A Comparison of Methods for Computing the Residual Resistivity Ratio of High-Purity Niobium

Splett, Jolene D.; Vecchia, Dominic F.; Goodrich, Loren F.

doi:10.6028/jres.116.001

Cited by 11 publications

(5 citation statements)

References 4 publications

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“…It is interesting, however, that the single crystal specimens have lower slopes of resistivity increase with strain, and different rates of recovery, than the fine-grain specimens do. Different resistivity increase with strain was noted in [39], and the slopes in plots (b) and (c) of Fig. 5 are consistent with those earlier data.…”

Section: Single-crystal Resultssupporting

confidence: 91%

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Combined effects of cold work and chemical polishing on the absorption and release of hydrogen from SRF cavities inferred from resistance measurements of cavity-grade niobium bars

Dzyuba¹,

Cooley²

2014

Supercond. Sci. Technol.

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A series of small fine-grained and single-crystal bars, with strain from 0% (recrystallized) to 50%, were given different amounts of chemical polishing. Four-point resistivity () data was used to characterize the electron scattering from dislocations, hydrogen, and any other trace contaminants. As noted by previous studies, annealed Nb displayed a weak linear increase of (11 K) with polishing time due to hydrogen absorption, and bulk hydrogen concentration did not exceed 15% for 200 µm metal removed. Cold-worked samples displayed steeper slopes with polishing time (after subtracting resistivity due to strain alone), suggesting that dislocations assist the absorption of hydrogen during polishing. Absorption accelerated above 30% strain and 100 µm material removal, with room-temperature hydrogen concentration rising rapidly from 2% up to 5%. This threshold is significant, since superconducting radio-frequency (SRF) cavities are usually polished as-formed, with >35% strain, and polishing removes >150 µm of metal. Resistance jumps between 40 and 150 K, which signal the formation of hydride precipitates, were stronger in cold-worked samples, suggesting that dislocations also assist precipitate nucleation. High-vacuum anneals at 800 °C for 2 hours, which are known to fully recrystallize cavity-grade niobium and de-gas hydrogen, removed the 40-150 K jumps and recovered the resistivity increase due to chemical polishing entirely. But, about 30% of the resistivity increase due to cold work remained, possibly due to residual dislocation clusters. Continued annealing only facilitated the diffusion of surface impurities into the bulk and did not recover the initial 0% state. Strain, polishing, and annealing thus appear to combine as irreversible paths that change the material. Bearing this in mind, the significant difference in hydrogen uptake between annealed and coldworked samples suggests that annealing SRF cavities prior to chemical polishing could greatly reduce hydrogen uptake and storage in the metal, reducing risk of quality-factor loss. This inverts key steps of the present widely-used cavity processing sequence.

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Section: Single-crystal Resultssupporting

confidence: 91%

“…Resistance was measured by the same 4 point procedure, and with the same apparatus, that is used for quality control of niobium sheets for SRF programs [37,38] (see also [39]).…”

Section: Resistivity Measurementsmentioning

confidence: 99%

Combined effects of cold work and chemical polishing on the absorption and release of hydrogen from SRF cavities inferred from resistance measurements of cavity-grade niobium bars

Dzyuba¹,

Cooley²

2014

Supercond. Sci. Technol.

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“…at 273 K, and the resistance R 4.2 at the boiling point of He, i.e. at 4.2 K [33]. The RRR measures the contribution of electron scattering at impurities or lattice defects to the total normal state resistance of a superconductor, with high values indicating high-purity materials.…”

Section: Resultsmentioning

confidence: 99%

Electrical transport properties of single-crystal Al nanowires

et al. 2016

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Single-crystal Al nanowires (NWs) were fabricated by thermally induced substitution of vapor-liquid-solid grown Ge NWs by Al. The resistivity of the crystalline Al (c-Al) NWs was determined to be ρ = (131 ± 27) × 10(-9) Ω m, i.e. approximately five times higher than for bulk Al, but they withstand remarkably high current densities of up to 1.78 × 10(12) A m(-2) before they ultimately melt due to Joule heating. The maximum current density before failure correlates with the NW diameter, with thinner NWs tolerating significantly higher current densities due to efficient heat dissipation and the reduced lattice heating in structures smaller than the electron-phonon scattering length. The outstanding current-carrying capacity of the c-Al NWs clearly exceeds those of common conductors and surpasses requirements for metallization of future high-performance devices. The linear temperature coefficient of the resistance of c-Al NWs appeared to be lower than for bulk Al and a transition to a superconducting state in c-Al NWs was observed at a temperature of 1.46 K.

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“…Basically, the more pure material is, the lower residual resistance one can obtain. Since the Residual Resistance Ratio (RRR) is defined as the ratio of a resistance at 300K to a residual resistance (resistance at or just above critical temperature, T c of Nb ∼ 9.2K) [6], one can have high RRR with the more pure material.…”

Section: Introductionmentioning

confidence: 99%

RRR Characteristics for SRF cavities

Jung

Hyun

Joung

2015

Journal of the Korean Physical Society

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The first heavy ion accelerator is being constructed by the rare isotope science project (RISP) launched by the Institute of Basic Science (IBS) in South Korea. Four different types of superconducting cavities were designed, and prototypes were fabricated such as a quarter wave resonator (QWR), a half wave resonator (HWR) and a single spoke resonator (SSR). One of the critical factors determining performances of the superconducting cavities is a residual resistance ratio (RRR).The RRR values essentially represent how much niobium is pure and how fast niobium can transmit heat as well. In general, the RRR degrades during electron beam welding due to the impurity incorporation. Thus it is important to maintain RRR above a certain value at which a niobium cavity shows target performance. In this study, RRR degradation related with electron beam welding conditions, for example, welding power, welding speed, and vacuum level will be discussed.PACS numbers:

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A Comparison of Methods for Computing the Residual Resistivity Ratio of High-Purity Niobium

Cited by 11 publications

References 4 publications

Combined effects of cold work and chemical polishing on the absorption and release of hydrogen from SRF cavities inferred from resistance measurements of cavity-grade niobium bars

Combined effects of cold work and chemical polishing on the absorption and release of hydrogen from SRF cavities inferred from resistance measurements of cavity-grade niobium bars

Electrical transport properties of single-crystal Al nanowires

RRR Characteristics for SRF cavities

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