A. Cigáň

Simplified fast method for magnetic characteristics measurement of the HTc superconducting materials

Abstract A simple measuring method and system for fast measurement of HT c superconductors characteristics are described. The measured sample is inserted into a low-frequency magnetic field in the center of two oppositely oriented coplanar coils with different diameters. The coils together with the sample are placed in the vessel with LN 2 which is outside the LHe cryostat. The currents in the coils are set up in such a way that before inserting the sample the compensated state (zero signal on the system output) is reached in the space of the pickup coil of the SQUID 2nd order gradiometer. After inserting the sample the compensation is disturbed and the arising signal is proportional to the equivalent dipole magnetic moment which characterizes the investigated superconducting material. The experimental measuring system reaching a sensitivity of order 10 -7 A m 2 at a frequency of the magnetizing field ⩽1 Hz is described. Measured magnetization hysteretic characteristics of the short-period melted HT c Bi superconductor are given.

The effect of rare earth oxide substitution on the magnetic properties of Tl-based superconductors

Abstract The effects of the heterovalent substitution of the rare earth ions La3+, Sm3+, Pr3+, Dy3+ and of Y3+ into the Ca2+ separating layers on the magnetic properties of (Tl,Pb)-1223 and (Tl,Pb)-1212 superconductors are reported. Nominal compositions of (Tl0.6Pb0.5)(Sr0.8Ba0.2)2(Ca1−xMx)2Cu3O8+δ, where M=La, Sm, Pr, Dy, Y and x=0.0, 0.05, 0.1, 0.15 and 0.2 were investigated. Increasing contents of the rare earth elements enlarged the superconducting Tl-1212 phase in the samples. This led to a decrease of the Tc values. AC and virgin volume magnetization characteristics of all fabricated samples were measured at 77.3 K in magnetic fields ranging from 10−1 to 105 Am−1. A decrease in the content of the Tl-1223 phase affected the magnetization mainly in the range of stronger fields around 105 Am−1. For the lower substitution levels (x=0.05, 0.1) an improvement of the intergrain links was found.

Influence of the Tl- and Hg-content on magnetic and transport properties of the Pb, Sr-doped Tl-1223 and Hg-1223 superconductors

Abstract The effects of the thallium and mercury content x on the as-sintered and post annealed samples of M x Pb 0.4 Sr 1.6 Ba 0.4 Ca 2 Cu 3 O 8+ δ {M: Tl (0.32≤ x ≤0.74) or Hg (0.18≤ x ≤0.68)} have been studied by magnetization and transport measurements. For Tl-1223 we have found the optimum Tl doping level to be x =0.53 regarding the grain properties, the content of superconducting phase, the first penetration field H pl wl , the transport ( J c tr ), magnetic intergrain ( J c M ) and intragrain ( J c g ) critical current densities. The critical temperature T c of the as-sintered Tl-1223 sample decreased with increasing Tl content. Post-annealing in oxygen improved the T c for Tl contents of x ≥0.53 and had generally positive effects on the critical current densities. The intergrain properties of the Hg-1223 samples were much worse than those of the Tl-based superconductors.

Experimental study of the intergranular weak link structures YBa2Cu3O7−x with the help of magnetization measurements

AC and DC virgin magnetizations of sintered YBa2Cu3O7−x samples have been measured in dependence of the sintering temperature. The samples were prepared by solid state reaction of stoichiometric decarbonated mixture of Y2O3, BaCO3 and CuO components. Magnetization curves were measured at 77K in the range of magnetic field (10−1−2×104Am−1). The temperature of sintering was being changed in the range 910°C up to 950°C. In the range of weak magnetization fields the magnetization curves are affected by properties of the intergranular medium — the intergranular weak links. The parameters H1w1, H2w1 and H1g characterising the flux penetration into intergrain and intragrain medium were estimated from the magnetization measurements.

Effects of low-level La doping and ageing on TlPb-1223 high T c superconductors

Bulk samples of the nominal composition of (Tl0.6Pb0.5)(Sr0.8Ba0.2)2Ca2Cu3O8+δ−xLaO1.5 (x = 0–0.1) were prepared by using two-step process and their microstructure, Tc values, and magnetization were studied. The samples consist of the Tl-1223 dominant phase with small Tl-1212 admixture, which increases with a rise of La content. Five years ageing and following oxygen annealing at 450°C and subsequently at 750°C have only a modest effect on Tc values of the studied samples. Low-level La doping (x = 0:04) leads to an increase of Tc values by about 2 K in comparison with undoped samples. Oxygen annealing at 750°C results in an increase in the volume magnetization hysteresis in low applied magnetic fields and rise of critical current density at zero magnetic field and 77 K. This effect is most pronounced for the low La doped sample with x = 0.04. Changes of the induced voltage, U originating in the Meissner effect and of its harmonics in dependence on temperature were measured and used for characterization of the temperature distribution of inter-grain junctions.

Study of light nonstoichiometry in Eu-Ba-Cu-O systems

We studied effects of light Eu-Ba nonstoichiometry in Eu-Ba-Cu-O superconducting compounds on their transition, structural, and magnetic properties. Two series of Eu1+xBa2-xCu3O7+δ and Eu1-x Ba2+xCu3O7+δ samples with x = 0, 0.01, 0.02, 0.04, 0.05, 0.07 and 0.1 were synthesized by the solid-state reaction method from Eu2O3, BaCO3 and CuO precursors and sintered at 1050°C for 72 h in flowing oxygen. Structural, transition, and magnetic properties were investigated by means of X-ray diffraction, resistance, mutual inductance, magnetization and optical measurement methods. The Eu-Ba nonstoichiometry in the two series results in different effects on transport, magnetization, grain, intergrain and microstructure properties of the samples in relation to the substitution level of x. All the samples show the values of critical temperature Tc, volume density ρ, and maximum volume magnetization Mmax higher than 91 K, 6.4 g cm-3 and 104Am1, respectively.

Preparation of bismuth-doped yttrium iron garnets and their characterization

This paper presents the study of bismuth-doped yttrium iron garnets with composition Y3-xBixFe5O12 (Bi: YIG) prepared by sintrating of metal oxides for various sintrating conditions (times, temperatures, etc.). The structure of the samples was characterized by XRD patterns. The spectra, obtained by LIB (Laser Induced Breakdown) method that is based on the interaction of high power laser beam with studied medium, are also presented. Breakdown and following ablation were induced on the sample surface in air by focusing mode-locked Nd: YAP laser radiation. The laser-induced spectra for various bismuth-donated samples and metal oxides are compared.

Microstructure and superconducting properties of melt textured Y–Ba–Cu–(Ag)–O composites with various Ag content ☆

Abstract The effects of silver doping on microstructure and magnetic properties of YBa 2 Cu 3 O 7− x melt-textured samples prepared by the quench and melt growth technique were studied. Silver was added in the form of Ag 2 O in the range of 0–10 wt%. The increasing silver doping level up to the level of 1.0 wt% Ag 2 O of YBa 2 Cu 3 O 7− x samples results in remarkable improving of their magnetic properties, texturation and porosity. For the given processing conditions, the superconducting properties strongly decrease for the higher doping levels of 5.0 wt% Ag 2 O and more. In our case in reaction systems with higher content of silver doping, which remarkably depresses the formation temperature of the superconductor phase, the texturation process was not completed. The best developed texture as well as the highest magnetisation and first penetration magnetic field showed, under our experimental conditions, the sample containing 1 wt% Ag 2 O.

Substitution and doping of YBa2Cu3O7 by Agn+, Sr2+, Sc3+ and related properties

Abstract We investigated two series of samples of YBa 2 Cu 3− z Sc z O 7− δ prepared at the sintering temperature 967 and 980°C and the two series of YBa 2− y Sr y Cu 3 O 7− δ –Ag 2 O systems differing in silver doping with 2 and 10 wt% Ag 2 O by X-ray diffraction, resistive and detailed magnetization measurements. Doping levels of Sc, Sr and Ag 2 O range from z =0 to 1.0, y =0.0 to 1.0 and Ag 2 O (2 and 10 wt%), respectively. For all doping levels y , z and silver oxide the superconducting phases at 77.3 K were observed. For the higher Sc content z , a deterioration of the critical temperature ( T c ), the density, the volume fraction of superconducting phase, as well as the volume magnetization (magnitude) M , the volume magnetic susceptibility, the first magnetic penetration field ( H p1 ) and the slope of magnetization loops of the samples were observed in relation to sintering temperature. Increasing Sr content results in gradual decreasing of superconducting properties: T c , H p1 , and M , the slope of magnetization loops and magnetization hysteresis, they all decrease with increasing Sr content at higher Sr levels.

Influence of high level Ag doping on the superconducting properties of YBa2Cu3O7/Ag composites☆

Abstract The role of Ag-additions in the synthesis of bulk YBa 2 Cu 3 O 7 is extremely varied. In order to separate and understand some aspects of these introductions, this paper describes the synthesis of two series of bulk samples with different thermal histories as a function of their silver content up to very high loadings (0–80 wt.%), which may have industrial significance. Their morphological and thermal characteristics are discussed and their superconducting properties are studied in detail using AC and DC susceptometry at high and low field. They exemplify the role of silver as flux at high temperatures and as mediator of oxygen transport at lower temperatures.