High-temperature YBa2Cu3O7 Research Articles

A Bunch of YBCO Josephson Generators for the Analysis of Resonant Cold-Electron Bolometers

The resonant properties of Cold-Electron Bolometers (CEBs) located at a 0.3 K cryostat plate are measured using a 50 μm long high-temperature YBa2Cu3O7−δ (YBCO) Josephson junction oscillator, placed on a 2.7 K plate of the same cryostat. For these purposes, a bunch of YBCO Josephson oscillators with various lengths of dipole antennas and overlapping generation bands has been developed and investigated in 50–500 GHz frequency range. Two setups of Josephson junction placement were compared, and as a result, various narrow-band receiving systems with CEBs have been measured, demonstrating the feasibility of the presented approach.

Limiting Characteristics of Classical Josephson Detector

Analytical and numerical calculations of limiting characteristics of electromagnetic radiation detectors based on Josephson junctions are carried out. Josephson junctions are described by a simple resistively shunted model and their Josephson energy is considered to be comparable to the energy of thermal fluctuations. The operation modes of such junctions as a classical detector using ac rectification on a static nonlinear current–voltage characteristic are established. The results of numerical and analytical calculations are compared, and it is shown that the classical detection mode can be analyzed and optimized using the derived analytical expressions for the main limiting characteristics. The study demonstrates the possibility of achieving a limiting sensitivity up to 2 × 10–15 W/Hz1/2, a dynamic power range of 105–106, and a spectral range up to 1.4 THz, in a temperature range 50–77 K using new Josephson thin-film junctions consisting of high-temperature YBa2Cu3O7 – x superconductors with mutually tilted c axes.

The Effect of Sintering Oxygen Partial Pressure on a SmBiO3 Buffer Layer for Coated Conductors via Chemical Solution Deposition

The application of high-temperature YBa2Cu3O7−δ (YBCO) superconducting material is a considerable prospect for the growing energy shortages. Here, SmBiO3 (SBO) films were deposited on (100)-orientated yttrium-stabilized zirconia (YSZ) simple crystal substrates via the chemical solution deposition (CSD) approach for coated conductors, and the effects of sintering oxygen partial pressure on SBO films were studied. The crystalline structures and surface morphologies of SBO films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscope (AFM). The optimized growth temperature, the intensity ratios of the SBO (200) peak to the SBO (111) peak, and the crystallinities of SBO films increased with the sintering oxygen partial pressure. The SEM and AFM images displayed a smooth and well-distributed surface in the argon atmosphere. The subsequent YBCO films with superconducting transition temperatures (Tc = 89.5 K, 90.2 K, and 86.2 K) and critical current densities (Jc = 0.88 MA/cm2, 1.69 MA/cm2, and 0.09 MA/cm2; 77 K, self-field) were deposited to further check the qualities of the SBO layer. These results indicated that sintering oxygen partial pressure had an effect on the epitaxial growth of the SBO buffer layer and YBCO superconducting properties. The experimental results may be a usable reference for the epitaxial growth of YBCO-coated conductors and other oxides.

Paramagnetism of copper–oxygen chains in high-temperature YBa2Cu3O6 + δ superconductors

Experimental evidence for the existence of chain paramagnetic Curie-type contributions to the temperature dependence of static magnetic susceptibility χ(T) in the normal (nonsuperconducting) state is obtained for a series of pure YBa2Cu3O6 + δ high temperature superconductors with different oxygen contents (0.6 < δ ≤ 1). It is shown that the chain contribution is obvious on χ(T) curves only in the T < 150K range of temperatures, grows along with the number of oxygen vacancies in Cu1–O4 chains, and depends on the ordering of these vacancies.

Magnetic susceptibility of fine crystalline high-temperature YBa2Cu3O6.93 superconductors. The role of nanoscale structural disordering

Static magnetic susceptibility χ(T) in the normal state (Tc ≤ T ≤ 400 K) and specific heat C(T) near temperature Tc of the transition to the superconducting state are experimentally studied for a series of fine crystalline samples of high-temperature YBa2Cu3Oy superconductor, having y and Tc close to optimal but differing in the degree of nanoscale structural disordering. It is shown that under the influence of structural disordering, there is enhancement of anomalous pseudogap behavior of the studied characteristics and a significant increase in the width of the pseudogap.

Oxygen defects relaxation in high-temperature YBa2Cu3O7 superconductors

The temperature dependences of normal state static magnet susceptibility χ(T) for high-temperature YBa2Cu3O7 superconductors (Tc ≤ T ≤ 400 K) measured for the same sample before and after 22 years of storage are compared. It is shown that during longime storage of a maximally doped sample, its electronic system is more in equilibrium than it was in the initial state, while a similar underdoped sample decomposed completely. Comparing the χ(T) curves for YBa2Cu3O7, we draw conclusions as to the nature of the Curie contribution and the fluctuation-induced contribution to the magnetic susceptibility of the investigated sample, and the experimental procedure for determining Tc.

Photocurrent in superconducting YBa2Cu3O7−x films induced by an infrared free electron laser

Since the discovery of high-temperature cuprate superconductors, there has been much intensive study about the mechanism of them. However, identifying the dynamical mechanism behind them remains one of the great challenges in condensed matter physics. We investigated the high-temperature YBa2Cu3O7−x superconducting films by using a free electron laser (FEL). The method is a type of photoelectron spectroscopy called a free electron laser internal photoemission. The spectrum of the photocurrent induced by FEL was measured in the case of 15K and 100K. We estimated the superconductive gap energy of YBa2Cu3O7−x by comparing the photocurrent spectrum of the superconductive state with that of non-superconductive state.

Study on characteristics of high temperature superconducting magnetic thrust bearing for 25 kW h flywheel

An axial air gap type thrust bearing of the outer diameter of 620 mm for 25 kW h flywheel which combined with the permanent magnet of Nd–Fe–B and 10 pieces of high temperature YBaCuO superconductors of the diameter of 150 mm directly cooled by the refrigerator was fabricated, and its performance tests were conducted. Load capacity which could support a planned rotor weight of 8.2 kN was confirmed, and also the stiffness of the radial direction and the axial direction were measured in case of several initial cooling conditions. Spring and damping coefficients in zero field cooling were also measured in the tapping test, and it was found that axial spring coefficients were about 10 times as large as radial spring coefficients, though damping coefficients were almost the same.

Calculated Spectral Properties of YBa2Cu3O7?? Thin Films

The present paper reports the results of theoretical valence band structure investigations of high-temperature YBa2Cu3O7—δ thin films obtained by calculation of the X-ray emission (XES) and photoelectron (PES) spectra. The XES and PES spectra were obtained on the basis of energy band structure calculations which were realized in the framework of a local density functional approximation using the film linearized augmented plane wave method. The calculated spectra are compared with the experimental data. The main characteristic properties of the experimental spectra are interpreted on the basis of the performed computations.

Preliminary study of working characteristics of film HTS switch in liquid nitrogen

Repetetive switches - new component for superconducting devices - are one of the possible right now applications of high-temperature superconductors (HTSC). High-temperature YBaCuO superconducting films (thickness 0,3 μm, area 15 x 11,5 mm 2) with silver contacts were used as gate elements for switches of periodical action with current and thermal control. Their speed of response, gate characteristics under current control, a range of their working frequencies as dependent on the type of the control pulse and its energy and on the amplitude and porosity of the different-polar power voltage are determined in the liquid nitrogen. Parameters of a superconducting rectifier with above HTSC switches working in liquid nitrogen are given.

Prebreakdown effects and electric strength of high-temperature oxide superconductors

The emissive properties and electric strength of the high-temperature YBaCuO oxide superconductor were investigated in both the superconducting and the normal state. The results show that the emissive properties of YBaCuO cathodes are similar to those of metals. The vacuum pulsed breakdown with YBaCuO electrodes has some features similar to those observed for metallic electrodes. The formation of a dielectric covering on high-temperature-superconductor cathodes makes feasible their application in HV electrophysical devices.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Chemical bonding in high-temperature YBa2Cu3O7 superconductors

Calculations for clusters serving as models for the electronic structure of the copper, barium, and oxygen sites in high-temperature YBa2Cu3O7 superconductors were carried out in the framework of the discrete variation method. An analysis of the bond orders in such compounds was carried out using the overlap occupancies of various AO of the metal and oxygen atoms. Values were obtained for AO occupancies and effective charges on the atoms in the clusters.

XPS studies on passivated and degraded YBa2Cu3O7−x films

High-temperature YBa2Cu3O7 − x superconductors are known to degrade in the presence of moisture. It was shown that the use of certain polymeric materials in solution during processing of the superconductor could passivate the film and reduce degradation in the macroscopic scale. X-ray photoelectron spectroscopy was used to study the surfaces of passivated as well as degraded YBa2Cu3O7 − x samples. In the degraded sample, Y, Ba, Cu and O were present in chemical states other than those expected in superconductors. Segregation of Ba at the surface was also observed. In the passivated sample, superconducting species were retained at the surface despite limited impurity build-up.

Zettl and Kinney reply.

A reply to the comment on oxygen isoptope effect in high temperature YBaCuO perovskite superconductors is presented. (AIP)

Batlogg, Cava, and Stavola reply.

A reply to the comment on oxygen isotope effect in high temperature YBaCuO perovskite uperconductors is presented. (AIP)

Influence of Induced Porosity on Resistivity of YBa2Cu3O7 Superconductors

Preliminary evidences for the existance of a “weak” influence of porosity on the electrical properties of the high temperature YBa2Cu3O7 superconductive ceramics are presened.

Critical Currents in the YBaCuO Compound Superconducting Thin Films

This note contains information on the properties of epitaxial thin films of the high temperature YBaCuO compound superconductors. Some thoughts regarding critical current and mechanisms of vortex pinning are presented. It is suggested that one of the more effective mechanism of pinning is associated with a random distribution of defects which perturb the condensation energy. The defects are on the scale of the coherence length.