Distributions of Y2Ba1Cu1O5 particles in fluorine-doped Y1Ba2Cu3O x superconductors

An experimental study has been carried out on the relationship between Y₂Ba₁Cu₁O₅ particles in Y₁Ba₂Cu₃O _x superconductors and electric furnace cooling rates. As the electric furnace cooling rates decrease, the Y₂Ba₁Cu₁O₅ particles become uniformly disperse in fluorine-doped Y₁Ba₂Cu₃O _x superconductors. However, the Y₂Ba₁Cu₁O₅ particles do not appear in the undoped Y₁Ba₂Cu₃O_x superconductors.     

AC losses in Y1Ba2Cu3O7−δ:Ag tapes

The frequency dependence of ac losses of a superconducting tape consisting of Y₁Ba₂Cu₃O_7-δ material in a silver sheath was measured from 50 Hz to 50 kHz using a four-probe technique developed and reported earlier. Contrary to expectation, the ac losses were found to have a frequency-independent regime in the loss spectrum. A tentative explanation has been offered to account for the frequency-independent loss.     

Y3Ba5Cu8Ox Superconductor Under Hydrostatic Pressure

Journal of Low Temperature Physics - Superconducting Y3Ba5Cu8O18 samples were prepared by standard solid-state reaction method in comparison with Y1Ba2Cu3O7 sample. Resistance vs. temperature of...     

The Effect of Y2O3 on AC Susceptibility Measurements of MPMG YBCO Superconductor

In this study, two kinds of melt-powder-melt-growth (MPMG) YBCO sample grown on a buffer layer of Y₂O₃ addition were fabricated. The compacted powders were located on a crucible with Y₂O₃ powder freely poured and a buffer layer of pressed Y₂O₃. AC susceptibility measurements of the samples as a function of temperature was reported for several different AC magnetic-field amplitudes (H _ac ) in the presence of static bias magnetic field (H _b ) directed along H _ac . The loss peaks are found to shift towards lower temperatures as the AC field strength is increased. The frequency effect on the AC susceptibility was also measured. As the frequency increases, the peak temperature shifts to higher temperature. This effect can be interpreted in terms of flux creep.     

Superconducting Fluctuations in Polycrystalline Y3Ba5Cu8O18

The Y₃Ba₅Cu₈O₁₈ superconductors are synthesised using the solid state reaction method under different annealing conditions. Structure characterisation using X-ray diffraction shows that the lattice parameters are different from those of the standard YBCO system. The resistivity measurements are performed using the four-probe method in the temperature range from 77 to 300 K. The electrical resistivity indicates the transition temperature T _c (O₂)=100.2 K and T _c (air)=92.3?K. Thermal fluctuations were experimentally studied. The correlations of the critical exponents with the dimensionality of the fluctuation system for each Gaussian regime were performed using the Aslamazov-Larkin theory. Near T _c , a critical regime with a critical exponent of λ _CR=0.35 is effectively described by the E-model.     

Investigation of Y1Ba2Cu3O6.9 and Er1Ba2Cu3O6.8 during cyclic temperature variations

Gravimetric investigations of the superconductive ceramics Y₁Ba₂Cu₃O_6.9, Y₁Ba₂Cu_2.7Al_0.3O_7.1 and Er₁ Ba₂Cu₃O_6.8 during cycling heating cooling in the interval 293–1323 K at partial pressure of the oxygen 0.02 and 0.2 × 10⁵ Nm^–2 are presented. Intervals of intense weight changes during heating and cooling are determined. Oxygen loss was shown to be the main reason for the weight changes. Structural characteristics and resistivity of the yttrium ceramics in the above-mentioned temperature interval are investigated. Experimental data are discussed within the framework of the models of the quasi-equilibrium and essentially nonequilibrium processes. Binding energy and diffusional parameters of the evolving gas are estimated.     

Superconducting Y1Ba2Cu3O7-y thick films from nitrate pastes

A novel technique for forming superconducting Y₁Ba₂Cu₃O_7-y , thick films by screen printing pastes made from spray-dried nitrate powders on alumina and magnesia is described. Manufacture and characterization of nitrate powders are discussed. A model based on dissolution of yttrium nitrate is proposed to explain the rheological and film-forming properties of the nitrate pastes. Low-viscosity pastes are found to give better performance in terms of printability and quality of prints. Barium carbonate formation can be avoided by use of the nitrate pastes and by firing in an oxygen atmosphere. Superconducting thick films were achieved on single-crystal (1 0 0) MgO (T ₀=77 K) and on polycrystalline alumina with a prereacted barrier layer (T ₀=55 K).     

Magnetic Field- and Frequency-Dependent Study of the AC Susceptibility of High-Tc YBCO Single Crystal

Journal of Superconductivity and Novel Magnetism - The temperature dependence of AC susceptibility (ACS) has been measured for a very high-quality plate-like slightly overdoped YBCO single crystal...     

Magnetoresistance Study of Y3Ba5Cu8O18 Superconducting Phase Substituted by Nd3+ and Ca2+ Ions

Superconducting samples of type Y_3?x Nd _x Ba_5?x Ca _x Cu₈O₁₈ with 0.0 ≤ x ≤ 0.4 have been prepared via the solid-state reaction technique. The prepared samples were characterized using X-ray powder diffraction (XRD) technique for phase analysis. The elemental content of the prepared samples was determined using particle-induced X-ray emission (PIXE). In addition, the oxygen content of these samples was obtained using non-Rutherford backscattering spectroscopy (RBS) at 3 MeV proton beam. The results indicate that these substitutions do not affect the orthorhombic structure, while they decrease the oxygen content of Y-358 phase. The electrical resistivity of the prepared samples was measured by the conventional four-probe technique from room temperature down to the zero superconducting transition temperature (T ₀). A slight change in the superconducting transition temperature (T _c) is observed for 0 ≤ x ≤ 0.1, and then it decreases linearly with further increase in x. The linear decrease in T _c is attributed mainly to the partial substitution of Ba²⁺ ions by Ca²⁺ ions rather than the partial substitution of Y³⁺ ions by Nd³⁺ ions. The effect of magnetic fields up to 4.44 kG on the electrical resistivity has been studied to investigate the vortex dynamics for the prepared samples. The experimental data, in the second stage of superconducting transition, fit well with the thermally activated flux creep (TAFC) model, and the activation energy U(B) shows a power law dependence on magnetic field as B ^?β . Also, the transition width is related to the magnetic field according to the relation ΔT α B ⁿ . The values of β and n are strongly dependent on the Nd³⁺ and Ca²⁺ ion substitution. The magnetic field and temperature dependence of the activation energy U(B, T) is found to be U(B, T)? ΔT B ^?η , where η = β + n. Furthermore, the critical current density at zero temperature, J _c(0), as a function of the applied field was calculated for all the prepared samples. The result shows an enhancement in J _c(0) of Y-358 phase at x equals 0.4 at different applied fields.     

Growth and characterization of evaporated thin films of Y1Ba2Cu3Ox

We have prepared thin films of Y-Ba-Cu-O by coevaporation in the presence of oxygen onto room-temperature substrates, followed by postannealing in oxygen. Films have been grown on (100) SrTiO₃, (100) MgO, and LiNbO₃. The films have been characterized by electrical resistivity, X-ray diffraction, and elastic backscattering (EBS) measurements.     

Thermogravimetric studies of Y1Ba2Cu3O7−x superconductors

The synthesis conditions and oxygen stoichiometry were determined using a thermogravimetric analyser. The kinetics of oxygenation at different temperatures and at different atmospheres were studied. The oxygenation kinetics were found to be sensitive to porosity of the material. The appropriate oxygenation temperature was found to be 400 °C. For oxygenation temperatures below 400 °C, the oxygenation occurs by a nucleation and growth process, whereas for higher temperatures it is diffusion limited.     

High-capacity superconducting current leads of Y1Ba2Cu3O7−x

We have fabricated and measured a high-capacity superconducting current lead composed of a Y₁Ba₂Cu₃O_7?x cylinder, 20 cm long and 0.9 cm² cross section. A steady-state, d.c., critical current of 225 A at a temperature of 77 K was measured in this sample, using a voltage criterion of 2×10^?7 V/cm (p = 8×10^?10 ohm-cm). This current was limited by the currentinduced, self magnetic field. To our knowledge this is the largest d.c. critical current so far reported in a Y₁Ba₂Cu₃O_7?x sample and demonstrates the possibility of using hightemperature superconducting HTS materials for current leads to low-temperature superconducting LTS magnets or in power distribution systems.     

Effect of silver in Y1Ba2Cu3O7−x samples

Two techniques for preparing Y-Ba-Cu-O/Ag specimens are presented: (a) solid-state reaction, and (b) normal precursors dissolved in hot concentrated nitric acid and dried in air. The samples are characterized by scanning electron microscopy (SEM), scanning Auger, X-ray diffraction, optical microscopy and electrical resistivity measurements. In comparison with a normal 1-2-3 superconductor it was found that the normalized resistance [R(T)/R(280 K)] decreases for both preparation methods. The material retained a high initial temperature of superconductivity, T _c, for a maximum of 6% w/o Ag₂O during solid-state reaction and 6.5% w/o Ag₂O for samples dissolved in hot concentrated nitric acid and dried in air.     

The Role of Oxygenation on Superconducting Properties of RE3Ba5Cu8O18 (RE=Y, Sm and Nd) Compounds

This study reports the effects of oxygenation on new high-T _c cuprates having the structure of RE₃Ba₅Cu₈O₁₈ (RE=Y, Sm and Nd) and T _c (on) values of 96.5–97.5 K. The measurements have shown that excess oxygenation has no important contribution to the T _c (on) values, but it improves T _c (off) values significantly. From these three systems, RE = Nd is the most sensitive one to the oxygenation. Its T _c (off) value increases by 13 K (from 78 K to 91.1 K) with post-annealing.     

Resistive and magnetic properties of Y1−x Zr x Ba2Cu3O7−δ and Y1−2x Zr x Eu x Ba2Cu3O7−δ superconductive compounds

The results of X-rays, electrical resistivities and magnetic studies performed on Y_−x Zr _x Ba₂Cu₃O_t7−δ and Y_1−2x Zr _x Eu _x Ba₂Cu₃O_7−δ superconducting compounds, in the temperature range 4.2–500 K and external fields up to 50 kOe are reported. The presence of zirconium decreases the superconducting transition temperatures,T _c. BelowT _c, the hysteresis loops narrow when the zirconium content increases. From the magnetization curves, the critical current densities were determined. A time dependence of the magnetizations of logarithmic form was found. The flux-pinning energy was estimated to beU ≃0.03 eV. Above the transition temperatures, Y_−x Zr _x Ba₂Cu₃O_t7−δ samples show a Pauli-type paramagnetism, while Y_1−2x Zr _x Eu _x Ba₂Cu₃O_7−δ compounds have, in addition, temperature-dependent contributions to the magnetic susceptibilities. The effective europium moments are ∼3.40 μ_B suggesting that the ion is in (+3) valence state.