First-principles calculations of niobium hydride formation in superconducting radio-frequency cavities

Ford, Denise C.; Cooley, L. D.; Seidman, David N.

doi:10.1088/0953-2048/26/9/095002

Cited by 24 publications

(27 citation statements)

References 83 publications

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“…First-principle calculations of Nb hydride formation showed that a single vacancy can accommodate six hydrogen atoms in the symmetrically equivalent lowest-energy sites and additional hydrogen in the nearby interstitial sites affected by the strain field. This indicates that a vacancy can serve as a nucleation center for hydride phase formation [19]. The trapping in vacancies was experimentally confirmed by positron annihilation experiments [28] where four hydrogen atoms were detected in one vacancy.…”

Section: Introduction: Hydrogen Absorption In Metals-bulk Versus Thinmentioning

confidence: 85%

“…An example is Nb-based superconducting radio-frequency cavities of particle accelerators, where metal-hydride surface layers can develop, leading to undesirable extra surface resistivity [19]. For a theoretical understanding of the remarkable changes of thin-film properties due to hydrogen charging, it is important to know how hydrogen is incorporated into the films, whether thermodynamic phase diagrams of the corresponding bulk materials are applicable, and how hydrogen absorption and its kinetics depend on various external parameters such as temperature and hydrogen pressure.…”

Section: Introduction: Hydrogen Absorption In Metals-bulk Versus Thinmentioning

confidence: 99%

“…The trapping in vacancies was experimentally confirmed by positron annihilation experiments [28] where four hydrogen atoms were detected in one vacancy. The issue of hydrogen absorption and trapping in thin films (<100 nm) due to strain field effects is extensively discussed in the literature, see references 17-25 in [19], and in [29].…”

Section: Introduction: Hydrogen Absorption In Metals-bulk Versus Thinmentioning

confidence: 99%

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Hydrogen Absorption in Metal Thin Films and Heterostructures Investigated in Situ with Neutron and X-ray Scattering

Callori

Rehm

Causer

et al. 2016

Metals

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Due to hydrogen possessing a relatively large neutron scattering length, hydrogen absorption and desorption behaviors in metal thin films can straightforwardly be investigated by neutron reflectometry. However, to further elucidate the chemical structure of the hydrogen absorbing materials, complementary techniques such as high resolution X-ray reflectometry and diffraction remain important too. Examples of work on such systems include Nb-and Pd-based multilayers, where Nb and Pd both have strong affinity to hydrogen. W/Nb and Fe/Nb multilayers were measured in situ with unpolarized and polarized neutron reflectometry under hydrogen gas charging conditions. The gas-pressure/hydrogen-concentration dependence, the hydrogen-induced macroscopic film swelling as well as the increase in crystal lattice plane distances of the films were determined. Ferromagnetic-Co/Pd multilayers were studied with polarized neutron reflectometry and in situ ferromagnetic resonance measurements to understand the effect of hydrogen absorption on the magnetic properties of the system. This electronic effect enables a novel approach for hydrogen sensing using a magnetic readout scheme.

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Section: Introduction: Hydrogen Absorption In Metals-bulk Versus Thinmentioning

confidence: 85%

Section: Introduction: Hydrogen Absorption In Metals-bulk Versus Thinmentioning

confidence: 99%

Section: Introduction: Hydrogen Absorption In Metals-bulk Versus Thinmentioning

confidence: 99%

See 1 more Smart Citation

Hydrogen Absorption in Metal Thin Films and Heterostructures Investigated in Situ with Neutron and X-ray Scattering

Callori

Rehm

Causer

et al. 2016

Metals

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“…Consequently, the underlying mechanisms for this effect are also not well understood, although a number of models have been proposed [17]. Recent studies suggest connections to the oxygen and hydrogen concentrations, and niobium vacancies, which we have shown to nucleate hydride precipitates in a recent density functional theory study [23]. However, a single model that explains all these effects does not exist.…”

Section: Introductionmentioning

confidence: 91%

Suppression of hydride precipitates in niobium superconducting radio-frequency cavities

Ford

Cooley

Seidman

2013

Supercond. Sci. Technol.

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Niobium hydride is a suspected contributor to degraded niobium superconducting radio-frequency (SRF) cavity performance by Q slope and Q disease. The concentration and distribution of hydrogen atoms in niobium can be strongly affected by the cavity processing treatments. This study provides guidance for cavity processing based on density functional theory calculations of the properties of common processing impurity species-hydrogen, oxygen, nitrogen, and carbon-in the body-centered cubic (bcc) niobium lattice. We demonstrate that some fundamental properties are shared between the impurity atoms, such as anionic character in niobium. The strain field produced, however, by hydrogen atoms is both geometrically different and substantially weaker than the strain field produced by the other impurities. We focus on the interaction between oxygen and hydrogen atoms in the lattice, and demonstrate that the elastic interactions between these species and the bcc niobium lattice cause trapping of hydrogen and oxygen atoms by bcc niobium lattice vacancies. We also show that the attraction of oxygen to a lattice vacancy is substantially stronger than the attraction of hydrogen to the vacancy. Additionally hydrogen dissolved in niobium tetrahedral interstitial sites can be trapped by oxygen, nitrogen, and possibly carbon atoms dissolved in octahedral interstitial sites. These results indicate that the concentration of oxygen in the bcc lattice can have a strong impact on the ability of hydrogen to form detrimental phases. Based on our results and a literature survey, we propose a mechanism for the success of the low-temperature annealing step applied to niobium SRF cavities. We also recommend further examination of nitrogen and carbon in bcc niobium, and particularly the role that nitrogen can play in preventing detrimental hydride phase formation.

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“…Note that some of the hydrogen can also be trapped by vacancies. Two situations may occur: in a single vacancy up to six H atoms can be trapped, and there are evidences that more H tends to gather in the vicinity, providing nucleation sites for hydrides [121]. In the presence of interstitials atoms like O, N, C, those atoms will occupy preferentially the vacancy: each oxygen, nitrogen or carbon impurity traps only a single hydrogen atom under formation of oxygen-hydrogen, nitrogen-hydrogen or carbon-hydrogen pairs, where the trapped hydrogen occupies interstitial trap sites in the neighborhood of the trapping impurity [122][123][124][125].…”

Section: A Segregation Due To Crystalline Defectsmentioning

confidence: 99%

Influence of crystalline structure on rf dissipation in superconducting niobium

Antoine

2019

Phys. Rev. Accel. Beams

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Bulk niobium is the most common material used in the fabrication of rf superconducting cavities for accelerators. Predicting and reducing the rf surface dissipation in these cavity structures is mandatory, since it has a tremendous cost impact on the large accelerator projects. In this paper the author hopes to demonstrate that sources of dissipation usually attributed to external causes (mainly flux trapping during cooldown and hydrides precipitates) are related to the same type of crystalline defects that affect the local superconducting properties and can be at the source of early vortex penetration at the surface. We also want to show how these types of defects can explain some of the discrepancies observed from other laboratories in niobium cavity doping experiments. Understanding the origin and the role of these defects could provide direction for improving material specifications as well as improving fabrication control from sheet material to completed cavity. In particular, we will demonstrate that dislocation entanglements, due to the fabrication damage layer, have the strongest impact for the pinning behavior of trapped flux, as well as hydrogen segregation in cavity niobium. The author wishes to present to the superconducting radio frequency (SRF) accelerator community the synthesis of experimental results scattered in the literature, completed with some personal results. The results of this effort provide a new perspective on recently published work in the domain of SRF cavity doping and sensitivity to trapped flux during cooldown. I will also try to draw whenever possible, some conclusions about other types of superconductors used for SRF applications including Nb=Cu thin films and to discuss their possible change of behavior with field or frequency. I will concentrate on surface and material science aspects since the experimental results on rf cavities have already been treated elsewhere.

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First-principles calculations of niobium hydride formation in superconducting radio-frequency cavities

Cited by 24 publications

References 83 publications

Hydrogen Absorption in Metal Thin Films and Heterostructures Investigated in Situ with Neutron and X-ray Scattering

Hydrogen Absorption in Metal Thin Films and Heterostructures Investigated in Situ with Neutron and X-ray Scattering

Suppression of hydride precipitates in niobium superconducting radio-frequency cavities

Influence of crystalline structure on rf dissipation in superconducting niobium

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