Samples Of high-Tc Superconductors Research Articles

SiCサセプターを用いた家庭用電子レンジでのYBa<sub>2</sub>Cu<sub>3</sub>O<sub>y</sub>銅酸化物超伝導体の急速な合成

Nearly single-phase samples of high-Tc superconductors of the Y-123(YBa2Cu3Oy) phase have been prepared using a domestic microwave oven. Since it is significantly important to control temperature of the sample for microwave heating, the samples were placed into thermally insulated box coated with SiC (susceptor). Weighting of Y2O3, BaO, and CuO with a molar ratio were carried out and mixied with agate mortar for 1 hour. Samples (12 mm in diameter) were pressed with mold at 30 MPa and heated by microwave (2.45 GHz, and 700 W) with the susceptor. The temperature in the susceptor was kept at 850 °C for 10 minutes, and the samples of Y-123 were prepared. The produced sample showed superconductive transition temperature (Tc) by 92 K, and had zero resistance by 85 K. These properties for samples prepared by microwave heating were almost consistent with the samples produced by the conventional solid phase process. Properties of Y-123 sintered by various susceptors were mainly investigated. These results showed that microwave sintering was suitable for rapid heat-treatments of a copper oxide superconductor.

Identification of the inverse melting line in the vortex phase diagram of a low Tc superconductor, Ca3Rh4Sn13

We present the vortex phase diagram in a weakly pinned single crystal of a low Tc superconductor, Ca3Rh4Sn13 (Tc ∼ 8.37 K). We believe that a well ordered Bragg glass phase is sandwiched between the multi-domain vortex glass and an amorphous vortex state in a portion of the field–temperature phase space. From an exploration of the thermal variation of the onset of the non-monotonic variation of the critical current density as fingerprinted by the second magnetization peak (SMP) in the magnetization hysteresis loops, we have sketched a phase boundary akin to the inverse melting phenomenon reported earlier only in samples of high Tc superconductors. We reveal here a step change in the equilibrium magnetization across the SMP and peak effect regions, which is a suggestive feature of the first order phase transition. We have determined a lower field limit (like a spinodal line) of the transition to the vortex glass phase via the identification of the SMP anomaly in the ac susceptibility measurements, where shaking of the vortex matter can facilitate the accession of the underlying equilibrium phase.

ＳｉＣサセプターを用いた家庭用電子レンジでのＢｉ系銅酸化物超伝導体の急速な合成

Nearly single-phase samples of high-Tc superconductors of the Bi-2212 phase have been prepared using a domestic microwave oven. Since it is to be important for the preparation to control the temperature of the sample environment, the samples were placed into thermally insulated box whose inner surface is made by SiC. An industrial microwave (2.45 GHz) furnace was used with repeating the microwave radiation processes with intermediate grinding. The comparison among microstructures of the samples obtained by domestic and industrial microwave ovens as well as those of TSFZ single crystals and polycrystals by solid state method was reported.

Nanoscale flux pinning sites in high‐ T c superconductors

Ideal flux pining centres in high-Tc superconductors should be of nanometre size as the coherence length, ξ, is so small. Therefore, the optimisation of high-Tc superconductor samples concerning high critical current densities and high flux pinning has to take place in the nanometre range. An important goal of the current research is to find specific preparation strategies to create such ideal flux pining sites already during the sample processing. By means of AFM and STM measurements at ambient conditions, we have investigated the topographies of various samples of YBa2Cu3Ox (YBCO), NdBa2Cu3Ox (NdBCO), SmBa2Cu3Ox (SmBCO), (Sm,Eu,Gd)Ba2Cu3Ox (SEG) and (Nd,Eu,Gd)Ba2Cu3Ox (NEG) high-Tc superconductors. We find that the two systems with the highest critical current densities (NEG, SEG) and hence, the strongest flux pinning, exhibit microstructures on the nanometre scale which are remarkably different from those obtained in the YBCO system. The stripe-like growth structures observed in our topography measurements may be the key for the considerable improvements concerning the critical current densities especially at high magnetic fields and elevated operating temperature (77 K). (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Critical state in thin anisotropic superconductors of arbitrary shape

A thin flat superconductor of arbitrary shape and with arbitrary in-plane and out-of-plane anisotropy of flux-line pinning is considered, in an external magnetic field normal to its plane. It is shown that the general three-dimensional critical state problem for this superconductor reduces to the two-dimensional problem of an infinitely thin sample of the same shape but with a modified induction dependence of the critical sheet current. The methods of solving the latter problem are well known. This finding thus enables one to study the critical states in realistic samples of high-Tc superconductors with various types of anisotropic flux-line pinning. As examples, we investigate the critical states of long strips and rectangular platelets of high-Tc superconductors with pinning either by the ab-planes or by extended defects aligned with the c-axis.

Rapid Preparation of High-Tc Superconductors of the Bi-2212 Phase Using a Domestic Microwave Oven

Single-phase samples of high-Tc superconductors of the Bi-2212 phase have been prepared using a domestic microwave oven. It is to be important for the preparation to control the temperature of the sample environment and to repeat the microwave-radiation process with intermediate grinding, because the Bi-2212 phase is stable only in a narrow temperature range and requires a long heat-treatment time for formation. The partial substitution of Pb for Bi is also to be effective for the formation of the Bi-2212 phase.

Low-field microwave signal in undoped and Sb-doped Bi-Pb-Sr-Ca-Cu-O

Non-resonant low-field microwave signal in undoped Bi-Pb-Sr-Ca-Cu-O (2223) sample increases monotonously with decreasing temperature, like that in many bulk samples of high-Tc superconductors. But the signal of a Sb-doped sample shows a peak at 103 K, and declines gradually and tends to stabilise when the temperature is further reduced. A distorted 2223 phase (i.e., 130 K phase) which was an intergrowth of 2223 and insulating monoclinic phases in the Sb-doped sample, was unstable, and it might change into the stable insulating monoclinic phase and lost its superconductivity at lower temperatures.

Second harmonic generation as a sensitive technique for estimating H c1 of high T c materials

A simple and interesting technique for measuring the Hc1 of the superconducting grains in bulk high Tc superconductor (HTSC) samples is presented herein. This technique takes advantage of interesting history effects observed in the nonlinear magnetic response of HTSC samples. The hysteretic second harmonic magnetization shows sharp structure at low applied fields due to the magnetic flux trapped inside the grains. This feature is used to track the penetration of magnetic field inside the superconducting granular regions.

Use of a phase-sensitive detector for measuring magnetic hysteresis loops

A method for magnetic hysteresis loop measurement on small samples of high Tc superconductors is described, applicable to other types of magnetic materials as well. It is based on an unusual working regime of the phase-sensitive detector with a square wave mixer signal and controllable reference phase setting. The main advantages of the method are its sensitivity and the possibility of measuring in a wide frequency range. A drawback of the method is that it is fully correct only in the case of a symmetrical hysteresis loop.

Biaxially aligned high T c superconductors

A new technique is described for preparing polycrystalline samples of high Tc superconductors, which should have superior properties for many applications, including potentially much higher critical currents.

Low-field magnetization curves of YBa2Cu3O7−x and BiSrCaCu2O5.5: Effects of Josephson medium

We present the measurement of dc magnetization curve of three samples of high-T c superconductors in relatively low magnetic field of ±50 mT and at temperaturesT=4.2 K andT=77 K by a SQUID susceptometer. The samples were polycrystalline YBa2Cu3O7−x, a single crystal of YBa2Cu3O7−x, and polycrystalline BiCaSrCu2O5.5. We have especially studied the influence of the Josephson medium inside our samples on their low-field magnetization. We have found closed hysteretic loops in the field ±4 mT with “virgin” and “granular” slopes in the sample of polycrystalline YBaCuO and clear flux jumps corresponding to the penetration of low-field (Josephson) vortices. The pinning of these vortices in our case is rather low. In polycrystalline sample of BiCaSrCuO, we have found only reversible magnetization curves corresponding to very low pinning and/or to relatively low number of weak links.

Water reaction of superconducting YBa 2Cu 3O 7 at 0°C and its protection from water corrosion at 100°C

Abstract In this paper the reaction of superconducting YBa2Cu3O7 with water at 0°C is proved true clearly by PH testing of the soaking water and electron microscope analysis of carbonate precipitates of the filtered water, but ambiguously by static susceptibility measurements of the residue. In addition, we found some plastic solution. When the solution was smeared on the superconductor surface a thin film will be formed. The film protects the YBa2Cu3O7 from water and atmospheric moisture corrosion. If necessary, one may dissolve the film again by some organic solvent and the properties of the superconductor remain basically unchanged. The plastic solution and the solvent are of much benefit to save the high Tc superconductor samples in the laboratory.