Transmission electron microscopy studies of low-angle grain boundary interactions in melt-textured YBa2Cu3O7−x

Diffusion method has been developed to preferentially dope the grain boundaries of YBa 2 Cu 3 O y bicrystals and polycrystals. Ca and Fe have been used as dopants in this study. The distribution of the dopants is highly localized in the grain boundaries. The critical current density of a YBa 2 Cu 3 O y textured polycrystalline sample is significantly enhanced by doping Ca in grain boundaries; however, it is significantly decreased by doping Fe in grain boundaries. The Ca-doping effect has been explained by charge-carrier compensation in the grain boundaries, which reduces the grain boundary resistance and thus increases the grain boundary critical current. The Fe-doping effect has been explained by worsening the hole loss in grain boundary region, which increases the grain resistance and thus decreases the grain boundary critical current.

Section: Dopant Distribution Around Gbssupporting

confidence: 89%

Chemical preferential doping in grain boundaries of melt textured YBa₂Cu₃O_ysuperconductors

Cheng

Zhu

Zhao

2002

“…They are listed in table 1, along with the concentration and the mean diameter of the second phase, determined through the image analyses. The mean misorientation angles of the subgrains lie between 2.7 and 6.8 degrees, which is consistent with the results of the previous research for similar systems [3][4][5][6]. In the c-GS of YBCO, the misorientation increases in accordance with the growth, although it was not clearly observed by optical microscopy.…”

Section: Resultssupporting

confidence: 91%

“…Thus it is important to control the formation of subgrains for high-field applications along with the enlargement in the grain size of bulk materials. Several models for the subgrain formation have been proposed based on various microstructural observations by polarized optical microscopy and transmission electron microscopy [3][4][5][6]. Two major models for the subgrain formations are: the polygonization of the crystal after solidification through the stress relaxation [3]; and the rearrangement of dislocations created as a result of various instabilities during the solidification [6].…”

Section: Introductionmentioning

confidence: 99%

Subgrain structures in melt-processed REBa₂Cu₃O_y(RE = Y, Sm) bulk superconductors

Ogasawara¹,

Sakai²,

Murakami³

2000

We have studied the subgrain structures in large single-grain REBa 2 Cu 3 O y (RE = Y, Sm) bulk superconductors with polarized optical microscopic observations and pole-figure measurements combined with an x-ray micro-diffraction system. We found that misorientation angles of the subgrains were comparable with those previously obtained on similar melt-processed RE-Ba-Cu-O bulk materials. We will discuss the possible origin for the subgrain formation.

“…An additional factor which is likely to affect the coupling strength across LAGBs is GBD interactions when two or more sets of non-parallel dislocations accommodate the misorientation. As pointed out by Mironova et al [32] (see also Field et al [130] for further discussions) for GBs containing intersecting GBDs, the shape of the strongly coupled channels evolves to almost point-like contacts. Such considerations suggest that weak-link behaviour could be expected even in a low-angle regime for certain arbitrary GBs.…”

Section: Subgrain Boundariesmentioning

confidence: 75%

“…In such cases, the misorientation is accommodated by more than two sets of intersecting grain boundary dislocations (GBDs). Two sets of intersecting GBDs were identified in 4.01 • [0.50 0.86 0.05] [30] and 5.5 • [0.982 0.184 0.026] [24] GBs, and more than two sets have been identified in a 5.163 • [0.6702 −0.2414 0.2398] GB [31] and several GBs reported in [32]. For complex dislocation networks, the GB energy can frequently be lowered by dislocation interactions and reactions which in fact tend to increase the defect density and complexity of the GB microstructure.…”

Section: Characteristics Of Subgrain Boundariesmentioning

confidence: 99%

Tailoring of microstructure and critical currents in directionally solidified

Sandiumenge

Martı́nez

Obradors

1997

Directionally solidified composites display a complex microstructure with several defects coexisting in the matrix and hence the identification of the flux-pinning mechanisms requires a detailed analysis of the critical currents. In this work we review the formation mechanism of twins, stacking faults, microcracks, subgrain boundaries and dislocations in connection with the refining strategies of (211 phase) inclusions and modifications of the microstructure generated through prolonged oxygen annealings and high-temperature plastic deformation of the ceramic. The influence of these defects and post-processing treatments on the critical currents is then analysed focusing on their relative importance as flux-pinning centres at different temperatures and magnetic fields up to 20 T. A complete magnetic phase diagram is finally proposed as a basis for a systematic classification of the observed irreversible superconducting behaviour in single-grain melt-textured composites.