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Cubic zirconia single-crystals (yttria-stabilized zirconia (YSZ)) have been irradiated with 4MeV Au2+ ions in a broad fluence range (namely from 5×1012 to 2×1016 cm-2) and at five temperatures: 80, 300, 573, 773, and 1073 K. Irradiated samples have been characterized by Rutherford backscattering spectroscopy in channeling mode, X-ray diffraction and transmission electron microscopy techniques in order to determine the disordering kinetics. All experimental results show that, whatever is the irradiation temperature, the damage build-up follows a multi-step process. In addition, the disorder level at high fluence is very similar for all temperatures. Thus, no enhanced dynamic annealing process is observed. On the other hand, transitions in the damage accumulation process occur earlier in fluence with increasing temperature. It is shown that temperature as low as 573K is sufficient to accelerate the disordering process in ion-irradiated YSZ. [ABSTRACT FROM AUTHOR]

This work reports the study, via the combination of Rutherford backscattering spectrometry and channeling, x-ray diffraction, and transmission electron microscopy experiments, of the damage formation in cubic yttria-stabilized zirconia single crystals irradiated with medium-energy (4 MeV) heavy (Au) ions. The damage buildup, which is accounted for in the framework of the multistep damage accumulation model, occurs in three steps. The first step at low fluences (up to 1015 cm-2), characterized by a regular increase in both the damage yield and the elastic strain, is related to the formation of small defect clusters. The second step in the intermediate fluence range (from 1015 to 5×1015 cm-2) leads to a sharp increase in the damage yield and to a large drop of the strain due to the formation of dislocation loops which collapse into a network of tangled dislocations. The third step at high fluences (above 5×1015 cm-2) exhibits a surprising decrease in the damage yield, which may be attributed to the reorganization of the dislocation network that leads to the formation of weakly damaged regions with a size of the order of 100 nm. [ABSTRACT FROM AUTHOR]

This article presents a study of the damage production in yttria-stabilized cubic zirconia single crystals irradiated with swift heavy ions. The combination of techniques which probe the material at different spatial scales (Rutherford backscattering spectrometry in channeling geometry, x-ray diffraction, transmission electron microscopy, and atomic force microscopy) was used in order to gain information about the damage depth distribution, the disordering buildup, the nature of radiation defects, and the occurrence of microstructural modifications. The damage results from the formation of tracks, due to the huge electronic excitations induced in the wake of incident ions. The melting of the material in the core of tracks, via a thermal spike mechanism, leads to the creation of large hillocks at the surface of the crystals. The overlapping of ion tracks at high fluence (above ∼1012 cm-2) induces a severe transformation of the microstructure of the material. Nanodomains slightly disoriented from the main crystallographic direction are formed, with a size decreasing with increasing irradiation fluence. These results may be used to predict the damage evolution in other nonamorphizable ceramics irradiated with swift heavy ions. [ABSTRACT FROM AUTHOR]

The micro-structural modifications produced in MgO single crystals exposed to medium-energy heavy ions (1.2-MeV Au) were investigated using Rutherford backscattering spectrometry in channeling geometry coupled to Monte-Carlo analyses, secondary ion mass spectrometry, X-ray diffraction and transmission electron microscopy. The damage accumulation and the elastic strain variation were interpreted in the framework of the multi-step damage accumulation (MSDA) model. Both build-ups follow a multi-step process similar to that recently observed for ion-irradiated yttria-stabilized zirconia (YSZ) single crystals. However, in MgO, an unexpectedly high disorder level occurs far beyond the theoretical damage distribution. These results strongly suggest that the migration of defects created in the near-surface layer is most likely at the origin of the broadening of the damage depth distribution in MgO. [ABSTRACT FROM AUTHOR]

Abstract: Yttria-stabilized zirconia (YSZ) single crystals were irradiated with 4-MeV Au ions at several temperatures from RT up to 800°C. For each temperature, the amount of damage created by irradiation was measured as a function of the ion fluence by Rutherford backscattering spectrometry in channeling geometry (RBS/C). In all cases the damage exhibits a peak around the ion projected range (∼500nm) and it accumulates via a multi-step process. Furthermore, the damage build-up strongly depends on the irradiation temperature: the occurrence of the second stage of damage accumulation, which presents a high increase of the damage fraction, is shifted towards lower fluences as the temperature is increased. This effect may be explained by enhanced defect-clustering at high temperature. [Copyright &y& Elsevier]

Abstract: A2B2O7 pyrochlores (zirconates with A=Gd, Nd, Sm or Eu, and a titanate Gd2Ti2O7) were irradiated with swift heavy ions in order to investigate the effects of the chemical composition on the structural changes induced by high electronic excitation. XRD results show that the structural modifications induced by irradiation with 119MeV U ions are strongly dependent on the sample composition: Gd2Ti2O7 is readily amorphized, whereas Gd2Zr2O7 is transformed into a radiation-resistant anion-deficient fluorite structure. For Sm2Zr2O7, Eu2Zr2O7 and Nd2Zr2O7, a more complex behavior is observed since both a pyrochlore–fluorite phase transformation and amorphization occur. The results suggest that an ion track is composed of an amorphous track core surrounded by an anion-deficient fluorite shell. The diameters of different track regions were estimated by using a direct impact mechanism coupled with a single overlap process to fit the transformation build-ups. These diameters depend on the sample composition, the susceptibility to amorphization by high electronic excitation increasing with the cation radius ratio r A/r B. [Copyright &y& Elsevier]

The structural transformations induced in Gd2Ti2O7 single crystals irradiated at high energies (870-MeV Xe), where ionization processes (electronic stopping) dominate, and at low energies (4-MeV Au), where ballistic processes (nuclear stopping) dominate, have been studied via the combination of Rutherford backscattering spectrometry and channeling (RB SIC), Raman spectroscopy, and transmission electron microscopy (TEM) experiments. At high energy, amorphization occurs directly in individual ion tracks from the extreme electronic-energy deposition, and full amorphization results from the overlapping of these tracks as described by a direct impact model. The track diameters lie in the range 6-9 nm. At low energy, amorphization occurs via indirect processes, driven by ballistic nuclear energy deposition from the ions, that is accounted for in the framework of both direct-impact/defect-stimulated and multi-step damage accumulation models. The ion fluence for total amorphization of the irradiated layer is much higher at low energy (0.5 ion nm-2) than at high energy (0.05 ion nm-2), consistent with the nuclear stopping at low energy (5.2 keV/nm) compared to the electronic stopping at high energy (29 keV/nm). [ABSTRACT FROM AUTHOR]

Cubic zirconia irradiated with medium-energy heavy ions exhibits a three-step damage build-up. Each step is characterized by radiation-defect reorganization that occurs to lower the system energy. The last step at high irradiation fluence is characterized by a quite unusual decrease in the damage fraction, during which the formation of defect-depleted regions is clearly evidenced. This surprising partial damage recovery is associated with a decrease in the density of tangled dislocations, which tend to form long dislocations that act as defect sinks. [Copyright &y& Elsevier]

Abstract: The damage and the residual stresses induced by 4MeV Au ion irradiation in selected ceramic oxides (cubic zirconia and Gd2(Ti2− x Zr x )O7 pyrochlores with x =1 and 2) were investigated by X-ray diffraction. The variations of the lattice parameter and of residual stresses upon irradiation were shown to depend on the compound. The highest compressive stresses, linked to the largest swelling, were found in amorphizable Gd2TiZrO7. A two-step process was observed in damage, swelling and stress build-ups for non-amorphizable oxides (zirconia and Gd2Zr2O7). [Copyright &y& Elsevier]

Abstract: Pyrochlore pellets with Gd2(Ti2− x Zr x )O7 stoichiometry were irradiated with heavy ions at energies ranging from a few MeV to a few GeV in order to compare the effects of nuclear collisions and electronic excitations. The damage created by irradiation was characterized as a function of the ion fluence by X-ray diffraction. The structural modifications induced by irradiation were shown to depend on both the sample composition and the type of irradiation. At low energy (4MeV Au ions), the susceptibility to radiation-induced amorphization exhibits a systematic decrease with increasing Zr content. At high energy (1.5GeV Xe or 2.6GeV U ions), similar structural changes are observed at much lower fluences. The lattice parameter increases for low energy irradiation, particularly in the case of amorphizable pyrochlores (Gd2Ti2O7 and Gd2TiZrO7), whereas it decreases for high energy irradiation. [Copyright &y& Elsevier]

Abstract: This article deals with the study of the micro-structural properties of cubic zirconia irradiated with swift heavy ions, based on the combination of complementary analysis techniques (TEM, AFM, XRD, RBS/C). At low irradiation fluences, cross-sectional TEM observations show the creation of latent tracks in the wake of incident ions by electronic excitation processes. The melt matter flowing from ion tracks leads to the formation of large hillocks at the surface of samples revealed by AFM. At high irradiation fluences, the overlapping of tracks results in the subdivision of crystals into slightly disoriented nano-crystallites detected by XRD. RBS/C data analyzed with a Monte-Carlo simulation code confirm the occurrence of this peculiar micro-structural transformation. [Copyright &y& Elsevier]

Abstract: The Jannus multi-ion beam facility at Saclay allows performing as well single, dual or triple beam irradiation, ion implantation and ion beam analysis. This versatility is due on one hand to the large range of ion beams available from the three coupled accelerators and on the other hand to the possibility to use several dedicated or multi-purpose vacuum chambers. It is thus possible to investigate the radiation tolerance of inorganic or organic materials and the specific effect of an atomic species of nuclear interest like hydrogen, helium, fission or transmutation products under thermal treatment or ion irradiation. This paper discusses the capabilities offered by the Jannus facility to study helium mobility in advanced nuclear materials. [Copyright &y& Elsevier]

Abstract: Yttria-stabilized cubic zirconia single-crystals have been irradiated with 4-MeV Au2+ ions at fluences ranging from 1012 cm−2 to 5×1015 cm−2 and at three temperatures (room temperature, 500°C and 800°C). Evaluation of the irradiation-induced strain has been performed by the X-ray diffraction technique. It is found that, whatever the irradiation temperature, the elastic-strain build-up exhibits two steps. An increase of the (tensile) strain-level is observed in the first step. A drastic strain relaxation occurs at a transition fluence, which defines the beginning of the second step. Increasing the irradiation temperature induces a decrease of the strain level and a shift of the transition fluence towards low fluence. Both effects may be explained by an enhanced defect-clustering rate which occurs already at 500°C. [Copyright &y& Elsevier]