Microstructructural comparison of YBa2Cu3O7−x thin films laser deposited in O2 and O2/Ar ambient

Verbist, K.; Kühle, A.; Vasiliev, Alexander L.

doi:10.1016/0921-4534(96)00437-6

Cited by 11 publications

(14 citation statements)

References 30 publications

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“…While the field and temperature dependence of the current density show the qualitative behavior often reported in literature for laser ablated, sputtered, and MO-CVD thin films, the film thickness dependence is consistent only with strong pinning by sparse large second phase inclusions (such as Y 2 O 3 ). A model description of such pinning in different limits of flux line density and film thickness is consistent with the experimentally found behavior, if one assumes the inclu-sions to have the typical size 15 × 15 × 10 nm 3 obtained from previous TEM studies, 22,25 , with a defect density n i ∼ 1 − 3 × 10 21 m −3 . Such a defect density suggests in turn that at high fields, only a fraction of the vortices are pinned; these suffice to hold the entire lattice at rest until the critical current density is reached.…”

Section: Discussionsupporting

confidence: 78%

“…22,23 Other authors have reported the presence of Y 2 O 3 inclusions in laser-ablated films as well, with typical densities n i Ϸ10 22 m Ϫ3 for inclusions of diameter D i ϳ3 -5 nm and n i Ϸ10 21 m Ϫ3 for D i ϳ10-20 nm. 24,25 Pinning by such large defects turns out to be conveniently described using an extension of the theory of strong pinning of Ovchinnikov and Ivlev, 26 which we shall develop below ͑Sec. II͒.…”

Section: ͑5͒mentioning

confidence: 99%

“…22,23 Other authors have reported the presence of Y 2 O 3 inclusions in laser-ablated films as well, with typical densities n i ≈ 10 22 m −3 for inclusions of diameter D i ∼ 3 -5 nm, and n i ≈ 10 21 m −3 for D i ∼ 10 -20 nm. 24,25 Pinning by such large defects turns out to be conveniently described using an extension of the theory of strong pinning of Ovchinnikov and Ivlev 26 , which we shall develop below (II). Our model is, to our knowledge, the only that consistently describes both the field-and thickness dependence of the critical current density in YBa 2 Cu 3 O 7−δ films.…”

Section: Introductionmentioning

confidence: 99%

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Strong pinning in high-temperature superconducting films

et al. 2002

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Detailed measurements of the critical current density j c of YBa 2 Cu 3 O 7Ϫ␦ films grown by pulsed laser deposition reveal the increase of j c as a function of film thickness. Both this thickness dependence and the field dependence of the critical current are consistently described using a generalization of the theory of strong pinning of Ovchinnikov and Ivlev ͓Phys. Rev. B 43, 8024 ͑1991͔͒. From the model, we deduce values of the defect density (10 21 m Ϫ3 ) and the elementary pinning force, which are in good agreement with the generally accepted values for Y 2 O 3 inclusions. In the absence of clear evidence that the critical current is determined by linear defects or modulations of the film thickness, our model provides an alternative explanation for the rather universal field dependence of the critical current density found in YBa 2 Cu 3 O 7Ϫ␦ films deposited by different methods.

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Section: Discussionsupporting

confidence: 78%

Section: ͑5͒mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Strong pinning in high-temperature superconducting films

et al. 2002

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“…This means that atomic size point defects such as oxygen vacancies are unlikely the dominant pinning centers, and r p should be comparable to the dimension of other defects, such as precipitates and secondary-phase inclusions which are on the order of few to tens of nanometers in dimension. [10][11][12] Assuming that pinning in YBCO films is dominated by these large point defects, L c would be up to tens of nanometers, still an order of magnitude smaller than the relevant film thickness at which J c -t is important. It should be mentioned that the measured irreversible field H irr of YBCO thin films 13 has suggested an L c on the order of submicrometer.…”

mentioning

confidence: 99%

Effect of temperature and magnetic field on the thickness dependence of the critical current density ofYBa2Cu3O7−x
Wang
¹
,
Wu
²

2007
Phys. Rev. B
24
1
4
0
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In order to shed light on the puzzling thickness ͑t͒ dependence of the critical current density ͑J c ͒ in YBa 2 Cu 3 O 7−x ͑YBCO͒ films at 77 K and self-field, we have investigated J c -t behavior as a function of temperature ͑T͒ and applied magnetic field ͑H͒ in the thickness range that is within the modified Larkin length L c . It has been found that the J c -t behavior can be well described by the collective pinning ͑CP͒ model as monotonically decreasing J c ϳ t −1/2 when thermal assisted flux motion ͑TAFM͒ is suppressed at low T close to zero. TAFM becomes increasingly important at elevated temperatures and causes deviation of the J c -t from the CP model in the thickness range below the magnetic penetration depth. The deviation is more pronounced at smaller thickness and increases with T and H. Consequently, a completely reversed J c -t from monotonically decreasing to monotonically increasing occurs when TAFM dominates in high T and H ranges. This result suggests that the monotonic decreasing J c -t behavior is an intrinsic property of uniform YBCO films, while extrinsic effects such as material nonuniformity can greatly complicate it.The strong dependence of critical current density ͑J c ͒ on the thickness ͑t͒ of high-T c superconducting ͑HTS͒ films has presented a tough question that challenges our understanding of basic physics governing electric transport properties in HTS films. 1-5 Basically, J c measured at 77 K and self-field ͑SF͒ on films of HTS materials, such as YBa 2 Cu 3 O 7−x ͑YBCO͒, decreases monotonically with increasing film thickness. A basic question is whether this J c -t behavior is simply caused by material inhomogeneity through thickness or related to an intrinsic property of superconductors. It should be realized that the major J c reduction occurs in the thickness range below ϳ0.6 m, where microstructure degradation is not a major concern. Interestingly, the J c data reported on a large number of YBCO film samples 5-7 made with different techniques fall more or less on the curve of J c ϳ t −1/2 at 77 K and SF, which agrees with the prediction of weak collective pinning model ͑CP͒ for superconducting films thinner than the longitudinal collective pinning length L c ͑Larkin length͒. 8 In the CP model, a quantized magnetic flux line ͑FL͒ with a length of L Ͻ L c is rigid and cannot bend to accommodate different pinning centers nearby. When the dominant pinning centers are randomly distributed point defects, the pinning force ͑F p ͒ exerted on a FL scales as L 1/2 while the Lorentz force scales as L. This leads to the J c ϳ t −1/2 behavior. As L exceeds L c , the FL resumes its elasticity and bends itself to accommodate the pinning center, resulting in a thickness-independent J c .Although the CP model fits the SF J c -t relatively well at 77 K, some questions remain. The first question is about the order of magnitude of the L c . The original L c for a weak collective pinning system is calculated from L c Ϸ r p ͑J 0 / J c ͒ 1/2 , where r p is the pinning center interaction radius and J...

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“…Many publications proved the existence of island nuclei even for monolayer c-axis YBCO films, and the islands grew larger with the film thickness. 20,21 The chemical compositions of precipitates have been reported as Y-rich or Cu-rich phases, 6,7,10,22 while a similar composition as the YBCO film matrix has been frequently observed for island-shaped precipitates. Growth modes reported for c-axis YBCO films were the island growth mode, [13][14][15] spiral growth mode, [16][17][18] or layer-by-layer growth mode 19 above a certain film thickness, while the layer-by-layer growth mode did not occur for the initial growth stage of YBCO.…”

Section: Introductionmentioning

confidence: 93%

Growth mechanism of YBa₂Cu₃O_7–δthin films and precipitates on planar and vicinal SrTiO₃substrates

et al. 2000

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Effects of the vicinal angle, film thickness, and temperature on the growth modes, microstructures, and electrical properties of YBa 2 Cu 3 O 7−␦ on SrTiO 3 were studied. Island growth transition between the initial nucleation and the later coalescence stages was observed with film thickness on a planar SrTiO 3 , while no islands were observed at the later stage due to the step-flow mode. As the growth temperature increased, a-axis precipitates were transformed to c-axis precipitates (islands), while no islands formed on vicinal SrTiO 3 . The supercurrent critical temperature was strongly related to the substrate vicinal angle due to the step-flow mode.

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Microstructructural comparison of YBa2Cu3O7−x thin films laser deposited in O2 and O2/Ar ambient

Cited by 11 publications

References 30 publications

Strong pinning in high-temperature superconducting films

Strong pinning in high-temperature superconducting films

Effect of temperature and magnetic field on the thickness dependence of the critical current density ofYBa2Cu3O7−x
Wang
¹
,
Wu
²

2007
Phys. Rev. B
24
1
4
0
View full text Add to dashboard Cite

Growth mechanism of YBa₂Cu₃O_7–δthin films and precipitates on planar and vicinal SrTiO₃substrates

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Microstructructural comparison of YBa2Cu3O7−x thin films laser deposited in O2 and O2/Ar ambient

Cited by 11 publications

References 30 publications

Strong pinning in high-temperature superconducting films

Strong pinning in high-temperature superconducting films

Effect of temperature and magnetic field on the thickness dependence of the critical current density ofYBa2Cu3O7−xWang1, Wu2 2007Phys. Rev. B24140View full textAdd to dashboardCite

Growth mechanism of YBa2Cu3O7–δthin films and precipitates on planar and vicinal SrTiO3substrates

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Effect of temperature and magnetic field on the thickness dependence of the critical current density ofYBa2Cu3O7−x
Wang
¹
,
Wu
²

2007
Phys. Rev. B
24
1
4
0
View full text Add to dashboard Cite

Growth mechanism of YBa₂Cu₃O_7–δthin films and precipitates on planar and vicinal SrTiO₃substrates