Structural, mechanical, and dimensional evolutions of silicon carbide (SiC) induced by heavy-ion irradiations are studied by means of Rutherford backscattering spectrometry and channeling (RBS/C), nanoindentation, and surface profilometry measurements. $4H$ - and $6H\text{-SiC}$ single crystals were irradiated with 4 MeV ${\text{Au}}^{2+}$ and 4 MeV ${\text{Xe}}^{+}$ ions at room temperature (RT) or $400°\text{C}$ . Using a Monte Carlo program to simulate the RBS/C spectra (MCCHASY code), we find that Au ion irradiation at RT induces a total silicon sublattice disorder related to full amorphization at a dose of about 0.4 displacement per atom (dpa). A two-step damage process is found on the basis of the disordered fractions deduced from RBS/C data. Complete amorphization cannot be reached upon both Au and Xe ion irradiations at $400°\text{C}$ up to about 26 dpa because of the dynamic annealing of defects. When complete amorphization is reached at RT, the Young’s modulus and Berkovich hardness of irradiated $6H\text{-SiC}$ samples are lower by, respectively, 40% and 45% than those of the virgin crystals. The out-of-plane expansion measured by surface profilometry increases versus irradiation dose and the saturation value measured in the completely amorphous layer (normalized to the ion projected range) is close to 25%. We show that the modifications of the macroscopic properties are mainly due to the amorphization of the material. The macroscopic elasticity constants and dimensional properties are predicted for a composite material made of crystalline matrix containing dispersed amorphous inclusions using simple analytical homogenization models. Voigt’s model seems to give the best approximation for disordered fractions larger than 20% in the second step of the damage process.

Yttria-stabilized zirconia single crystals were irradiated with a variety of different swift heavy ions (from $145\mathrm{MeV}$ C to $2.6\mathrm{GeV}$ U) in a broad fluence range (between ${10}^{11}$ and ${10}^{15}{\mathrm{cm}}^{-2}$ ). Surface profilometry measurements show that the out-of-plane expansion of the samples increases versus ion fluence up to an asymptotic value of about 0.2%; the larger the ion mass, the smaller the fluence needed to reach saturation. Rutherford backscattering spectrometry data on irradiated crystals under channeling conditions give clear evidence of lattice damage creation for ions heavier than Br corresponding to a threshold electronic stopping power about $20\mathrm{keV}{\mathrm{nm}}^{-1}$ . In contrast, no threshold is found for the swelling data which scale fairly well with the number of displacements per atom (except for the irradiation with U ions). In all cases we find a linear increase of the out-of-plane expansion versus the concentration of $F^{+}$ -type centers (singly ionized oxygen vacancies) measured by electron paramagnetic resonance spectroscopy in as-received and thermochemically reduced samples, regardless of crystal orientation. The nature of the lattice disorder and the respective effects of elastic collisions and electronic excitations on the ion-induced volume expansion and damage are discussed.

This paper highlights the use and applications of the energy loss function (ELF) for materials analysis by using electron energy loss spectroscopy (EELS). The basic Drude–Lindhart theory of the ELF is briefly presented along with reference to reflection electron energy loss (REELS) data for several dielectric materials such as insulating high-k binary oxides and semiconductors. Those data and their use are critically discussed. A comparison is made to the available ab initio calculations of the ELF for these materials. Experimental, high-resolution TEM-EELS data on Si, SiC, and CeO₂ obtained using a high-resolution, double-Cs-corrected transmission electron microscope are confronted to calculated spectra on the basis of the ELF theory. Values of plasmon energies of these three dielectric materials are quantitatively analyzed on the basis of the simple Drude’s free electron theory. The effects of heavy ion irradiation on the TEM-EELS spectra of Si and SiC are addressed. In particular, the downward shifts of plasmon peaks induced by radiation damage and the subsequent amorphization of Si and SiC are discussed. TEM-EELS data of CeO₂ are also analyzed with respect to the ELF data and with comparison to isostructural ZrO₂ and PuO₂ by using the same background and with reference to ab initio calculations.

Single crystals of magnesium aluminate spinel (MgAl ₂ O ₄ ) with (1 0 0) or (1 1 0) orientations and cerium dioxide or ceria (CeO ₂ ) were irradiated by 1.0 MeV and 2.5 MeV electrons in a high-fluence range. Point-defect production was studied by off-line UV–visible optical spectroscopy after irradiation. For spinel, regardless of both crystal orientation and electron energy, two characteristic broad bands centered at photon energies of 5.4 eV and 4.9 eV were assigned to F and F ⁺ centers (neutral and singly ionized oxygen vacancies), respectively, on the basis of available literature data. No clear differences in color-center formation were observed for the two crystal orientations. Using calculations from displacement cross sections by elastic collisions, these results are consistent with a very large threshold displacement energy (200 eV) for oxygen atoms at room temperature. A third very broad band centered at 3.7 eV might be attributed either to an oxygen hole center (V-type center) or an F ₂ dimer center (oxygen di-vacancy). The onset of recovery of these color centers took place at 200 °C with almost full bleaching at 600 °C. Activation energies (~0.3–0.4 eV) for defect recovery were deduced from the isochronal annealing data by using a first-order kinetics analysis. For ceria, a sub-band-gap absorption feature, which peaked at ~3.1 eV, was recorded for 2.5 MeV electron irradiation only. Assuming a ballistic process, we suggest that the latter defect might result from cerium atom displacement on the basis of computed cross sections.

Pure and (Ca and Si)-substituted yttrium iron garnet (Y ₃ Fe ₅ O ₁₂ or YIG) epitaxial layers and amorphous films on gadolinium gallium garnet (Gd ₃ Ga ₅ O ₁₂ , or GGG) single crystal substrates were irradiated by 50 MeV ³² Si and 50 MeV (or 60 MeV) ⁶³ Cu ions for electronic stopping powers larger than the threshold value (~4 MeV μ m ⁻¹ ) for amorphous track formation in YIG crystals. Conductivity data of crystalline samples in a broad ion fluence range (10 ¹¹ –10 ¹⁶ cm ⁻² ) are modeled with a set of rate equations corresponding to the amorphization and recrystallization induced in ion tracks by electronic excitations. The data for amorphous layers confirm that a recrystallization process takes place above ~10 ¹⁴ cm ⁻² . Cross sections for both processes deduced from this analysis are discussed in comparison to previous determinations with reference to the inelastic thermal-spike model of track formation. Micro-Raman spectroscopy was also used to follow the related structural modifications. Raman spectra show the progressive vanishing and randomization of crystal phonon modes in relation to the ion-induced damage. For crystalline samples irradiated at high fluences (⩾10 ¹⁴ cm ⁻² ), only two prominent broad bands remain like for amorphous films, thereby reflecting the phonon density of states of the disordered solid, regardless of samples and irradiation conditions. The main band peaked at ~660 cm ⁻¹ is assigned to vibration modes of randomized bonds in tetrahedral (FeO ₄ ) units.