Interaction of hydrogen isotopes with metals: Deuterium trapped at lattice defects in palladium

From an interplay between theory based on the effective-medium scheme and experiments, an extremely simple picture has evolved which is capable of describing a vast number of experimental quantities related to interaction of hydrogen with metals, especially the trapping of hydrogen at defects. It is shown that the trap strengths are determined mainly by the interstitial electron density, and any open structures in the lattice leads to a trap, with the vacancies and voids being the strongest traps. It is also found theoretically and experimentally that up to six hydrogen atoms can be accomodated in a vacancy, and the change in trap strengths with occupancy has been determined. Recent results for the trapping of deuterium to defects in Pd are discussed.     

Dechanneling by lattice defects

Backscattering measurements were used to study the dechanneling of ¹H⁺ and ⁴He⁺ ions in irradiated crystals of Al and Cu. The effect of the annealing of self-interstitials and vacancies on dechanneling was correlated with the formation of Al-Ag mixed dumbbells and vacancy-Sn atom complexes in dilute alloys of Al. The depth profile of damage produced in Al-0.1 at.% Ag by 0.5 MeV He⁺ irradiation was measured by ¹H⁺ dechanneling. The rate of dechanneling of ¹H⁺ ions in ⁴H⁺-irradiated Al-0.1 at.% Ag Cu-0.06 at.% Au and Cu-0.25 at.% Be crystals exhibited ion energy dependences between E^?0.5 and E^?0.9. Dechanneling from small defect clusters in Cu-0.06 at.% Au increased linearly with increasing sample temperature. The dechanneling cross-sections for Al-Ag mixed dumbbells in Al, and Cu-Be mixed dumbbells in Cu were σ_d～- 8 × 10^?18 cm². The results were compared with dechanneling theories.     

Penetration of deuterium from plasma through a nickel membrane

Institute of Physical Chemistry, Russian Academy of Sciences. Translated from Atomnaya énergiya, Vol. 76, No. 2, pp. 145–148, February, 1994.     

Reemission measurements of surface recombination for deuterium on nickel

The reemission of D₂ molecules during implantation of 60 keV D₃⁺ was studied with samples of polycrystalline nickel in the temperature range of 450–880 K, where recombination is the ratelimiting step of reemission. The experimental results together with computer calculations were used to evaluate surface recombination rate coefficients, which are consistent with those obtained in previous permeation measurements.The data are also discussed with respect to existing model calculations.     

Production of defects in molybdenum by a deuterium glow discharge plasma

Conclusions Cathode bombardment of monocrystalline molybdenum surfaces oriented perpendicular to the [111] direction in a deuterium glow discharge plasma at a burning voltage of 500 V with a discharge current density of 4.5 mA/cm² and a temperature of 800°C leads to formation in the surface layer of edge and nearly edge loops with Burgers vectors b=a/2 111 lying in the {111} and {321} planes and the Burgers vectors b=a 100 lying in the {100}, {115}, and {117} planes. All loops with diameters >100 Å were injection loops. It is proposed that the smaller defects that can be seen in an electron microscope are also aggregates of interstitial atoms. The formation of dislocation loops with Burgers vectorsb=a 100 has been explained in terms of the large compressive stresses which arise in the surface layer of the foil during bombardment. The production of a large number of highly mobile interstitial atoms in the surface layer of a single crystal by the deuterium plasma and their subsequent diffusion to sinks probably play a dominant role in radiation-enhanced self- and heterogeneous diffusion.Translated from Atomnaya Énergiya, Vol. 48, No. 3, pp. 157–161, March, 1980.     

Thermal desorption of helium from defects in nickel

Helium atoms, introduced into materials by helium plasma or generated by the (n, α) nuclear reaction, have a strong tendency to accumulate at trapping sites such as vacancy clusters and dislocations. In this paper, the effects of dislocations, single vacancies and vacancy clusters on the retention and desorption of helium atoms in nickel were studied. Low energy (0.1-0.15 keV) helium atoms were implanted in nickel with vacancies or dislocations without causing any displacement damage. He atoms, interstitial-type dislocation loops, and vacancy clusters were also introduced with irradiation damage by 5.0 keV helium ions. Helium thermal desorption peaks from dislocations, helium-vacancy clusters and helium bubbles were obtained by thermal desorption spectroscopy at 940 K, in the range from 900 to 1370 K, and at 1500 K, respectively. In addition, a thermally quasi-stable state was found for helium-vacancy clusters.     

Dechanneling of fast particles by lattice defects

Channeling is one of the numerous phenomena occurring near the surface of any crystalline material irradiated by fast particles. Dechanneling by lattice defects - and in particular by the defects created by the irradiation itself - may play a significant role in such phenomena as sputtering and blistering. It is first shown that dechanneling can be due to an obstruction, to the deformation of the lattice or to both simultaneously. Results of calculations of dechanneling cross sections for some defects are presented. Experimental evidence of dechanneling is described for such defects as (1) grain (or twin) boundaries, (2) stacking faults, (3) dislocations, (4) interstitial atoms, (5) radiation-induced defects, (6) gas bubbles, (7) Guinier-Preston zones, and (8) anti-phase boundaries. Dechanneling cross sections have been measured accurately in cases (1)–(4). The experimental values are in very satisfactory agreement with the theoretical estimates. For example, the dechanneling width of a straight dislocation, in aluminium, for α-particles (5 MeV) channeled along {111} planes, is found to be equal to $\text{140 ± 40}$ Å, whereas calculation gives 175 Å.     

Interaction between implanted fluorine atoms and point defects in preamorphized silicon

We have studied, by means of B diffusion analyses, the effect of F on the point defect density in preamorphized Si. Through molecular beam epitaxy (MBE) Si samples containing a special B multi-spike were grown. These samples were amorphized to a depth of 550 nm by implanting Si at liquid nitrogen temperature and then enriched with F at different energies (65–150 keV) and fluences (0.7–5 × 10¹⁴/cm²). After solid phase epitaxy (SPE) of the samples, we induced, by thermal annealing at 850 °C, the emission of Si self-interstitials (Is) from the end-of-range (EOR) defects. We studied the diffusion of the B spikes, demonstrating that F effectively reduces the B diffusion. This reduction is shown to be caused not by a direct B–F chemical interaction, but by a F interaction with point defects. In particular, F is able to reduce the density of Is, which are responsible for the B diffusion. Still, we showed that F does not appreciably influence the Is emission from the EOR defects, but a local interaction occurs between F atoms and Is after the release of these defects from the EOR region. This interaction results in a consistent reduction of B diffusivity in F enriched regions.     

Experimental study on cold fusion using deuterium gas and deuterium ion beam with palladium

A series of experiments using deuterium gas and low energy deuteron beam with palladium has been designed at Mississippi State University to allow for the observation, if it exists, of cold fusion. Three experiments were performed. One involved the diffusion transient of deuterium gas into palladium. The gas was cooled by liquid nitrogen, and its temperature was permitted to rise to room temperature, changing from near –34°C to 19°C in 75 minutes. A spherical lithium neutron detector, 21 cm from the palladium, gave an audible indication of neutron levels approximately twice the background. A second experiment used a deuterium ion beam (1 kev) which bombarded a palladium target. An average counting rate of 36±6 counts for 2 minutes was measured by a BF₃ tube with a paraffin moderator, 50 cm from the target. The background varied from 1–7 counts for each 2 minutes of counting period and averaged 4±2 counts in 2 minutes. A nitrogen ion beam impinging on the same palladium target produced 6 counts for a 2-minute counting period. A third experiment used a hydrogen ion beam first, then a nitrogen ion beam, finally a deuterium ion beam to bombard the same palladium target. These ion beams had energy less than 1 kev, and created neutron counts in the range of background. The palladium specimens were a piece of foil and a tube which used to be the palladium leak in a neutron generator. These preliminary experiments will be repeated, improved, and extended later.     

Behavior of tungsten with exposure to deuterium plasmas

Four kinds of tungsten (W) materials, i.e. (1) foil of 50 μm thick (f-W), (2) polycrystalline (Pc-W) with grain size of ∼3 μm, (3) recrystallized (Re-W) with grain size of ∼50 μm and (4) vacuum plasma spraying (VPS-W) coatings, were irradiated employing linear plasma generators, with fluxes ?1 × 10²² D/m²/s and energies ?100 eV/D. Scanning electron microscopy (SEM) was used to observe blister formation at the surfaces. The SEM surface morphology and cross section observation indicates that blister formation is related to the microstructure and surface state of different material grades. Results of trapping and deuterium retention measured by thermal desorption spectroscopy (TDS) and nuclear reaction analysis (NRA) show also a close correlation between the retention and the microstructure and surface state.     

The solubility of deuterium in lithium-lead alloys

The solubility of deuterium in lithium-lead alloys was measured as a function of temperature and atomic fraction of lithium, X_Li. It was found that, at the atom fraction X_Li = 0.78, corresponding to the composition “Li₇Pb₂”, the solubility in the solid phase is lower by a factor of a few hundred than that in the liquid phase. The solubility of deuterium in the Li-Pb system decreases drastically with decreasing X_Li. At about X_{Li = 0.17}, which corresponds to the eutectic “Li₁₇Pb₈₃”, the solubility is independent of temperature. The transition from exothermal to endothermal dissolution occurred at about X_Li ? 0.17.     

Instability of diatomic deuterium in fcc palladium

To clarify some of the solid-state aspects of cold fusion in deuterated transition metal electrodes, we have carried out first-principles self-consistent total energy calculations for various configurations of atomic and diatomic deuterium inside fcc palladium. We find that the stability of the Pd+D system is controlled by the relative position of the deuterium-inducedantibonding level with respect to the Fermi energy. The equilibrium D-D distance in dense PdD up to =3 is found to be much larger than the free space value. The calculated Born-Oppenheimer energy surface of diatomic D₂ in crystalline palladiuim is shown to have but metastable local minima whose internuclear separation is at least 0.2 Ålarger than that of the isolated D₂ molecule. We conclude that D₂ incrystalline Pd will have a substantially lower tunneling probability than hitherto thought and that explanation for fusion mechanisms should be sought elsewhere.