Influence of calcining temperature on critical current density of Ag/Bi2223 tapes

2212 intergrowths in the (Bi, Pb)2223 phase have been investigated using in situ high temperature synchrotron XRD technique. With a high energy synchrotron x-ray and high resolution diffractometer, we could obtain high resolution powder XRD patterns of (Bi, Pb)2223 and (Bi, Pb)2212 from the whole bulk inside the Ag-sheath. This gave us more detailed information on 2212 intergrowths in the (Bi, Pb)2223 phase than ever before. During in situ observation, the Ag-tubed precursor was kept at 1095 K with flowing Ar-7.8% O 2 mixed gas. The profiles of the diffraction peaks were analysed by Rietveld analysis to evaluate the isotropic and anisotropic lattice strain of (Bi, Pb)2223 and (Bi, Pb)2212. Considering the evolution of anisotropic lattice strain during the heat treatment, it was concluded that 2212 intergrowths in the (Bi, Pb)2223 phase are not in the untransformed region of (Bi, Pb)2212 after incommensurate intercalation, but a stacking fault-like defect contained in the (Bi, Pb)2223 phase during its nucleation and growth. A new model of 2212 intergrowth formation in the (Bi, Pb)2223 phase was suggested and discussed.

Section: Introductionmentioning

confidence: 99%

In situobservation of 2212 intergrowths in the early stages of (Bi, Pb)2223 phase formation using the synchrotron XRD technique

Nakao

Osamura

2005

“…In particular, the control of phase and structure evolution in the tapes is a key factor for realizing high critical current density (J c ). Therefore, in efforts to achieve a high J c for a (Bi, Pb)2223 tape, the relationship between the phase evolution and heat treatment conditions have been carefully investigated in recent years [1][2][3]. Recently, the post-annealing process has had attention paid to it because of its remarkable effect of increasing J c for the (Bi, Pb)2223 tape [4,5].…”

Section: Introductionmentioning

confidence: 99%

Phase evolution and the mechanism ofJ_cincrease during post-annealing in Ag/(Bi, Pb)2223 tapes

Nakao-Kametani¹,

Osamura²

2005

We have investigated the influence of post-annealing on the current transport and phase/microstructure evolution in Ag/(Bi, Pb)2223 tapes. After post-annealing, the critical current density was about 1.4 times higher. Also the superconducting transition was greatly sharpened and Tc became much higher, even when a magnetic field was applied. The Rietveld analysis suggested that, before post-annealing, a liquid phase remained in the tape, whose mass fraction was estimated as 9.3% from the sum of the phases that formed during post-annealing. Transmission electron microscopy observations revealed that amorphous layers or lattice disorder areas existed at a large number of the (Bi, Pb)2223 grain boundaries. These insulating layers block the superconducting current paths or produce a Josephson-coupled weak link boundary. Upon post-annealing, phase and structure changes took place at the grain boundaries. The insulating amorphous layer converted into metallic 2212 layers. In addition, a faceted structure was formed at the boundary interface such that the tilt boundary became a superconducting through-path. It is strongly suggested that these two factors are critical for increase of the Jc upon post-annealing.

“…As a preceding step of the PIT process, the precursor powder was proven to be of vital importance to the phase formation, microstructure evolution and J c properties. Some parameters related to the precursors, such as calcination temperature [4][5][6][7][8][9][10], particle size distributions [11][12][13][14], lead variations [15,16], and carbon content [17], have been studied to improve the J c performance of Bi-2223/Ag tapes. Among these aspects, the calcination temperature and particle size of the precursor powders are two very sensitive factors for the phase formation and transport J c .…”

Section: Introductionmentioning

confidence: 99%

“…Among these aspects, the calcination temperature and particle size of the precursor powders are two very sensitive factors for the phase formation and transport J c . The reported optimum calcination temperatures varied from 760 • C to 820 • C [5,7,8,10]. The discrepancy may come from the varied starting stoichiometry, fabricating routes and atmosphere as used by different authors.…”

Section: Introductionmentioning

confidence: 99%

Optimization of precursor powders for manufacturing Bi-2223/Ag tapes

Jiang

Yoo

et al. 2002

The phase assemblage and particle sizes of precursor powders have been optimized in a sequence for fabricating Ag/BSCCO-2223 composite tapes. Firstly, an optimal calcination temperature was determined based on the experimental results. Then, the precursors calcined at the optimal temperature were ball-milled for different dwell times to obtain varied particle sizes. The effects of both the phase assemblages and particle sizes of the precursor powder on the phase formation, microstructure and transport J c of Bi-2223/Ag tapes have been investigated. The results show that the precursor phase assemblage has a large impact on the reaction routes, microstructure, and J c property. Meanwhile, a fine powder is beneficial for the grain growth, alignment, and J c enhancement in fully reacted tapes. The best J c was achieved in the tape made from the powder after optimizing the phase assemblage and particle size.