Garg, P. Adlakha, I. Balachandran, S. Bieler, T.R. Lee, P.J. Solanki, K.N. JACoW Geneva, Switzerland 978-3-95450-191-5 10.18429/JACoW-SRF2017-THPB002 English 741-745 THPB002 ion niobium site cavity electron Contribution to a conference proceedings 2018 2018-01 https://doi.org/10.18429/JACoW-SRF2017-THPB002 http://jacow.org/srf2017/papers/thpb002.pdf It is known that formation and growth of Nb hydride degrades superconducting radio frequency (SRF) properties of Nb cavities and the treatments that reduce H concentration improve quality factor. Recently it is has also been shown that addition of N through doping or infusion improves the quality factor. Thus, we probe role of N addition in Nb on hydride precipitation and stability through first principles calculations & compared with coupon samples. In presence of N, energetic preference for H to occupy interstitial sites in the vicinity of N is reduced. Furthermore, presence of N forces H to occupy interstitial octahedral site instead of a tetrahedral site. The thermodynamic stability of hydride is decreased in the presence of N in Nb.The quantum insights using charge transfer and density of states show a strong tendency of N to accumulate charge, thereby decreasing the bond strength of neighboring Nb and H atoms. These atomic scale results explain the lesser tendency of surface hydride formation in SRF Nb cavities in presence of N. These results are consistent with metallographic examination of N-treated Nb coupons, which show suppressed hydride formation near N-treated surface.