Equilibrium positions of hydrogen atoms in the crystal lattice of metals

The position of interstitial atoms of hydrogen in the lattice of a metal solvent is considered. The probability of their positions is estimated under the assumption that they behave like linear uncoupled oscillators. Calculations are made using experimental data on the solubility of hydrogen and deuterium in metals with bcc and fcc structure.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 30–32, October, 1980.     

Lattice location and trapping of hydrogen implanted in FCC metals

Hydrogen implantation in fcc metals is studied by ion-beam analysis methods. The lattice location and long-range migration are carried out after low-temperature implantation defects is found.     

Tendency to nearly cubic local lattice structure around interstitial hydrogen in the alkali metals

The behaviour of the lattice response in the bcc alkali metals and the change in sign of the impurity-host interaction between first and second neighbour distances are shown to cooperate to build up a relaxed atomic environment which, for the D_4h ‘octahedral’ interstitial position, is close to a regular octahedral coordination. The calculation is done by using the self-consistent electron density for a proton in jellium to take into account non-linear screening, and the relaxed crystal structure is found by the method of lattice statics. The displacements around the hydrogen impurity are found to be many time larger than those predicted earlier by use of the spherical solid model.     

Electromigration in a hydrogen lattice fluid

We extend the thermodynamic theory of hydrogen in metals to include the effect of internal coherence strains on the electromigration of interstitially dissolved protons. We study, in particular, the long-time behavior of local density relaxation near a critical point of the hydrogen lattice fluid. The contingency of damped oscillatory relaxation is discussed.Dedicated to Professor W. Brenig on the occasion of his 60th birthday     

A TDPAC study of the lattice location of implanted indium in silicon

Abstract

The annealing behaviour of indium implanted silicon (doses 10¹¹?10¹³ atoms/cm²) was studied by time differential perturbed angular correlation spectroscopy. Besides the substitutional site two types of defect configurations were observed. In the as-implanted condition the substitutional In fraction remains below 20% even at the lowest dose. This result is in accordance with the prediction of the track amorphization model.     

The nuclear Yukawa model on a lattice

We present the results of the quantum field theory approach to the nuclear Yukawa model obtained by standard lattice techniques. We have considered the simplest case of two identical fermions interacting via a scalar meson exchange. Calculations have been performed using Wilson fermions in the quenched approximation. We found the existence of a critical coupling constant above which the model cannot be numerically solved. The range of the accessible coupling constants is below the threshold value for producing two-body bound states. Two-body scattering lengths have been obtained and compared to the non-relativistic results.     

Time-resolved DNP study on the hydrogen abstraction reaction of benzaldehyde

The kinetic feature of intermediate free radical in the photochemical reaction of benzaldehyde is studied by time-resolved DNP technique. The feature of nuclear polarization is different between laser excitation and continuous light excitation. This difference is explained by the difference of the lifetime of intermediate free radicals caused by the difference of the concentration of intermediate free radicals. The time-resolved DNP shows that the lifetime of intermediate free radical is about 300 ns and the cross-relaxation process of aromatic proton of ketyl radical is shorter than 300 ns.     

Quantum nuclear effects on the location of hydrogen above and below the palladium (100) surface

We report ab initio path integral molecular dynamics simulations of hydrogen and deuterium adsorbed on and absorbed in the Pd(100) surface at 100 K. Significant quantum nuclear effects are found by comparing with conventional ab initio molecular dynamics simulations with classical nuclei. For on-surface adsorption, hydrogen resides higher above the surface when quantum nuclear effects are included, an effect which brings the computed height into better agreement with experimental measurements. For sub-surface absorption, the classical and quantum simulations differ in an even more significant manner: the classically stable subsurface tetrahedral position is unstable when quantum nuclear effects are accounted for. This study provides insight that aids in the interpretation of experimental results and, more generally, underscores that despite the computational cost ab initio path integral molecular dynamics simulations of surface and subsurface adsorption are now feasible.     

The effect of lattice constant on the storage capacity of hydrogen hydrates: a Monte Carlo study

ABSTRACT

We use grand canonical Monte Carlo simulations to examine the effect of the size of hydrate cavities (as reflected through the lattice constant of the hydrate unit cell) on the efficiency of clathrate hydrates in storing hydrogen gas. With this approach, the hydrate lattice is treated as a solid substrate where gas absorption takes place. Of practical interests are cases, where the lattice-size parameters are changed in such a way that they can promote/enhance multiple cavity occupancy, namely the presence of more than one guest-gas molecule in the same hydrate cavity. This phenomenon is commonly observed in the case of hydrogen hydrates and could increase their storage capacity. A parametric analysis is also carried out to quantify the correlation between the change in the lattice constant and the storage capacity since small changes in the size of the crystal unit cell may induce significant changes in the storage capacity especially in cases where multiple cavity occupancy occurs.     

On the influence of lattice vibrations on the tunnel-current in normal metals

Energy spectra of 50 kev-electrons scattered inelastically in thin Al foils of various thicknesses have been measured as a function of scattering angle. The measured angular distribution of electrons which have excited one or more volume plasmons is compared with theoretical calculations and good agreement is obtained. From the integrated intensities, the mean free path of 50 kev-electrons for plasmon excitation is determined with an accuracy of about 20%. The resulting value Λ=820 Å is in good agreement with the theoretical value calculated fromFerrell's free electron model (Λ=760Å).     

Saturation of the resistivity in metals with lattice instabilities

We correlate s-shape resistivity in A-15, C-15 and charge density wave compounds with structural instabilities. We propose that the exponential term of the resistivity is caused by the scattering against thermally excited molecular states. We show that this interpretation is supported by a large number of experimental data and naturally explains the apparent violation of Mathiessen's rule in irradiation experiments. Connections with recent theoretical developments on strong electron-phonon coupling are discussed.     

Diffusion of hydrogen in metals

The present status of our understanding of the diffusion of hydrogen in metals, both experimental and theoretical, is reviewed. Discussions are focused on the mechanism of diffusion of hydrogen isotopes H, D and T in f.c.c. and b.c.c. metals; the positive muon (μ ⁺) is referred to where appropriate. An up-to-date compilation of diffusion data as a function of temperature and isotope mass has been made, and a clear distinction in general diffusion behaviour in f.c.c. and b.c.c. metals is noted. Subsequently, the results obtained from the Gorsky effect, nuclear magnetic resonance and quasi-elastic neutron scattering that provide information on elementary jump processes are discussed.

A conceptual framework of the quantum diffusion of light interstitials in metals is given, including the recent Kondo theory that emphasizes the crucial importance of particle-conduction electron interactions in the diffusion process, especially at low temperatures. It is shown with the help of recent estimates of the tunneling matrix element that the overall feature of diffusion of hydrogen isotopes in b.c.c. metals as well as μ ⁺ in f.c.c. metals can be explained consistently within the frame presented here.

Finally, recent advances in the diffusion studies on hydrogen in b.c.c. metals are described. They include a re-analysis of quench-recovery experiments that manifested nearly athermal diffusion of H, D and T in Ta at low temperatures, and an enormous enhancement of the diffusivity under stress (superdiffusion) observed for H and D in V.     

Trends in hydrogen chemisorption on transition metals

A systematic study of H adsorption on the close-packed surfaces of the transition metals in the 3d and 4d series is presented. The effect of the TM d band on the chemisorption bond is investigated, by embedding a cluster of TM muffin tins at the surface of an effective jellium-like medium. It is found that the broad and incomplete H/jellium resonance is narrowed, shifted down and made to contain more electrons as a result of hybridization with the TM d states. These effects are larger in the case of the 4d metals, thus indicating a greater participation in the chemisorption bond of the d electrons for these metals than for the 3d metals. Calculation of one-electron energy differences on going from the H on jellium system to that of H on the TM cluster are presented. Trends for the one-electron energy differences are compared to trends in experimental chemisorption energy. H adsorption in the three-fold hollow site with no secondlayer TM atom below the H site is favoured for the hcp metals, while no discernible preference between the two hollow sites is recorded for the fcc metals, with the exception of Rh where the site with no second-layer TM atom below is preferred.     

Diffusion-controlled reaction on a one dimensional lattice: Dependence on jump and reaction probabilities

In an earlier study [J.C. Lewis, H. Wheeler, Physica A 271 (1999) 63–86] of the dependence on jump probability $p$ of the rates of diffusion-controlled reactions on simple cubic lattices in dimension $2\le d\le 4$ we found that the dependence was non-linear, which is not in accord with what would be expected on the basis of theories of such reactions in continua [M. von Smoluchowski, Wien. Ber. 124 (1915) 263; Phys. Zeit. 17 (1916) 557–585; Z. Phys. Chem. 92 (1917) 129; S. Chandrasekhar, Revs. Modern Phys. 15 (1) (1943) 1–89]. In the present work we examine the $d=1$ case. Jump probabilities less than one are of particular importance in that the $p=1$ case, in which all particles move simultaneously, is not physical.A recursive solution for the concentration of reactant $S$ as a function of time and of jump probability $0<p\le 1$ is developed for the coagulation reaction $S+S\to S$ in a one-dimensional lattice gas. This solution is exact for the case $p=1$. It reproduces the analytical form derived by Privman [V. Privman, Phys. Rev. E 50 (1) (1994) 50–53. Also available as arXiv.org preprint cond-mat/9310079v1], and gives excellent agreement with computer simulations for $p<1$. Kinetics for the annihilation reaction $S+S\to nothing$ are derived from the kinetics of the coagulation reaction $S+S\to S$ using Privman’s transformation in the above cited work.Using the recursive solution we are able to demonstrate data collapse for $p<1$.A quantitative measure for the effect of fluctuations caused by reaction using pair correlations of gap frequencies was developed and studied.     

Effect of three-body forces on the lattice dynamics of noble metals

A simple method to generate an effective electron-ion interaction pseudopotential from the energy wave number characteristic obtained by first principles calculations has been suggested. This effective potential has been used, in third order perturbation, to study the effect of three-body forces on the lattice dynamics of noble metals. It is found that three-body forces, in these metals, do play an important role. The inclusion of such three-body forces appreciably improves the agreement between the experimental and theoretical phonon dispersion curves.