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Abnormal permeation behavior of hydrogen through niobium has been investigated in this paper, i.e. the permeation flux saturated with long-term decrease after reaching a maximum. The diffusivity and permeability have been deduced from the decay edge of permeation transient. Three kinds of polycrystalline niobium foils with different annealing temperature have been compared, to verify the effect of defects and grain properties on the permeability and diffusivity. In the temperature range of (773–1023) K, the heat treatment along with the permeation cycles could either reduce or increase the permeability and diffusivity depending sensitively on temperature and showing a temperature threshold around 950 K. The permeation flux is proportional to square root of pressure, revealing that the abnormal permeation was still bulk diffusion-limited. The diffusivity gradually decreased with permeation cycles, and became more and more sensitive to pressure. The niobium foil expanded macroscopically along the gradient of hydrogen concentration, which reveals the strong and unrecoverable lattice distortion in this temperature and pressure range. The X-ray diffraction studies showed that splitting of all the Nb peaks and shifting of Nb-D peaks along with hydrogen loadings. The phase transition was expected to eliminate the lattice strain during hydrogen loading and which in turn acted as a diffusion barrier.

Surface modification of tungsten due to the cooling species nitrogen seeded in the divertor region, i.e., by nitrogen ion implantation or re-deposition, is considered to affect the permeation behavior of H isotopes. This work focuses on the effect of nitrogen ion implantation into tungsten (W-N) on the deuterium gas-driven permeation behavior. For comparison, both permeation in tungsten implanted with W ion (W-W) and without implantation (pristine W) are studied. These three samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photo-electron spectroscopy (XPS). The SEM results revealed that the W-W sample has various voids on the surface, and the W-N sample has a rough surface with pretty fine microstructures. These are different from the pristine W sample with a smooth and compact surface. The XRD patterns show the disappearance of crystallinity on both W-W and W-N sample surfaces. It indicates that the ion implantation process results in an almost complete conversion from crystalline to amorphous in the sample surfaces. The sputter-depth profiling XPS spectra show that the implanted nitrogen prefers to form a 140 nm thick tungsten nitride layer. In permeation experiments, it was found that the D permeability is temperature dependent. Interestingly, the W-N sample presented a lower D permeability than the W-W sample, but higher than the pristine W sample. Such behavior implies that tungsten nitride acts as a permeation barrier, while defects created by ions implantation can promote permeability. The possible permeation mechanism correlated with sample surface composition and microstructure is consequently discussed in this work.

Thermal desorption spectroscopy (TDS) measurement of tungsten (W) exposed to tritium (T2) under a series of conditions was conducted, and the peak of T2 desorption reached as high as 895 K at the heating rate of 20 K/min. The detrapping energy of T in W was then determined experimentally to be 2.18 ± 0.22 eV, suggesting that T was mainly trapped by vacancy clusters which may be formed during manufacturing and enhanced by charged T atoms.

The microstructure of tungsten, a primary candidate for the first wall of Tokamak devices, affects the retention and permeation of hydrogen isotopes. These have a close connection to the tritium inventory. In this work, the tungsten microstructure was tuned by annealing and intense 15,700 displacements per atom (dpa) keV-W-self-ion implantation. The samples were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The results reveal that the annealing treatment has little influence on the crystallite size but decreases the number of defects such as vacancies, which relates to the bulk microstructure. Moreover, ion implantation changes the sample surface from a smooth quasi-mirror to a grey morphology with various voids. The deuterium retention is suppressed by the decrease of bulk defects due to annealing, but does not present a saturation with the displacement damage increase. It is interesting to note that in permeation, the rate limiting step is bulk diffusion while the deuterium permeability is enhanced for samples with a surface modification. The possible permeation mechanisms and their relation with the sample microstructure are discussed in this work.

TiO2 powder was modified by the afterglow of plasma of pure N2 or H2, and mixed N2 + H2 gas. The ion species in plasma afterglow were measured by an ion-energy analyzer. It is found that the main ion is N2+ in N2 afterglow and the yield is changed to NH4+ with a six times higher concentration, when 10% H2 was input. The modified TiO2 shows significant differences of microstructure and optical properties depending on the plasma gas used. This work enables one to find a correlation between active species in the plasma afterglow and TiO2 microstructure/optical properties.

International audience; Rare earth (RE) ions doped in Si-based materials, compatible with Si technology, are promising compounds with regards to optical communication and energy conversion. In this article, we show the emission properties of Nd-doped Si-rich Si oxynitride (Nd-SRSON) films, and their dependence on the dangling bond density and the nature of the sensitizer. These films were prepared by reactive magnetron sputtering and post-annealing. The film composition, microstructure, and emission properties were investigated as a function of deposition parameters and annealing temperatures. Both Fourier transform infrared (FTIR) and ellipsometry spectroscopy measurements have confirmed that the sample composition (Si/N ratio) can be carefully tuned by varying the ratio of reactive nitrogen to argon in the sputtering plasma. Moreover, FTIR and x-ray photoelectron spectroscopy measurements demonstrate the existence of both nitrogen and oxygen dangling bonds (N· and O·) in as-deposited samples. These dangling bonds were passivated during annealing. Under non-resonant excitation at 488 nm, the films exhibit a significant photoluminescence (PL) signal from Nd3+ ions demonstrating the occurrence of an effective sensitization of Nd$^{3+}$ ions in the host matrix. Both PL excitation and ellipsometry results (the energy band gap from new amorphous model) exclude the sensitization by an exciton with energy over the band gap, whereas the presence of Si agglomerates, at the atomic scale, have been identified as effective sensitizers towards Nd$^{3+}$ ions. This work not only provides knowledge to optimize Si-based materials for favorable emission properties, but also, presents a universal methodology to investigate the nature of sensitizers for RE emitters. This allows one to find correlations between composition, microstructure, and emission properties.

One-dimensional tubes and rough-sphere particles of Fe-Co Prussian blue analogue with different structures were prepared from the cationic surfactant cetyltrimethyl ammonium bromide in an ethanol and water solution. The products were characterized by x-ray diffraction, energy-dispersive x-ray spectroscopy, infrared spectrum, transmission electron microscopy, field emission scanning electron microscopy, and vector network analysis. The experimental results clearly show that the reaction temperature is the dominant processing factor in controlling the morphologies of the resulting products. These compounds mainly consist of an Fe2+-CN-Co2+ entity, but some of them would be converted into Fe2+-CN-Co3+ with the addition of RbCl. The real parts of permeability (ϵ′) of these samples with different structures are in the range from 2.4 to 3.9. Furthermore, the synthesis mechanism and the influencing factors on dielectric properties are discussed.

Mn-Zn ferrite nanoparticles about 15 nm with various amounts of Co substituting for Mn were synthesized in microemulsion at 50°C. The samples were characterized by energy-dispersive X-ray spectroscopy, X-ray diffraction, scanning electron microscope, and vibrating sample magnetometer. The experimental results indicate the formula for all samples can be derived as CoxMn1−xZn0.5Fe1.504, and the presence of single-phase spinel ferrite is in all the samples without annealing at high temperature. The saturation magnetization increases with Co content (x = 0 to 0.31) followed by a decrease with further enhancement of Co (x = 0.39 and 0.48). Compared with that of Mn-Zn ferrite annealed at 600°C for 4 h, the saturation magnetization of the synthesis sample without annealing is larger, but the coercivity force is smaller.

We synthesized a series of cobalt-iron Prussian blue analogues in the form of nanocubes with which we tuned the amount of Cesium cation in the tetrahedral sites of the structure and varied nature of the alkali cation in the compound adopting a single microemulsion technique. Structure and morphology of the compound had been investigated by combining energy-dispersive X-ray spectroscopy (EDS), inductively coupled plasma (ICP), thermo-gravimetry analysis (TGA), infrared spectroscopy (IR), powder X-ray diffraction (XRD) and Transmission electron microscopy experiments (TEM). To directly determine the coercivity, remanence and Curie temperature, superconducting quantum interference device magnetometer (SQUID) was performed. Our investigation suggests that the amount and nature of the alkali cation are critical parameters for understanding the magnetic properties of the nanoparticles.