[en] Solid breeder blankets with lithium ceramics as breeder and reduced activation ferritic martensitic (RAFM) steel as structural material require beryllium (Be) to increase the tritium breeding ratio (TBR) performance. In the event of plasma disruptions the values and distribution of induced currents in the breeding blanket will depend on the electrical resistivity of the adopted materials. The electrical conductivity of the insulating Be oxide layer on the pebbles surface could be significantly altered in the presence of a γ field as well as the electrical conductivity of the purging gas present inside the Be pebble bed assembly. In this paper we report the electrical properties of Be pebble beds under an irradiation environment with a γ radiation field ranging from 5x10⁴ to 1.3x10⁶ Gy/h at the Portuguese Research Reactor. Some Be pebbles were accommodated in a container where a typical purging gas of He+0.1% H₂, as foreseen in the blanket design, was introduced. The results show a decrease of the electrical resistivity values from 0.061 to 0.055 Ωm during the exposure in a γ field of 1.3x10⁶ Gy/h for the beds containing the purging gas mixture. The conductivity of the pebble bed without purging gas was not affected by the radiation. The results suggest that the radiation induced conductivity (RIC) was due to the ionization of the gas present in the bed

[en] A defect associated with Li in ZnO is reported. This is an optical system which absorbs strongly in the red part of the spectrum: a doublet, the zero phonon lines are at 1.884 and 1.879 eV, respectively. The chemical nature of the centre is identified through isotope substitution. This is the first observation of sharp optical features involving Li in ZnO. Although there are similarities to a Li EPR centre, we cannot yet correlate the optical centre. Similarities to a previously attributed system involving Ni are discussed

[en] The present study focusses on a stony meteorite found in the 90’s in North West Africa, that has not yet been classified. It was studied by optical microscopy, X-ray fluorescence, X-ray diffraction and Mössbauer spectroscopy. The Fe-bearing phases found by Mössbauer spectroscopy are consistent with the elements found by XRF measurements as well as with phases determined by XRD patterns. The RT spectrum is complex mainly due to the large linewidths of the lorentzians or to the distribution of sites that can obscure the presence of sextets or doublets. From the results obtained the classification of the NWAXX meteorite can be made to an achondrite Winonaite.

[en] Hafnium ions were implanted into calcium fluoride single crystals. The lattice damage introduced by the implantation was investigated with the Rutherford backscattering (RBS) channelling technique. The lattice location of the implanted ions was determined by performing channelling measurements for the <1 1 0> crystal direction. A comparison of the angular scan with Monte Carlo simulations leads to the conclusion that >90% of the Hf ions are on Ca sites directly after implantation. Subsequent annealing of the samples was performed in a rapid thermal annealing apparatus. Perturbed angular correlation (PAC) measurements with ¹⁸¹Hf(¹⁸¹Ta) show quadrupole interactions with ν_Q1 = 300(3) MHz (η = 0.00), ν_Q2 = 1285(13) MHz (η = 0.43) and ν_Q3 = 1035(10) MHz (η = 0.00) after annealing up to 1200 K.

[en] Zirconium oxynitride thin films were deposited by dc reactive magnetron sputtering. A zirconium metallic target was sputtered in an Ar + N₂ + O₂ atmosphere. Argon and nitrogen flow rates were maintained constant whereas oxygen was pulsed during the deposition, implementing the reactive gas pulsing process (RGPP). A constant pulsing period T = 3 s was used following an exponential periodic signal versus time. The introduction time of oxygen was systematically changed from 17% to 83% of the period. The RGPP allowed the synthesis of ZrO_xN_y films with tuneable metalloid concentrations adjusting the introduction time of the oxygen. Composition and structural variations associated with mechanical, optical and electrical properties exhibited a smooth transition, from metallic-like characteristics, typical of the fcc-ZrN phase, to semi-conducting behaviour corresponding to a mixture of orthorhombic-Zr₃N₄(O) and γ-Zr₂ON₂ crystalline phases.

[en] N, (N + Ga) and (N + Al) doped ZnO films were deposited on c-plane sapphire substrates by RF magnetron sputtering at room temperature. The samples were characterized by their structural, surface morphological, compositional and optical properties. The x-ray diffraction studies confirmed the co-doping of (N + Ga) and (N + Al) besides showing improvement in the crystallinity when compared with the single N doping. The surface of the films becomes rougher after co-doping. The x-ray photoelectron spectroscopy and Rutherford back-scattering analysis indicate that the co-doping changes the chemical states and varies the amount of nitrogen (N) in ZnO. The amount of 'N' has been greatly increased for (N + Ga) co-doping, indicating that it is the best co-doping pair for p-type ZnO. Additionally, co-doping has increased the average visible transmittance (40-650 nm) and the optical band gap is shifted towards shorter wavelength. In the case of (N + Al) co-doping, the band gap becomes wider than that of undoped ZnO

[en] Zirconium implantation-induced amorphization has been investigated with Rutherford back scattering spectrometry along a channeling direction (RBS-C) using 2 MeV He⁺. Ion implantation was carried out at the energy of 175 keV, with fluences of 2 x 10¹⁵ to 2 x 10¹⁶ Zr⁺/cm² at room temperatures. The critical amorphization fluence at room temperature was determined as ∝1.5 x 10¹⁶ Zr⁺/cm² corresponding to ∝ 40 dpa; ∝2.7% peak Zr-concentration which is a lower damage energy than that reported for implantation with ions of similar mass and energy. The effect of post implantation of oxygen into a pre-implanted sample (with zirconium) was investigated. The RBS results show that oxygen implantation in a crystalline sample increases the damage only slightly and slightly broadens the Zr profile. For the fluences above thresh-old for amorphization, post implantation by oxygen has very little effect on the residual damage or on the Zr distribution. The presence of both F and F+ centers were indicated by optical absorption (OA) measurements. The OA spectra show the concentration of F and F+ centers increases with increasing fluence with some changes resulting from oxygen implantation of a pre-zirconium-implanted sapphire. This alters the relative concentrations of F and F⁺ centers. The F-type center concentrations for the samples were calculated using Smakula's equation. Photoluminescence (PL) at an excitation of 255 nm confirms the presence of both F and F+ centers with emission peaks at about 420 and 325 nm respectively. The PL spectra suggest that oxygen implantation decrease the concentration of the both species, consistent with the OA results (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] Several polymorphs exist in alumina (Al_2O_3), and they transform to a stable α-phase with a hexagonal corundum structure on thermal annealing. This structural change is irreversible as a function of temperature, and transformation of corundum to another metastable crystalline phase has never been observed by heat treatments. In this study, we irradiated single crystals of Al_2O_3 with Zr ions and obtained an irradiated microstructure consisting of a buried α-Al_2O_3 layer surrounded on top and bottom by layers of a defect cubic spinel Al_2O_3 phase. We examined the thermal stability of this microstructure using transmission electron microscopy and X-ray diffraction. We found that the corundum phase completely transforms to the spinel phase following annealing at 1173 K for 1 h: the thermodynamically stable phase transforms to the metastable phase by heat treatments. We discuss this unusual structural change within the context of our results as well as previous observations

[en] The structure of single crystal α-Al₂O₃ irradiated with 175 keV zirconium ions to fluences of 7.5 × 10¹⁵ and 1.5 × 10¹⁶ Zr/cm² at room temperature, was investigated using Rutherford backscattering spectroscopy with ion channeling (RBS-C) and transmission electron microscopy (TEM). A buried amorphous layer was observed in samples irradiated at room temperature to a fluence of 1.5 × 10¹⁶ Zr⁺/cm² (175 keV). The buried amorphous region is sandwiched between two highly-damaged crystalline regions. Nano-beam electron diffraction confirmed that both the near-surface damaged layer and the deeper damaged layer remained crystalline, but the buried amorphous region is lacking in long-range atomic order. Post irradiation using 55 keV oxygen ions at room temperature into pre-Zr-implanted samples produced ion beam-induced epitaxial crystallization (IBIEC) of the amorphous region adjacent to the near-surface damaged layer. Growth of the metastable polymorph γ-Al₂O₃ was observed at the amorphous/near surface damaged crystalline interface, as a result of this oxygen ion irradiation

[en] Thin films containing monometallic (Ag,Au) and bimetallic (Ag–Au) noble nanoparticles were dispersed in TiO₂, using reactive magnetron sputtering and post-deposition thermal annealing. The influence of metal concentration and thermal annealing in the (micro)structural evolution of the films was studied, and its correlation with the localized surface plasmon resonance (LSPR) and surface enhanced Raman spectroscopy (SERS) behaviours was evaluated. The Ag/TiO₂ films presented columnar to granular microstructures, developing Ag clusters at the surface for higher annealing temperatures. In some cases, the films presented dendrite-type fractal geometry, which led to an almost flat broadband optical response. The Au/TiO₂ system revealed denser microstructures, with Au nanoparticles dispersed in the matrix, whose size increased with annealing temperature. This microstructure led to the appearance of LSPR bands, although some Au segregation to the surface hindered this effect for higher concentrations. The structural results of the Ag–Au/TiO₂ system suggested the formation of bimetallic Ag–Au nanoparticles, which presence was supported by the appearance of a single narrow LSPR band. In addition, the Raman spectra of Rhodamine-6G demonstrated the viability of these systems for SERS applications, with some indication that the Ag/TiO₂ system might be preferential, contrasting to the notorious behaviour of the bimetallic system in terms of LSPR response. (paper)