Uranium chemistry and pinning centers in high temperature superconductor

Sawh, Ravi‐Persad; Ren, Yanru; Weinstein, R.; Hennig, Wolfgang; Nemoto, Takayuki

doi:10.1016/s0921-4534(98)00345-1

Cited by 30 publications

(31 citation statements)

References 8 publications

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“…In this method, non-superconducting deposits embedded in the crystal matrix can act as pinning centers. The non-superconducting deposits can be composed of elements foreign to the HTS [3], [4]. When nonnative elements are admixed into the HTS powders and textured, one resulting possibility is that the foreign elements interact with other native elements in the HTS to form precipitates.…”

Section: Introductionmentioning

confidence: 99%

Sub-Micron Non-Superconducting Deposits That Fail to Act as Pinning Centers in Textured YBCO Superconductor

Sawh

Weinstein

Parks

et al. 2007

IEEE Trans. Appl. Supercond.

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A conundrum is observed where one type of small, non-superconducting particles fails to provide pinning, in textured YBCO superconductor, while other non-superconducting particles of comparable size and number density, pin very well. Pinning centers in high temperature superconductors (HTS) have been shown to greatly enhance critical current density ( ). An experiment was performed in which large grain YBCO doped with uranium (U), but no platinum (Pt), was produced. Profuse deposits of a U-Y-Ba-O compound were formed during texturing. These U-rich deposits have an almost spherical morphology with an average diameter of 300 nm and are uniformly distributed inside the YBCO. Conventional wisdom dictates that the U-Y-Ba-O sub-micron deposits should act as pinning centers and increase . However, in tests of via trapped magnetic flux density at 77 K, no increase was measured. This result is especially surprising because chemically similar and morphologically indistinguishable deposits of U-Pt-Y-Ba-O, found in (U + Pt)-doped YBCO, increasedby a factor exceeding 2. The deposits compared had the same size and number density. Neither deposits significantly affected critical temperature ( ). One difference between these two compounds is that the non-pinning U-Y-Ba-O deposits have a single perovskite structure, while the U-Pt-Y-Ba-O pinning centers are a double perovskite. Data are presented on the remarkably similar morphology and strikingly different ability to trap magnetic flux density of the U-Y-Ba-O and U-Pt-Y-Ba-O deposits.Index Terms-Ineffective pinning centers, second phase deposits, single perovskite, sub-micron sized precipitates.

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Section: Introductionmentioning

confidence: 99%

Sub-Micron Non-Superconducting Deposits That Fail to Act as Pinning Centers in Textured YBCO Superconductor

Sawh

Weinstein

Parks

et al. 2007

IEEE Trans. Appl. Supercond.

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“…T C is defined as the midpoint of the temperature transition. In all samples measured, the T C is determined to be between 90 K and 91 K. The estimated error in our T C measurement is ± 0.5 K. With the samples being large, the value obtained for T C is rather typical for bulk YBCO superconductors [8][9]. The T C transition of all samples appears to be sharp.…”

Section: Critical Temperature (T C )mentioning

confidence: 56%

“…This is easily seen in FIGURE 3 where all the elements increase in atomic % with increasing size, or increasing W atomic % except Cu, which instead decreases. It is widely observed in melt-textured YBCO superconductor that large deposits (up to several hundred micrometers in size) of a compound rich in Ba and Cu is a byproduct of the texturing process, e.g., [1][2][3][4][5][6][8][9]. A similar analysis (not shown) of the (W +Pt)-doped samples also concluded that Cu is not a component of the W-Pt-Y-Ba-O particles.…”

Section: Microstructurementioning

confidence: 67%

“…Just like the W-Y-Ba-O deposits, B TRAP measurements indicate that the U-rich deposits, identified as (U 0.4 Y 0.6 )BaO 3 (U-Y-Ba-O), are also ineffective pinning centers, and do not increase the self-field J C of samples. These results were compared to (U + Pt)-doped samples that contained profuse sub-micrometer deposits of a (U 0.6 Pt 0.4 )YBa 2 O 3 (U-Pt-Y-Ba-O) compound [9]. The U-Pt-Y-Ba-O deposits are effective pinning centers and increase B TRAP in the same manner as the W-Pt-Y-Ba-O deposits, i.e., we observed a monotonic increase in B TRAP as U doping levels were increased.…”

Section: An Earlier Experiments With Uranium-doped Pt-free Samplesmentioning

confidence: 99%

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The Puzzle of Two Different Sub-Micrometer Tungsten-Rich Deposits in Bulk Ybco: One Acts as Pinning Centers and the Other Does Not

Sawh¹,

Weinstein²,

Parks³

et al. 2010

AIP Conference Proceedings

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Two types of large grain YBCO samples doped with tungsten oxide, one with platinum and the other without, were produced using a slow cooling process. Observations of the trapped magnetic flux density showed that the flux density of the W-doped, Pt-free samples did not change with W doping levels of up to 2.1 mol%. In contrast, the (W + Pt)-doped samples resulted in a monotonic improvement in trapped magnetic flux density as a function of W doping. Microstructure studies indicate that both types of samples contain profuse sub-micrometer deposits of a W-rich compound. The Pt-free samples contain (W 0.4 Y 0.6 )BaO 3 deposits while the (W + Pt)-doped samples contain deposits of a (W 0.5 Pt 0.5 )YBa 2 O 6 compound. Both types of deposits are of essentially the same size and have comparable number density. The results are strikingly similar to an earlier experiment in which uranium doped, Pt-free, large grain YBCO also did not show any improvement in trapped magnetic flux density. The U-doped, Pt-free samples contain profuse sub-micrometer deposits of a (U 0.4 Y 0.6 )BaO 3 compound, which have been shown to be ferromagnetic. The inability of both the (W 0.4 Y 0.6 )BaO 3 and (U 0.4 Y 0.6 )BaO 3 submicrometer deposits to act as pinning centers in self-field, suggest that this behavior is systematic.

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“…It has been reported that a small amount of uranium oxide leads to a formation of YBa 2 (U,Pt)O 6 [29]. Later, Hari Babu et al have found a new compound, Y 2 Ba 4 CuUO y [30].…”

Section: -2 New Type Of Pinning Centersmentioning

confidence: 99%

Nanocomposite RE-Ba-Cu-O Bulk Superconductors

Iida

2015

Oxide Thin Films, Multilayers, and Nanocomposites

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Nanocomposite oxide high-temperature bulk superconductors can be used as "quasi-magnets". Thanks to the recent progress of material processing, "quasi-magnet" with 26 mm diameter can generate a large field of 17.6 T at 26 K. These results are highly attractive for applications, involving levitation of permanent magnets on the bulk superconductors. Indeed, several other applications such as motors and magnetic resonance microscope using bulk superconductors have been proposed and demonstrated. In this chapter, we describe several techniques to improve the magnetic properties for bulk superconductors together with some basics such as phase diagrams and solidifications.

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Uranium chemistry and pinning centers in high temperature superconductor

Cited by 30 publications

References 8 publications

Sub-Micron Non-Superconducting Deposits That Fail to Act as Pinning Centers in Textured YBCO Superconductor

Sub-Micron Non-Superconducting Deposits That Fail to Act as Pinning Centers in Textured YBCO Superconductor

The Puzzle of Two Different Sub-Micrometer Tungsten-Rich Deposits in Bulk Ybco: One Acts as Pinning Centers and the Other Does Not

Nanocomposite RE-Ba-Cu-O Bulk Superconductors

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