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Title: Revealing the role of nitrogen on hydride nucleation and stability in pure niobium using first-principles calculations

Abstract

Niobium provides the basis for all superconducting radio frequency (SRF) cavities in use, however, hydrogen is readily absorbed by niobium during cavity fabrication and subsequent niobium hydride precipitation when cooled to cryogenic temperatures degrades its superconducting properties. In the last few years the addition of dopant elements such as nitrogen has been experimentally shown to significantly improve the quality factor of niobium SRF cavities. One of the contributors to Q degradation can be presence of hydrides; however, the underlying mechanisms associated with the kinetics of hydrogen and the thermodynamic stability of hydride precipitates in the presence of dopants are not well known. Using first principles calculations, the effects of nitrogen on the energetic preference for hydrogen to occupy interstitial sites and hydride stability are examined. In particular, the presence of nitrogen significantly increased the energy barrier for hydrogen diffusion from one tetrahedral site to another interstitial site. Furthermore, the beta niobium hydride precipitate became energetically unstable upon addition of nitrogen in the niobium matrix. Through electronic density of states and valence charge transfer calculations, nitrogen showed a strong tendency to accumulate charge around itself, thereby decreasing the strength of covalent bonds between niobium and hydrogen atoms leading to a verymore » unstable state for hydrogen and hydrides. These calculations show that the presence of nitrogen during processing plays a critical role in controlling hydride precipitation and subsequent SRF properties.« less

Authors:
 [1]; ORCiD logo [2]; ORCiD logo [3]; ORCiD logo [4];  [5]; ORCiD logo [1]
  1. Arizona State Univ., Tempe, AZ (United States). School for Engineering of Matter, Transport, and Energy
  2. Florida State Univ., Tallahassee, FL (United States). National High Magnetic Field Lab. (MagLab), Applied Superconductivity Center
  3. Arizona State Univ., Tempe, AZ (United States). School for Engineering of Matter, Transport, and Energy; Indian Inst. of Technology-Madras, Chennai (India). Dept. of Applied Mechanics
  4. Florida State Univ., Tallahassee, FL (United States). National High Magnetic Field Lab. (MagLab), Applied Superconductivity Cente
  5. Michigan State Univ., East Lansing, MI (United States). Dept. of Material Sciences and Engineering
Publication Date:
Research Org.:
Arizona State Univ., Tempe, AZ (United States)
Sponsoring Org.:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
OSTI Identifier:
1501466
Grant/Contract Number:  
SC0009962
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Superconductor Science and Technology
Additional Journal Information:
Journal Volume: 31; Journal Issue: 11; Journal ID: ISSN 0953-2048
Publisher:
IOP Publishing
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Niobium; Superconductivity; Hydride; Nitrogen

Citation Formats

Garg, P., Balachandran, S., Adlakha, I., Lee, P. J., Bieler, T. R., and Solanki, K. N.. Revealing the role of nitrogen on hydride nucleation and stability in pure niobium using first-principles calculations. United States: N. p., 2018. Web. doi:10.1088/1361-6668/aae147.
Garg, P., Balachandran, S., Adlakha, I., Lee, P. J., Bieler, T. R., & Solanki, K. N.. Revealing the role of nitrogen on hydride nucleation and stability in pure niobium using first-principles calculations. United States. doi:10.1088/1361-6668/aae147.
Garg, P., Balachandran, S., Adlakha, I., Lee, P. J., Bieler, T. R., and Solanki, K. N.. Fri . "Revealing the role of nitrogen on hydride nucleation and stability in pure niobium using first-principles calculations". United States. doi:10.1088/1361-6668/aae147.
@article{osti_1501466,
title = {Revealing the role of nitrogen on hydride nucleation and stability in pure niobium using first-principles calculations},
author = {Garg, P. and Balachandran, S. and Adlakha, I. and Lee, P. J. and Bieler, T. R. and Solanki, K. N.},
abstractNote = {Niobium provides the basis for all superconducting radio frequency (SRF) cavities in use, however, hydrogen is readily absorbed by niobium during cavity fabrication and subsequent niobium hydride precipitation when cooled to cryogenic temperatures degrades its superconducting properties. In the last few years the addition of dopant elements such as nitrogen has been experimentally shown to significantly improve the quality factor of niobium SRF cavities. One of the contributors to Q degradation can be presence of hydrides; however, the underlying mechanisms associated with the kinetics of hydrogen and the thermodynamic stability of hydride precipitates in the presence of dopants are not well known. Using first principles calculations, the effects of nitrogen on the energetic preference for hydrogen to occupy interstitial sites and hydride stability are examined. In particular, the presence of nitrogen significantly increased the energy barrier for hydrogen diffusion from one tetrahedral site to another interstitial site. Furthermore, the beta niobium hydride precipitate became energetically unstable upon addition of nitrogen in the niobium matrix. Through electronic density of states and valence charge transfer calculations, nitrogen showed a strong tendency to accumulate charge around itself, thereby decreasing the strength of covalent bonds between niobium and hydrogen atoms leading to a very unstable state for hydrogen and hydrides. These calculations show that the presence of nitrogen during processing plays a critical role in controlling hydride precipitation and subsequent SRF properties.},
doi = {10.1088/1361-6668/aae147},
journal = {Superconductor Science and Technology},
issn = {0953-2048},
number = 11,
volume = 31,
place = {United States},
year = {2018},
month = {10}
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on October 12, 2019
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