Physical and Corrosion-electrochemical Properties of the Niobium–Hydrogen System

Khaldeev, G. V.; Gogel, Viktor

doi:10.1070/rc1987v056n07abeh003293

Cited by 12 publications

(10 citation statements)

References 3 publications

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“…This hydrogen can then become trapped inside of the cavity because an oxide layer grows on the niobium upon exposure to water or air, which hinders the transport of hydrogen in or out of the niobium [9]. The enhanced concentration of hydrogen in the near-surface region may be due to trapping of dissolved hydrogen atoms by niobium lattice imperfections -such as vacancies, dislocations, or grain boundaries -other dissolved impurity atoms such as the oxygen provided by the oxide coating, or the interface between the oxide and niobium [19][20][21].…”

Section: Introductionmentioning

confidence: 99%

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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Section: Introductionmentioning

confidence: 99%

Suppression of hydride precipitates in niobium superconducting radio-frequency cavities

Ford

Cooley

Seidman

2013

Supercond. Sci. Technol.

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“…As discussed in a review by Khaldeev and Gogel [2], dissolved hydrogen atoms can become trapped by several mechanisms: (1) the elastic strain that they impart to the niobium lattice upon absorption, known as self-trapping; (2) interaction with other dissolved impurities; and (3) absorption into lattice imperfects -point, line and planar. Trapping enthalpies and their effects on hydrogen diffusion have been evaluated experimentally, and theoretical models have been constructed to include elastic, electronic, and tunneling contributions -a book by Fukai [32] provides detailed information about these topics as well as references to many prior studies.…”

Section: Figurementioning

confidence: 99%

“…Niobium, however, easily absorbs hydrogen if its protective oxide is compromised [1], which can significantly impact its properties. Hydrogen reduces the stability of niobium in corrosive media, either via local charge transfer or via elastic strain [2]. Hydride formation is central to the mechanism of hydrogen embrittlement [3][4][5][6][7][8], which affects the durability of steam piping and reactor membranes.…”

Section: Introductionmentioning

confidence: 99%

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

Ford

Cooley

Seidman

2013

Supercond. Sci. Technol.

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Abstract. Niobium hydride is suspected to be a major contributor to degradation of the quality factor of niobium superconducting radio-frequency (SRF) cavities. In this study, we connect the fundamental properties of hydrogen in niobium to SRF cavity performance and processing. We modeled several of the niobium hydride phases relevant to SRF cavities and present their thermodynamic, electronic, and geometric properties determined from calculations based on density-functional theory. We find that the absorption of hydrogen from the gas phase into niobium is exothermic and hydrogen becomes somewhat anionic. The absorption of hydrogen by niobium lattice vacancies is strongly preferred over absorption into interstitial sites. 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. Small hydride precipitates may then occur near lattice vacancies upon cooling. Vacancy clusters and extended defects should also be enriched in hydrogen, potentially resulting in extended hydride phase regions upon cooling. We also assess the phase changes in the niobium-hydrogen system based on charge transfer between niobium and hydrogen, the strain field associated with interstitial hydrogen, and the geometry of the hydride phases. The results of this study stress the importance of not only the hydrogen content in niobium, but also the recovery state of niobium for the performance of SRF cavities.

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“…Open volume lattice defects (vacancies, vacancy clusters, dislocations), however, are known to have high trapping potential for interstitial impurities, especially hydrogen [6][7][8][9][10][11] , and after the high temperature bake a fraction of several hundreds ppm of hydrogen remains in the lattice 5 in the near surface layer. The formation of so-called "nanohydrides" 10,12 , which are only weakly superconducting by proximity effect 13 below a certain threshold of an applied accelerating field, causes losses above this threshold.…”

mentioning

confidence: 99%

Vacancy-Hydrogen Interaction in Niobium during Low-Temperature Baking

Wenskat

Čı́žek

Liedke

et al. 2020

Sci Rep

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A recently discovered modified low-temperature baking leads to reduced surface losses and an increase of the accelerating gradient of superconducting TESLA shape cavities. We will show that the dynamics of vacancy-hydrogen complexes at low-temperature baking lead to a suppression of lossy nanohydrides at 2 K and thus a significant enhancement of accelerator performance. Utilizing Doppler broadening Positron Annihilation Spectroscopy, Positron Annihilation Lifetime Spectroscopy and instrumented nanoindentation, samples made from European XFEL niobium sheets were investigated. We studied the evolution of vacancies in bulk samples and in the sub-surface region and their interaction with hydrogen at different temperature levels during in-situ and ex-situ annealing.

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Physical and Corrosion-electrochemical Properties of the Niobium–Hydrogen System

Cited by 12 publications

References 3 publications

Suppression of hydride precipitates in niobium superconducting radio-frequency cavities

Suppression of hydride precipitates in niobium superconducting radio-frequency cavities

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

Vacancy-Hydrogen Interaction in Niobium during Low-Temperature Baking

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