No abstract

The lithium-intercalated fulleride Li 12 C 60 was investigated in view of a lightweight hydrogen storage material due to the low molecular weight of its constituents. Deuterium (D 2 ) absorption in Li 12 C 60 shows an uptake of up to 9.5 mass % D 2 (equivalent to ∼5 mass % H 2 for the same stoichiometry). Under a pressure of 190 bar the onset of absorption was observed at a temperature below 100 °C, which is 200 °C lower than that for pure C 60 . Deuterium desorption was investigated by in-situ neutron powder diffraction, and at a pressure of 1 bar desorption was observed above 300 °C. The ab/desorption is accompanied by a partial de/reintercalation of lithium, observed by the appearance and disappearance of LiD reflections after absorption and during desorption, respectively. A minor part of deuterium is present in ionic form in LiD, and the major part is covalently bound in a Li-depleted compound Li 12−x C 60 D 36+y .

No abstract

Because of its light weight and small size, hydrogen exhibits one of the fastest diffusion rates in solid materials, comparable to the diffusion rate of liquid water molecules at room temperature. The diffusion rate is determined by an intricate combination of quantum effects and dynamic interplay with the displacement of host atoms that is still only partially understood. Here we present direct observations of the spatial and temporal changes in the diffusion-induced concentration profiles in a vanadium single crystal and we show that the results represent the experimental counterpart of the full time and spatial solution of Fick's diffusion equation. We validate the approach by determining the diffusion rate of hydrogen in a single crystal vanadium (001) film, with net diffusion in the [110] direction.

Grazing incidence neutron scattering experiments offer surface sensitivity by reflecting from an interface at momentum transfers close to total external reflection. Under these conditions the penetration depth is strongly non-linear and may change by many orders of magnitude. This fact imposes severe challenges for depth resolved experiments, since the brilliance of neutron beams is relatively low in comparison to e.g. synchrotron radiation. In this article we use probability density functions to calculate the contribution of scattering at different distances from an interface to the intensities registered on the detector. Our method has the particular advantage that the depth sensitivity is directly extracted from the scattering pattern itself. Hence for perfectly known samples exact resolution functions can be calculated and visa versa. We show that any tails in the resolution function, e.g. Gaussian shaped, hinders depth resolved experiments. More importantly we provide means for a descriptive statistical analysis of detector images with respect to the scattering contributions and show that even for perfect resolution near surface scattering is hardly accessible.