Nanohardness and brittleness of irradiated spinel ceramics

International audienceThe influence of the size of crystalline regions on mechanical properties of irradiated oxides has been studied using magnesium aluminate spinel MgAl2O4. The samples characterized by different dimensions of crystalline domains, from sintered ceramics with grains of few micrometers in size up to single crystals, were used in the experiments. The samples were irradiated at room temperature with 320 keV Ar2+ ions up to fluences reaching 5 × 1016 cm−2. Nanomechanical properties were measured by using a nanoindentation technique and the resistance to crack formation by measurement of the total crack lengths made by Vickers indenter. The results revealed: correlation of nanohardness with accumulated damage, radiation-induced hardness increase in grain-boundary region and significant improvement of material resistance to crack formation

HRTEM study of track evolution in 120-MeV U irradiated Gd2Ti2O7

High resolution Scanning Transmission Electron Microscopy (HRTEM) experiments were performed on Gd2Ti2O7 pyrochlore irradiated with 120-MeV U ions. A judicious choice of irradiation energy, sample preparation (using Focused Ion Beam) and analytical technique (HRTEM) allowed us to visualize the complete evolution of tracks from the surface of samples down to depths exceeding the projected range of irradiating ions. Such features as variation of track diameters, changes in track directions and discontinuous segments of tracks were clearly documented at various depths. By using two different scanning transmission electron microscopy (STEM) imaging modes: High- and Low-Angle Annular Dark Field imaging (HAADF and LAADF), it was possible to observe the radial substructure of tracks composed of an amorphous core surrounded by a damaged and strained crystalline envelope

Effect of combined local variations in elastic and inelastic energy losses on the morphology of tracks in ion-irradiated materials

Detailed analysis of the morphology of latent tracks created by swift heavy ions from the surface entry point on a pyrochlore crystal to the end of the ion trajectory reveals continuous changes in the track diameter as a function of ion deceleration, loss of track parallelism beyond a certain depth and the evolution from continuous to discontinuous tracks. The tracks exhibit a layered structure composed of a non-crystalline core surrounded by a strained crystalline envelope. Furthermore, surprising local increases in the diameter of the latent tracks are readily observed. This feature can be interpreted using a model based on the concept of effective local energy deposition, defined as the sum of the inelastic energy deposited by the swift track-forming ion and the elastic energy deposited by a primary knock-on atom inside the ion track. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Structural stability of Nd2Zr2O7 pyrochlore ion-irradiated in a broad energy range

The phase transformations induced by electronic excitation (Se) and ballistic processes (Sn) in Nd2Zr2O7 pyrochlores irradiated with heavy ions in three domains of energy (∼1 GeV, ∼100 MeV and a few MeV) were investigated by X-ray diffraction, Raman spectroscopy and transmission electron microscopy. In the Se regime at high energy, results show that: (i) ion tracks are formed above a Se threshold of 12.5 keV nm−1; (ii) both pyrochlore → anion-deficient fluorite phase transition and amorphization occur; (iii) total amorphization is always observed at the highest fluences; (iv) the internal structure (amount of amorphous phase vs. its anion-deficient fluorite counterpart) and the diameter of tracks depend on many parameters such as Se, the deposited energy density and the recrystallization rate. For irradiations performed with low-energy ions in the Sn regime, only the anion-deficient fluorite phase is formed up to a dose of 40 dpa. Thus Nd2Zr2O7 exhibits an unusual behaviour since this compound is amorphizable by Se and non-amorphizable by Sn. Annealing of totally amorphized Nd2Zr2O7 samples reveals strong differences in the recovery processes with other pyrochlore materials that are related to their different chemical compositions

Luminescence analysis of damage accumulation; case study of calcium molybdate

International audienceA comparative study of damage accumulation in calcium molybdate (CaMoO4) has been conducted using Rutherford Backscattering/Channeling (RBS/C), cathodoluminescence (CL) and ionoluminescence (IL) techniques. All methods used confirm a two-step character of damage build-up process. Similar threshold fiuence values have been extracted from RBS/C, CL and IL measurements. This analysis confirms the huge potential of luminescence techniques for damage analysis in single- and polycrystalline samples and the ability of the IL method to perform fast, in situ analysis of damage accumulation process. (C) 2014 Elsevier B.V. All rights reserved

Monte Carlo simulations of channeling spectra recorded for samples containing complex defects

The aim of the present paper is to describe the current status of the development of McChasy, a Monte Carlo simulation code, to make it suitable for the analysis of dislocations and dislocation loops in crystals. Such factors like the shape of the bent channel and geometrical distortions of the crystalline structure in the vicinity of dislocation has been discussed. The results obtained demonstrate that the new procedure applied to the spectra recorded on crystals containing dislocation yields damage profiles which are independent of the energy of the analyzing beam. (C) 2011 Elsevier B.V. All rights reserved

When eutectics meet plasmonics: Nanoplasmonic, volumetric, self-organized, silver-based eutectic

9 pags.; figs.© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Due to the development of novel manufacturing technologies and the increasing availability of nano-/micromaterials, plasmonics has become an emerging field in photonics research. Although the fabrication of metallic elements has already been widely demonstrated, the development of 3D plasmonic materials is progressing slowly. This paper reports the development of a self-organized, 3D nanoplasmonic eutectic composite that exhibits localized surface plasmon resonance at 595 nm. This eutectic composite is produced by directional solidification with the micro-pulling-down method and consists of a 3D, multiscale network of silver, nanometer-thick, micron-long sheets, and triangular cross-section microprecipitates embedded in a crystalline bismuth oxide matrix. Annealing at 600 °C further refined the structure and introduced metallic nanoparticles that exhibited plasmonic resonance in the optical region of the spectrum. This is the first demonstration of plasmonic behavior in a eutectic-based composite, which is engineered specifically for this purpose using a self-organization mechanism.he authors thank the Maestro Project (2011/02/A/ST5/00471) and the Preludium Project (2012/07/N/ST5/02428) from the National Science Centre, the Project operated within the Foundation for Polish Science Team Programme cofinanced by the EU European Regional Development Fund and the AFOSR Project 14RT0477: NOE Novel metamaterials and plasmonic materials properties enabled by the directional Eutectic solidification for support of this work.Peer Reviewe