Electromagnetic, atomic structure and chemistry changes induced by Ca-doping of low-angle YBa2Cu3O7–δ grain boundaries

Song, Xueyan; Daniels, G.; Feldmann, D. M.; Gurevich, A.; Larbalestier, D. C.

doi:10.1038/nmat1394

Cited by 82 publications

(80 citation statements)

References 32 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…So far as the possibility of intrinsic granularity is concerned, one important factor is likely to be the low carrier density of ~10 21 cm -3 [4] which is very similar to that found in the cuprates and which produces an intrinsic weak-link behavior at high-angle cuprate grain boundaries [28,29]. However, many additional specific features of the cuprates, including their sensitivity to local oxygen concentration, proximity of the superconducting state to the Mott metal-insulator transition, and cation disorder [30], also play important roles in depressing the superconducting order parameter at grain boundaries. Explicit understanding of the oxypnictides awaits single grain boundary studies that are not yet possible, so for now we restrict our discussion to extrinsic factors that may be playing a role in the behavior of these two Nd and Sm samples, that actually show much better global current flow than the La oxypnictide sample first studied [12].…”

Section: Discussionmentioning

confidence: 99%

Evidence for two distinct scales of current flow in polycrystalline Sm and Nd iron oxypnictides

Yamamoto¹,

Polyanskii²,

Jiang³

et al. 2008

Supercond. Sci. Technol.

128

177

View full text Add to dashboard Cite

Early studies have found quasi-reversible magnetization curves in polycrystalline bulk rare-earth iron oxypnictides that suggest either wide-spread obstacles to intergranular current or very weak vortex pinning. In the present study of polycrystalline samarium and neodymium rare-earth iron oxypnictide samples made by high pressure synthesis, the hysteretic magnetization is significantly enhanced. Magneto optical imaging and study of the field dependence of the remanent magnetization as a function of particle size both show that global currents over the whole sample do exist but that the intergranular and intragranular current densities have distinctively different temperature dependences and differ in magnitude by about 1000. Assuming that the highest current density loops are restricted to circulation only within grains leads to values of ~5×10 6 A/cm 2 at 5 K and self field, while whole-sample current densities, though two orders of magnitude lower are 1000-10000 A/cm 2 , some two orders of magnitude higher than in random polycrystalline cuprates. We cannot yet be certain whether this large difference in global and intragrain current density is intrinsic to the oxypnictides or due to extrinsic barriers to current flow, because the samples contain significant second phase, some of which wets the grain boundaries and produces evidences of SNS proximity effect in the whole sample critical current. 2 Introduction:The recent discovery of superconductivity in the LaFeAsO 1-x F x compound [1] has stimulated a rapid exploration of superconductivity in the rare earth iron oxypnictides [2][3][4][5][6][7][8][9][10][11][12][13][14]. It has now been established that the iron oxypnictides can be superconducting when doped to x ~0.05-0.2 and that they can have transition temperature T c above 40 K when La is replaced by Ce [5] and above 50 K by Pr, Nd, Sm and Gd [7][8][9][10][11]. In a recent paper [12] we addressed the issue of electromagnetic granularity in polycrystalline La iron oxypnictides, finding an asymmetric M(H) loop that indicated an irreversible moment due to hysteretic bulk currents that was almost as small as the reversible magnetization of the superconducting state. In that case we were not able to distinguish definitively between a state where the intragrain pinning was very weak, leading to very low intragrain current densities or to the state where currents were largely confined to the intragrain regions and might have been rather high. Based on the rather high upper critical field B c2 (0) values of 63-65 T observed by Hunte et al.

show abstract

Section: Discussionmentioning

confidence: 99%

Evidence for two distinct scales of current flow in polycrystalline Sm and Nd iron oxypnictides

Yamamoto¹,

Polyanskii²,

Jiang³

et al. 2008

Supercond. Sci. Technol.

128

177

View full text Add to dashboard Cite

show abstract

“…[7][8][9][10] Depression of multiband superconductivity at GBs in pnictides could result from strong interband scattering by imperfect GB structural units in the chain of GB dislocation cores or by strain-or charge-driven Cottrell atmospheres of segregated impurities at the GB. 22,23 Strong antiferromagnetic correlations in the Fe-As planes and GB impurity segregations may also induce local magnetic nanostructures, which would also contribute to the weak link behavior 5 of GBs in pnictides. Given the strong coupling of the superconducting order parameters in different bands, 24 pairbreaking magnetic and nonmagnetic scattering at the GB may play a much greater role in the order parameter suppression at GBs in 122 than in the two-band superconductor MgB 2 in which weak interband coupling and interband impurity scattering are consistent with the lack of weak link behavior of GBs.…”

mentioning

confidence: 99%

Weak-link behavior of grain boundaries in superconducting Ba(Fe1−xCox)2As2 bicrystals

Lee

Jiang

Weiss

et al. 2009

Applied Physics Letters

178

164

View full text Add to dashboard Cite

Abstract:We show that despite the low anisotropy, strong vortex pinning and high irreversibility field H irr close to the upper critical field H c2 of Ba(Fe 1-x Co x ) 2 As 2 , the critical current density J gb across [001] tilt grain boundaries (GBs) of thin film Ba(Fe 1-x Co x ) 2 As 2 bicrystals is strongly depressed, similar to high-T c cuprates. Our results suggest that weak-linked GBs are characteristic of both cuprates and pnictides because of competing orders, low carrier density, and unconventional pairing symmetry. PACS: 74.70.xa, 74.25.F-______________________________________ *

show abstract

“…As described in the introduction, one of the major motivations to study (Yb 1-x Ca x )BCO was to explore the effects of a stronger Ca segregation to GBs predicted by the strain-charge model [7]. This model successfully described the observed non-uniform Ca distribution along and across GBs in Ca-doped YBCO.…”

Section: Gbmentioning

confidence: 99%

“…The strength and orientation of the magnetic field have a significant effect on GB transparency too. A number of studies [5][6][7] found that J c of the GB and the grain converged with increasing field. The field at which J c GB converged with J c grain was found to increase with GB misorientation angle θ. Diaz et al [8] found that J c GB peaks in an angular-dependence study of J c GB , when the magnetic field was aligned with the GB dislocations.…”

Section: Introductionmentioning

confidence: 99%

Study of grain boundary transparency in(Yb1−xCax)B
Li
¹
,
Abraimov
²
,
Polyanskii
³

et al. 2015
Phys. Rev. B
Self Cite
14
0
13
0
View full text Add to dashboard Cite

The residual low angle grain boundary (GB) network is still the most important current-limiting mechanism operating in bi-axially textured rare earth barium copper oxide (REBCO) coated conductors. While Ca-doping is well established to improve supercurrent flow across low angle GBs in weak fields at high temperatures, Ca-doping also depresses T c , making it so far impractical for high exceed J c grain (r GB >1) where the GB pinning is optimized by the field being parallel to the GB dislocations. However, even in this favorable situation, we found that r GB became much smaller at lower temperatures. Calculations of the GB Ca segregation profile predict that the high J c channels between the GB dislocation cores are almost Ca-free. It may be therefore that the positive effects of Ca doping seen by many authors near T c are partly a consequence of the higher T c of these Ca-free channels.

show abstract

Electromagnetic, atomic structure and chemistry changes induced by Ca-doping of low-angle YBa2Cu3O7–δ grain boundaries

Cited by 82 publications

References 32 publications

Evidence for two distinct scales of current flow in polycrystalline Sm and Nd iron oxypnictides

Evidence for two distinct scales of current flow in polycrystalline Sm and Nd iron oxypnictides

Weak-link behavior of grain boundaries in superconducting Ba(Fe1−xCox)2As2 bicrystals

Study of grain boundary transparency in(Yb1−xCax)B
Li
¹
,
Abraimov
²
,
Polyanskii
³

et al. 2015
Phys. Rev. B
Self Cite
14
0
13
0
View full text Add to dashboard Cite

Contact Info

Product

Resources

About

Electromagnetic, atomic structure and chemistry changes induced by Ca-doping of low-angle YBa2Cu3O7–δ grain boundaries

Cited by 82 publications

References 32 publications

Evidence for two distinct scales of current flow in polycrystalline Sm and Nd iron oxypnictides

Evidence for two distinct scales of current flow in polycrystalline Sm and Nd iron oxypnictides

Weak-link behavior of grain boundaries in superconducting Ba(Fe1−xCox)2As2 bicrystals

Study of grain boundary transparency in(Yb1−xCax)BLi1, Abraimov2, Polyanskii3 et al. 2015Phys. Rev. BSelf Cite140130View full textAdd to dashboardCite

Contact Info

Product

Resources

About

Study of grain boundary transparency in(Yb1−xCax)B
Li
¹
,
Abraimov
²
,
Polyanskii
³

et al. 2015
Phys. Rev. B
Self Cite
14
0
13
0
View full text Add to dashboard Cite