Role of interdomain and interplatelet boundaries on magnetic flux penetration in melt grown YBCO
TL;DR: In this article, a lock-in flat-band detection technique was employed to detect the presence of random domains with aligned platelets separated by microcracks inside the domains, and the results showed an enhancement in H/sub c1/ due to melt processing.
Abstract: The microstructure of a melt processed YBCO sample reveals the presence of random domains with aligned platelets separated by microcracks inside the domains. The lower critical field (H/sub c1/) and critical current density (J/sub c/) of these boundaries will be less than that of the grains, and their role in determining the bulk properties cannot be neglected. We have employed a sensitive lock-in flat-band detection technique and recorded the low field ac M-H loops at 33 Hz and 77 K and derived the flux profiles. The results show an enhancement in H/sub c1/ due to melt processing. Inclusion of Y/sub 2/BaCuO/sub 5/, and Ag enhances the H/sub c1/ further. The flux profiles show distinct slope changes at certain fields which reflect different coupling strengths of weaklinks that become operative for flux entry at different applied fields. While the low field flux profiles are found to reflect the effect of residual weaklinks (like liquid phase and micropores) and domain boundaries, those at higher fields might reflect the effect of platelet boundaries.
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TL;DR: In this article, a melt-textured growth of polycrystalline YBa2Cu3O7−δ superconductor using directional solidification created an essentially 100% dense structure consisting of long, needle- or plate-shaped crystals preferentially aligned parallel to the a-b conduction plane.
Abstract: Melt‐textured growth of polycrystalline YBa2Cu3O7−δ superconductor using directional solidification created an essentially 100% dense structure consisting of long, needle‐ or plate‐shaped crystals preferentially aligned parallel to the a‐b conduction plane. The new microstructure, which completely replaces the previous granular and random structure in the sintered precursor, exhibits dramatically improved transport Jc values at 77 K of ∼17 000 A/cm2 in zero field and ∼4000 A/cm2 at H=1 T (as compared to ∼500 and ∼1 A/cm2, respectively, for the as‐sintered structure), with the severe field dependence of Jc (‘‘weak‐link’’ problem) no longer evident in the new melt‐textured material. The improvement in Jc is attributed to the combined effects of densification, alignment of crystals, and formation of cleaner grain boundaries. Microstructure and distribution of various phases present in the melt‐textured material are discussed in relation to the superconducting properties.
745 citations
"Role of interdomain and interplatel..." refers methods in this paper
...In the case of YBa Cu O - it has been found that the melt processing technique and addition of YBaCuO (211) and Ag [1]–[3] results in an alignment of the grains, improvement in the coupling strength between the grains, and enhancement in the current density by two to three orders of magnitude....
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TL;DR: A liquid phase processing method for the fabrication of bulk YBa2Cu3Ox superconductors with large current carrying capacity has been developed in this paper, where a cooling rate of 1'°C/h in this temperature range has yielded a microstructure with long plate type, thick grains oriented over a wide area.
Abstract: A liquid phase processing method for the fabrication of bulk YBa2Cu3Ox superconductors with large current carrying capacity has been developed. Slow cooling through the peritectic transformation (1030–980 °C) has been shown to control the microstructure of these superconductors. A cooling rate of 1 °C/h in this temperature range has yielded a microstructure with long plate type, thick grains oriented over a wide area. Current density up to 18 500 A/cm2 has been obtained by continuous direct current measurements and in excess of 62 000 A/cm2 with pulse current of 10 ms duration and 75 000 A/cm2 using 1 ms pulse. The strong magnetic field dependence observed in sintered bulk 1‐2‐3 superconductors is also minimized to a large extent where a current density in excess of 37 000 A/cm2 is obtained in a field of 6000 G.
705 citations
TL;DR: In this paper, the critical current density in oxide superconductors is achieved by growing a superconducting phase unidirectionally and suppressing second phase intrusion, leading to the production of well textured YBa2Cu3Ox which yields a high Jc value in the presence of magnetic fields.
Abstract: We report a new process which promises high critical current density in oxide superconductors. The process consists of three stages. Firstly a YBa2Cu3Ox sample is rapidly heated and quenched from the Y2O3 plus liquid region. Subsequently the quenched sample is reheated to the Y2BaCuO5 plus liquid region, and then slowly cooled with a temperature gradient in flowing oxygen. The process enables us to grow a superconducting phase unidirectionally and to suppress the second phase intrusion, leading to the production of well textured YBa2Cu3Ox which yields a high Jc value in the presence of magnetic fields. It is also found that Bean's critical state is realized in such high Jc samples.
692 citations
"Role of interdomain and interplatel..." refers methods in this paper
...In the case of YBa Cu O - it has been found that the melt processing technique and addition of YBaCuO (211) and Ag [1]–[3] results in an alignment of the grains, improvement in the coupling strength between the grains, and enhancement in the current density by two to three orders of magnitude....
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01 Jan 1993
268 citations
"Role of interdomain and interplatel..." refers background in this paper
...microstructure of a melt grown sample reveals a randomdomain-like structure with aligned platelets inside each domain [4], and the platelets are separated by microcracks....
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TL;DR: In this paper, the susceptibility of type II superconductors in low-frequency alternating current fields has been measured using a phase sensitive detector and the response is linear at low amplitude and is consistent with a model based on the reversible oscillation of vortices in harmonic wells.
Abstract: The susceptibility of type II superconductors in low-frequency alternating current fields has been measured using a phase sensitive detector. Penetrations of magnetic field of between 300 A and 500 μm can be measured and if it is assumed that a critical state exists the field profile across the specimen can be plotted on this scale. The response is linear at low amplitude and is consistent with a model based on the reversible oscillation of vortices in harmonic wells. It is not consistent with the signal predicted from `flux creep'. The effective potential wells are found to be harmonic up to their edges and only about 25 A in radius. The resolution is sufficient to show that the surface current is not a critical state, but can be described by a single row of vortices pinned by the boundary of the specimen.
237 citations
"Role of interdomain and interplatel..." refers background or methods in this paper
...The normalized penetration depth is given by [8]...
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...From the peak value of magnetization, the flux profiles are constructed using a procedure [7] developed based on Campbell’s technique [8]....
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