The gold-zirconia yolk-shell system is an interesting catalyst for CO oxidation. The size distribution of the gold nanoparticles is very narrow, and they are well separated from each other also after treatment at high temperature, which is due to their encapsulation in crystalline zirconia hollow spheres. Because this allows thermal and chemical treatment without affecting the size distribution, different defect structures of the gold nanoparticles can be induced, and the effect on catalytic activity can be investigated. Line profile analysis of the powder diffraction data based on the whole powder pattern modeling approach was used to determine the domain size distribution and lattice defects present in this two-phase system. The influence of different diffractometer setups on the results of the line profile analysis was also investigated. Variation of the chemical and thermal treatment procedures allowed altering the microstructure of the system. The resulting catalysts showed substantial variation in the activity for CO oxidation. Lower dislocation densities and less stacking faults result in decreased catalytic activity. These contributions to activity could be studied without any superimposed size effect due to the constant gold particle sizes.

A detailed study of the near-surface structure and composition of Nb, the material of choice for superconducting radio-frequency accelerator (SRF) cavities, is of great importance in order to understand the effects of different treatments applied during cavity production. By means of surface-sensitive techniques such as grazing incidence diffuse x-ray scattering, x-ray reflectivity, and x-ray photoelectron spectroscopy, single-crystalline Nb(100) samples were investigated in and ex situ during annealing in an ultrahigh vacuum as well as in nitrogen atmospheres with temperatures and pressures similar to the ones employed in real Nb cavity treatments. Annealing of Nb specimens up to 800°C in a vacuum promotes a partial reduction of the natural surface oxides (Nb 2 O 5 , NbO 2 , and NbO) into NbO. Upon cooling to 120°C, no evidence of nitrogen-rich layers was detected after nitrogen exposure times of up to 48 h. An oxygen enrichment below the Nb-oxide interface and posterior diffusion of oxygen species towards the Nb matrix, along with a partial reduction of the natural surface oxides, was observed upon a stepwise annealing up to 250°C. Nitrogen introduction to the system at 250°C promotes neither N diffusion into the Nb matrix nor the formation of new surface layers. Upon further heating to 500°C in a nitrogen atmosphere, the growth of a new subsurface Nb x N y layer was detected. These results shed light on the composition of the near-surface region of Nb after low-temperature nitrogen treatments, which are reported to lead to a performance enhancement of SRF cavities.

(100) oriented niobium (Nb) crystals annealed in the vacuum conditions close to that used in mass production of 1.3 GHz superconducting radio-frequency cavities for linear accelerators, and treated in nitrogen at a partial pressure of 0.04 mbar at temperatures of 800 °C and 900 °C have been studied. The surfaces of the nitrogen-treated samples were investigated by means of various surface-sensitive techniques, including grazing-incidence X-ray diffraction, X-ray photoemission spectroscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy in planar view and on cross-sections prepared by a focused ion beam. The appearance of a dense layer of epitaxial rectangular precipitates has been observed for the Niobium nitrided at 900°C. Increased nitrogen concentration in the near surface region was detected by glow-discharge optical-emission spectroscopy, focused ion-beam cross-sectional images and X-ray photoelectron spectroscopy. Crystalline phases of NbO and β-Nb 2 N were identified by X-ray diffraction. This information was confirmed by X-ray photoelectron measurements, which in addition revealed the presence of Nb 2 O 5 , NbON, NbN and NbN x O y components on the surface. These results establish the near-surface Nb phase composition after high-temperature nitrogen treatment, which is important for obtaining a better understanding of the improved RF cavity performance.

Noble-metal-free functional oxides are active catalysts for CO oxidation at low temperatures. Spinel-type cobalt oxide (Co 3 O 4 ) nanoparticles can be easily synthesized by impregnation of activated carbon with concentrated cobalt nitrate and successive carbon burn off. Mean size and particle size distribution can be tuned by adding small amounts of silica to the carbon precursor, as witnessed by whole powder pattern modeling of the X-ray powder diffraction data. The catalytic tests performed after silica removal show a significant influence of the mean domain size and of size distribution on the CO oxidation activity of the individual Co 3 O 4 specimens, whereas defects play a less important role in the present case.