Diffusion behaviors of hydrogen isotopes in niobium from first-principles

Wei, Lu; An-Yuan, Gao; Liu, YueLin; Dai, Zhenhong

doi:10.1007/s11433-012-4933-0

Cited by 7 publications

(3 citation statements)

References 57 publications

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“…Other input parameters and convergence criteria were kept the same as for the ground state calculations. In the niobium lattice, the activation energy barrier for hydrogen diffusion from one tetrahedral site to the nearest tetrahedral site was found to be 0.18 eV (Figure 4a), which compares well with the reported literature value [47]. However, with the addition of nitrogen, the activation energy barrier along the minimum energy path for hydrogen diffusion in the niobium lattice increased significantly as shown in figure 4b.…”

Section: Effect Of N On H Diffusion In Nbsupporting

confidence: 88%

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

Garg

Balachandran

Adlakha

et al. 2018

Supercond. Sci. Technol.

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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.

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Section: Effect Of N On H Diffusion In Nbsupporting

confidence: 88%

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

Garg

Balachandran

Adlakha

et al. 2018

Supercond. Sci. Technol.

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“…Su coincidencia para los dos tamaños que probamos, 16 y 54 átomos, indica que debe considerarse como el (mejor) valor predicho por nuestra técnica. Observamos además un muy buen acuerdo con valores de otros autores [20] utilizando celdas más grandes y el código VASP [24]. Ambas estimaciones, sin embargo, difieren significativamente de los (abundantes) resultados experimentales [21].…”

Section: Cálculos Ab Initio Preliminaresunclassified

THEORETICAL AND NUMERICAL STUDY OF HYDROGEN DIFFUSION IN Zr-Nb ALLOYS

Beltramo¹,

Ramunni²,

Pasianot³

2022

AnAFA

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Within the framework of the delayed hydride cracking phenomena reported for the pressure tubes of CANDU-type nuclear reactors, we study the influence of the Zr-β(∼20 %Nb -∼80 %Zr) continuous phase on the hydrogen diffusion coefficient,DH, through the Zr-α/ Zr-βbiphasic alloy. We propose an improved phenomenological model forDHwithrespect to those found in the literature. Furthermore, we study the influence of the Nb content on DH for the cubic phase Zr-β, employing the transition state theory furnished with ab-initio parameters provided by the SIESTA code. In particular, 9 ordered alloys are considered with different Nb content and effective activation energies are computed by Arrhenius fits for each alloy. We find that activation energies vary in a non-monotonic way as Nb content increases, reaching a maximum value at about Zr-50 %Nb. Finally, we observe that the predicted and measured larger diffusivity along the tube axis vs. the radial direction, is consistent with the material texture. Moreover, we conclude that the loss of continuity of the Zr-βsheets present in the tube microstructure, is consistent with the decrease of DH in time at agiven temperature.

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“…Tracking of particle diffusion is always considered as a result of the random walk of particles [2,3], and thus the displacements of the particle are handled as isotropic. In recent years, it has become well-recognized that extensive biological, chemical and even physical processes including conformation changes usually occur in nano-, pico-and even femtoseconds [4][5][6][7], and very small spaces [8][9][10][11][12][13][14][15]. For example, the macromolecules in cells are typically separated by only 1-2 nm [5,[16][17][18] and dynamics of these macromolecules occur at the nanoscale.…”

Section: / 16mentioning

confidence: 99%

Asymmetrical free diffusion with orientation-dependence of molecules in finite timescales

Sheng

Guo

et al. 2013

Sci. China Phys. Mech. Astron.

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Using molecular dynamics simulations, we show that free diffusion of a nanoscale particle (molecule) with asymmetric structure critically depends on the orientation in a finite timescale of picoseconds to nanoseconds. In a timescale of ~100 ps, there are ~10% more possibilities for the particle moving along the initial orientation than moving opposite to the orientation; and the diffusion distances of the particle reach ~1 nm. We find that the key to this observation is the orientation-dependence of the damping force to the moving of the nanoscale particle and a finite time is required to regulate the particle orientation. This finding extends the work of Einstein to nano-world beyond random Brownian motion, thus will have a critical role in the understanding of the nanoscale world.

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Diffusion behaviors of hydrogen isotopes in niobium from first-principles

Cited by 7 publications

References 57 publications

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

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

THEORETICAL AND NUMERICAL STUDY OF HYDROGEN DIFFUSION IN Zr-Nb ALLOYS

Asymmetrical free diffusion with orientation-dependence of molecules in finite timescales

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