HTSC Ceramics Research Articles

Excess conductivity of HTSC ceramics YBa2Cu3O7–δ with TiO2 impurities

In this work, the conductivity of YBa2Cu3O7−δ ceramics doped with Ti was studied. It is shown that the introduction of the TiO2 impurity leads to an increase in the number of effective scattering centers for normal carriers. The excess conductivity of the studied samples in a wide temperature range obeys an exponential temperature dependence, and near Tc it is satisfactorily described by the Aslamazov–Larkin theoretical model. In this case, the addition of Ti leads to a significant expansion of the temperature interval for the existence of excess conductivity in the ab plane.

Плазмохимический синтез YBa2Cu3O7–y / CuO гранулярных композитов

The possibility of synthesizing HTSC ceramics in the reaction chamber of a plasma-chemical reactor is shown. The method allows one to significantly reduce the process of solid-phase synthesis and obtain modified HTSC ceramics with a given content of non-superconducting additives that act as pinning centers.

Features of the Elastic Properties of HTSC Ceramics in the Transition Zone to the Superconducting Phase

The article presents the results of studies of the elastic properties of the YBa2Cu3O(7 –x) high-temperature superconducting ceramic in the vicinity of the phase transition to the superconducting state at a temperature of 91.3 K and room temperature of 293 K. Near the phase transition temperature with a width of ~10 K, a local increase in longitudinal nonlinear acoustic parameter N was revealed for the first time, which characterizes anharmonic interatomic interaction in the material. Experimental studies of the linear and nonlinear elastic properties of the YBa2Cu3O(7 –x) HTSC ceramic near the superconducting transition zone show that the electronic phase transition significantly influences its elastic properties.

Synthesis and Properties of Bi-HTSC synthesized on the basis of precursors obtained by melt quenching

The article presents the research results on the synthesis of HTSC ceramics using concentrated radiant radiation. It was established that all synthesized samples of the nominal composition Bi17Pb03Sr2Can-1CunOy(n = 3, 4, 5), the main phase was the superconducting phase Bi17Pb03Sr2Can-2CunOy, which has a critical temperature of the transition to the superconducting condition of 107 K. Also in samples of nominal compositions Bi1,7Pb0,3Sr2Can-1CunOy (n = 4, 5) showed traces of phases with higher Tc.

Development of methods for processing spectra of multiple small-angle neutron scattering

A method has been developed for processing spectra of multiple small-angle neutron scattering (MSANS) to obtain information about substance heterogeneities, namely, their size and concentration. A method has been proposed for constructing the dependence of the MSANS line width on the sample thickness starting from the angular neutron distribution measured for one sample. The standard method for processing this dependence has been improved for application at any scattering multiplicity and complete account for the instrumental line of the double-crystal spectrometer. The method has been tested for the MSANS spectra of the samples of the Fe-Ni ferromagnet, Al powders, and HTSC ceramics.

ChemInform Abstract: Sintering and Expansion of HTSC Ceramics

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Sensitive element of magnetometer based on bismuthic HTSC ceramics with a Josephson medium

The technology of obtaining ceramic Bi-Pb-Sr-Ca-Cu-Fe-O HTSC with reproduced properties of a Josephson medium is elaborated. The possibility of creation of the magnetometer with a sensitive element on HTSC ceramics is considered, using a sensitive method of contactless measurements based on the tunnel-diode self-generator. The steepness of the frequency-field behavior is determined, which is one of the main parameters determining the possibility of the HTSC sample’s application in magnetometers, as well as the value of the critical field of hypervortices penetration.

Penetration of weak magnetic field into Bi-Pb-Sr-Ca-Cu-Fe-O HTSC ceramics

The behavior of ceramic HTSC Bi-Pb-Sr-Ca-Cu-Fe-O with the Josephson medium within the range of magnetic fields H = 0–600 mOe under the conditions of compensation for the Earth’s magnetic field is investigated experimentally. The fields describing the phases of successive penetration of hypervortices and Josephson’s vortices into a sample and the dependence of the penetration field H cl on the orthogonal biasing magnetic field are determined. The obtained results are interpreted within the framework of the commonly accepted model of a Josephson medium and the model that gives the averaged description of the behavior of non-identical Josephson contacts.

Locally frozen magnetic field in HTSC ceramics

The value of a locally frozen magnetic field in a region with a diameter of 0.5 mm in a 0.5-mm-thick YBa2Cu3O7-x plate was investigated as a function of the excitation field (to 2x10^4 A/m), plate cooling mode (in the absence or presence of a field; i.e., zero-field cooling (ZFC) or field coupling (FC)), and local demagnetizing field. Analysis of the measurement results in the noted range of excitation fields showed the following: (i) the dependence on the excitation field for the ZFC mode is explained by the local inhomogeneity of critical currents of weak links in the ceramic Josephson medium and is limited by their maximum value at the temperature of the experiment (77 K); (ii) the dependence on the excitation field for the FC mode contains a portion of the magnetic phase transition from the frozen current structure, typical of the initial portion of the dependence, to the current structure characteristic of the ZFC freezing mode, and is limited by this transition; and (iii) the dependence on the demagnetizing field for the ZFC mode can be explained by the stable coexistence (without annihilation) of microscopic current loops with opposite current directions in the ceramics.

Calculation of thermal processes upon the laser modification of HTSC ceramics aimed at increasing the critical current

A mathematical model for the heating of a surface layer of HTSC ceramics by a CW laser beam scanned at a constant rate is considered. The calculated depths of the molten region are presented for the heating of the Bi(2223) ceramics by a CW CO2 laser. The theoretical results are in reasonable agreement with the experimental data. The calculations can be used for the optimization of laser processing of superconducting ceramics aimed at increasing the critical current density.

Spatial inhomogeneity of conductance in HTSC ceramics

Experimental studies of electrical conduction of YBa 2Cu 3O 7− x ceramics near its critical state have been carried out by the method of laser point heating. It has been established that near the transition to superconducting state the conductivity of the ceramics shows a cluster character. The topology of the superconducting cluster and its spatial localization in the specimen have been studied.

Critical current density and induced magnetic field in ceramic superconductors

It is shown that the transport critical current density in HTSC ceramics and induced magnetic field are homogeneous functions of coordinates. The dependence of the critical current density in HTSC ceramics on the magnetic field is reported.

Granular‐percolative superconductivity in organic materials: comparison with HTSC ceramics

AbstractWe report investigations of the low temperature (2 K < T < 15 K) ac susceptibility and the magnetization of the fully deuterated organic superconductor κ‐(BEDT‐TTF)2Cu[N(CN)2]Br. Our measurements were performed after successive annealing at high temperature in the region 65 K < Ta < 110 K where the ethylene molecules undergo some kind of order disorder transition. The annealing time ta was varied from few seconds to about 2 × 106 s. The superconducting state can be described by a distribution of percolating clusters grown during annealing in the transition region. The spatial structure of such clusters and their relaxation times (in the transition region) obey essentially the same scaling laws and the same stretched exponential relaxation as in Ising spin glasses. The data are described by a granular model in which the grain radius r is equal to the average radius of the clusters. At the lowest fields and temperatures the clusters are coupled via Josephson junctions. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A photo-thermally stimulated exoemission technique used to study the properties of HTSC ceramics based on YBa2Cu3O7−δ

The method of photo-thermally stimulated exoelectron emission (PTSE) is used to study the processes in the surface layers of HTSC ceramics based on YBa2Cu3O7−δ. A correlation is observed between variations of the exoemission current and the transition to the superconducting state. The experimentally detected hysteresis in the PTSE intensity of YBa2Cu3O7−δ ceramics, when thermally cycled in the range T=80–160 K, is limited by two processes. Below T=90 K, the chemisorption has a significant effect on the physical phenomena under study, thus impeding the search for new PTSE regularities in HTSC ceramics. At the same time, exoemission properties of the ceramics considerably change in the range 80–160 K. It is also shown that the superconducting transition and the thermal absorption phenomena for an YBa2Cu3O6.8 specimen are split in the studied temperature range, which allows the PTSE technique to detect the superconducting state and to observe the transition dynamics.

Large magneto-resistance of high- TC superconductor based composites to low magnetic fields at the liquid nitrogen temperature

The magneto-resistive effect in bulk 123YBCO + CuO and YBCO + Normal metal BaPbO 3 composites prepared by fast backing technique has been studied. The composites exhibit broadening of resistive transition in low magnetic fields (less than 200 Oe) for a wide temperature range. Experimental dependences of resistivity versus magnetic field at various transport current densities are presented and discussed. The HTSC based composites exhibit a much higher sensitivity to weak magnetic fields at liquid nitrogen temperature, as compared to that for the “pure” HTSC ceramics. This effect is attractive for possible practical applications and may be used in magnetic field sensor devices.

Enhancement of the critical current density in HTSC ceramics by laser radiation

The experimental data on the application of laser radiation to melting YBCO(123) and Bi(2223) high-temperature superconducting ceramics aimed at the improvement of their structure and an increase in the critical current density are systematised. The short-term melting of this ceramics by CO2 laser radiation and the subsequent annealing lead to the formation of a dense fine-grained structure. As a result, the critical current density significantly increases. The best results are obtained for the Bi(2223) ceramics: the critical current density increases by a factor of 40 and 8 at T= 20 K and 77 K, respectively.

Negative magnetoresistance in granular HTSC with trapped magnetic flux

Magnetoresistive properties of Bi-based ceramic HTSC with trapped magnetic flux are investigated at the temperatures near superconducting transition. The effect of trapped field and transport current values and orientations on the field dependence of magnetoresistance ΔR(H) is studied. It is found that for the magnetic field parallel and the current perpendicular to trapping inducing field the dependence ΔR(H) is non-monotonic and magnetoresistance turns out to be negative for small fields, H<Hinv. The magnetoresistance sign inversion field Hinv and the maximum value of negative magnetoresistance increase a little superlinearly with the trapped magnetic field and decrease somewhat with transport current. The results are explained in the framework of model of magnetic flux trapping in grains or superconducting loops embedded in weak links matrix.

Improvement of HTSC-materials by treatment with laser

The influence of different kinds (Nd, ruby and CO 2) of laser radiation on HTSC (Y-123, Bi-2212, Bi-2223) ceramics are shown. Irradiation of HTSC leads to modification of the near-surface layers, by processes such as ceramic densification, granular melting and the appearance of continuous melting with increasing laser irradiation energy. On the whole, the density and smoothness of the surface were improved and content of carbon was minimised with the help of radiation and subsequent thermal treatment. The current density has higher values (>500 A/cm 2) than those which were achieved before the laser treatment (20–340 A/cm 2).

Magnetic flux trapping and broken Abrikosov vortices in yttrium HTSC ceramic samples

Direct evidence of the existence of broken Abrikosov vortices is obtained from measurements of the distribution and values of residual magnetic fields in ceramic yttrium HTSC samples after the switching off of a transport current. In this case, the intergrain magnetic induction averaged over the sample volume has the same direction as the field that was in the sample before the current was switched off.

Effect of an electric field on the I–V curves of DyBa2Cu3−x Oy/1 wt % Pt HTSC ceramics

This paper reports on an experimental study of the effect of a magnetic field, B≤70 G, and an electric field, E=120 MV/m, on the critical current I c and I–V curves of DyBa2Cu3−xOy HTSC ceramics (x=0 and 0.2), both undoped and doped with 1 wt % Pt. It has been established that, in stoichiometric ceramics (x=0) at 77 K, I c drops sharply (by more than an order of magnitude) already at very low B I c . In the case of DyBa2Cu2.8Oy/Pt, the electric field practically does not affect I c but R decreases for I>I c . In a sample placed in a magnetic field, the magnitude of the E effect is observed to correlate with the I c (B) dependence. In particular, in Pt-doped samples, the E effect decreases with increasing magnetic field B not gradually but with a maximum appearing at B ≈10 G, i.e., in the region of the peak effect in the I c (B) dependence. The data obtained suggest the conclusion that the electric-field effect in ceramics exhibiting weak links of the superconductor-insulator-superconductor (SIS) type correlates with magnetic vortex pinning.