepared by electrophoretic deposition, using pre-sintered YBCO powder dispersed in acetone solution. The alumina (Al 2O 3) ceramic plate, coated with Ag, was used as the cathode substrate and the stainless steel mesh electrode was used as the counter electrode in suspension for electrophoresis. The conditions of applied voltages and temperatures, contents of iodine additives, and deposition times for electrophoretic deposition of YBCO thick films were studied in detail. As a result, the optimum value of iodine content in acetone was 200 mg/l, the applied electrical potential for electrophoresis was 200–300 V for 10 mm electrode gap, and the content of YBCO powder was 10–20 g/l in acetone suspension solution. The critical temperature was determined at 91 K by AC susceptibility curve and the critical current density, J c, was measured by a four-point prove method at the value of 700 A/cm 2 deposited on the Ag coated Al 2O 3 substrate and 1456 A/cm 2 deposited on the Ag wire (77 K, 0 T).