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Physical properties and irradiation damage in four transition metal diborides (TM-diborides) are investigated: one high-entropy diboride (Hf0.2Nb0.2Ta0.2Ti0.2Zr0.2)B2 and three subsets of quaternary diborides. Surprisingly, instead of being generally classified as ceramic materials, the predominant mechanism for heat conduction is through electrons. The irradiation response of these TM-diborides under ion irradiation at room temperature has been investigated using 10 MeV Au ions to fluences up to 6 × 1015 Au cm−2. Black dot dislocation loops are visible at low doses, whereas dislocation networks are observed with increasing fluence. While up to ~ 4% volume expansion has been determined in these diborides, the crystalline structure remains stable under room-temperature irradiation, preserving the hexagonal AlB2 phase. Perspectives of chemical disorder resulting from various TMs in high-entropy materials, along with their associated physical properties and influence on irradiation damage, are discussed in terms of the number of valence electrons, atomic mass, and volume. [ABSTRACT FROM AUTHOR]

High entropy alloys (HEAs) are promising materials for various applications including nuclear reactor environments. Thus, understanding their behavior under irradiation and exposure to different environments is important. Here, two sets of near-equiatomic CoCrCuFeNi thin films grown on either SiO2/Si or Si substrates were irradiated at room temperature with 11.5 MeV Au ions, providing similar behavior to exposure to inert versus corrosion environments. The film grown on SiO2 had relatively minimal change up to peak damage levels above 500 dpa, while the film grown on Si began intermixing at the substrate–film interface at peak doses of 0.1 dpa before transforming into a multi-silicide film at higher doses, all at room temperature with minimal thermal diffusion. The primary mechanism is radiation-enhanced diffusion via the inverse Kirkendall and solute drag effects. The results highlight how composition and environmental exposure affect the stability of HEAs under radiation and give insights into controlling these behaviors. [ABSTRACT FROM AUTHOR]

We have studied the effect of the yttria content on the paramagnetic centers in electron-irradiated yttria-stabilized zirconia (ZrO2: Y3+) or YSZ. Single crystals with 9.5 mol % or 18 mol % Y2O3 were irradiated with electrons of 1.0, 1.5, 2.0, and 2.5 MeV. The paramagnetic center production was studied by X-band electron paramagnetic resonance (EPR) spectroscopy. The same paramagnetic centers were identified for both chemical compositions, namely two electron centers, i.e., (i) F+-type centers (involving singly ionized oxygen vacancies), and (ii) so-called T centers (Zr3+ in a trigonal symmetry site), as well as hole-centers. A strong effect is observed on the production of hole-centers that is strongly enhanced when doubling the yttria content. However, no striking effect is found on the electron centers (except the enhancement of an extra line associated with the F+-type centers). It is concluded that hole-centers are produced by inelastic interactions, whereas F+-type centers are produced by elastic collisions with no effect of the yttria content on the defect production rate. In the latter case, the threshold displacement energy (Ed) of oxygen is estimated from the electron-energy dependence of the F+-type center production rate, with no significant effect of the yttria content on Ed. An Ed value larger than 120 eV is found. This is supported by classical molecular dynamics (MD) simulations with a Buckingham-type potential that show Ed values for Y and O are likely to be in excess of 200 eV. Due to the difficulty in displacing O or Y atoms, the radiation-induced defects may alternatively be a result of Zr atom displacements for Ed = 80 ± 1 eV with subsequent defect rearrangement. [ABSTRACT FROM AUTHOR]

Depth profiles of local volume expansions are precisely measured in 6H-SiC after irradiation at 150 K with 2 MeV Pt ions and following annealing at 770 K using transmission electron microscopy equipped with electron energy loss spectroscopy. It is found that the depth profile of local volume expansion from the as-implanted sample matches well with the depth profile of irradiation-induced local disorder measured by Rutherford backscattering spectrometry. Further, the local volume expansion increases linearly with local dose up to ∼10%. By systematically comparing the depth profiles of local volume expansion and local relative disorder, it is revealed that the atomic volume of amorphous SiC continues to increase until it saturates at ∼14% due to the increased chemical short-range disorder. This is believed to be one of the reasons for significant scatter in values of volume expansion previously reported for the irradiation-induced amorphous state of SiC. [ABSTRACT FROM AUTHOR]

The defect creation at low energy events was studied using density functional theory molecular dynamics simulations in silicon carbide nanotubes, and the displacement threshold energies determined exhibit a dependence on sizes, which decrease with decreasing diameter of the nanotubes. The Stone–Wales (SW) defect, which is a common defect configurations induced through irradiation in nanotubes, has also been investigated, and the formation energies of the SW defects increase with increasing diameter of the nanotubes. The mean threshold energies were found to be 23 and 18 eV for Si and C in armchair (5,5) nanotubes. [ABSTRACT FROM AUTHOR]

SiC thermal conductivity is known to decrease under irradiation. To understand this effect, we study the variation of the thermal conductivity of cubic SiC with defect accumulation induced by displacement cascades. We use an empirical potential of the Tersoff type in the framework of nonequilibrium molecular dynamics. The conductivity of SiC is found to decrease with dose, in very good quantitative agreement with low temperature irradiation experiments. The results are analyzed in view of the amorphization states that are created by the cascade accumulation simulations. The calculated conductivity values at lower doses are close to the smallest measured values after high temperature irradiation, indicating that the decrease of the conductivity observed at lower doses is related to the creation of point defects. A subsequent decrease takes place upon further cascade accumulation. It is characteristic of the amorphization of the material and is experimentally observed for low temperature irradiation only. [ABSTRACT FROM AUTHOR]

Irradiation of pre-damaged SrTiO 3 with 2 MeV He, 1.2 MeV C, 5 MeV C and 12 MeV O ions reveals two regimes of ionization-induced recovery. For C and O ions, with electronic energy loss between 1.6 and 3 keV/nm, recovery cross-sections range from 0.27 to 0.38 nm2, and molecular dynamics confirms recovery related to ionization-induced thermal spikes via electron-phonon coupling. At lower electronic energy losses, recovery cross-sections decrease to about 5.5 × 10−4 nm2 for 2 MeV He ions and 1.0 × 10−5 nm2 for 200 keV electrons, which suggests recovery associated with local electronic excitation processes. Unlabelled Image [ABSTRACT FROM AUTHOR]

The accumulation of irradiation-induced disorder in SrTiO3 single crystals irradiated at 16 K with 200 keV Ar ions has been investigated using Rutherford backscattering spectrometry along the 〈100〉 channeling direction and compared with previous results obtained at 300 K under identical irradiation conditions. As expected, amorphization at 16 K occurs at a much lower fluence than at 300 K due to dynamic recovery of irradiation-induced defects at 300 K. Utilizing a comprehensive damage accumulation model for analysis of the data, irradiation at 16 K results only in the formation of point defects and amorphous pockets, while defect clusters are also formed at 300 K. High defect mobility under irradiation at 300 K tends to promote recombination and clustering of point defects. These results suggest that defect diffusion processes in SrTiO3 are not thermally active at 16 K. [ABSTRACT FROM AUTHOR]

Damage production and amorphization resulting from the interaction of medium-energy (from 40 to 480 keV) noble-gas ions (from He to Kr) with potassium tantalate (KTaO3) are determined using ion channeling measurements. A disorder accumulation model has been fit to the maximum damage concentration versus ion fluence to extract the cross sections for direct-impact and defect-stimulated amorphization, and the results indicate that defect-stimulated amorphization is the dominant mechanism. These cross sections exhibit a strong dependence on the calculated cross sections for displacing lattice atoms, indicating a dominant contribution of nuclear interactions to the defect production and amorphization processes under the irradiation conditions used in this study. These experimental findings, along with the model fits, suggest that the difference in recoil spectra between He and the other heavier ions may be the main driving force for the decreased damage efficiency observed for He ions, which results in a reduced rate of damage accumulation. [ABSTRACT FROM AUTHOR]

The role of dislocations on ion irradiation-induced void formation is studied in a high-entropy alloy (HEA) NiCoFeCrPd. Despite previous observations that show high-entropy alloys are swelling resistant due to a high defect recombination rate, the swelling is enhanced with increasing density of pre-existing dislocations at low strain levels that shortened transient duration before the onset of void swelling. Under certain irradiation conditions, a high density of dislocations may carry the material closer to the sink-dominated regime. Compared to another HEA NiCoFeCrMn, NiCoFeCrPd has a smaller loop size and higher loop density due to the stronger lattice distortion. Swelling behavior in a newly designed high-entropy alloy NiCoFeCrPd has been studied for the first time. Void swelling is enhanced with increasing density of pre-existing dislocations in NiCoFeCrPd. [ABSTRACT FROM AUTHOR]

Ion irradiation of KTaO3 has been performed to investigate the evolution of irradiation damage with and without significant electronic energy deposition. Damage accumulation under irradiation with 2MeV Au ions follows a direct-impact/defect-stimulated model, and occurs more rapidly than in SrTiO3 under similar conditions. Electronic energy deposition from 21 MeV Ni ions creates negligible damage in pristine KTaO3 to depths of 1 micron; however, damage is greatly enhanced in samples containing pre-existing defects, as evidenced by rapid amorphization due to track formation. The cross-sections for amorphous tracks show a nearly linear dependence on initial disorder, comparable with SrTiO3. IMPACT STATEMENT Structural modification in KTaO3 is sensitive to both electronic and nuclear energy deposition that can be controlled to exploit promising electronic and optical functionalities. [ABSTRACT FROM AUTHOR]

Recently developed concentrated solid solution alloys (CSAs) are shown to have improved performance under irradiation that depends strongly on the number of alloying elements, alloying species, and their concentrations. In contrast to conventional dilute alloys, CSAs are composed of multiple principal elements situated randomly in a simple crystalline lattice. As a result, the intrinsic disorder has a profound influence on energy dissipation pathways and defect evolution when these CSAs are subjected to energetic particle irradiation. Extraordinary irradiation resistance, including suppression of void formation by two orders of magnitude at an elevated temperature, has been achieved with increasing compositional complexity in CSAs. Unfortunately, the loss of translational invariance associated with the intrinsic chemical disorder poses great challenges to theoretical modeling at the electronic and atomic levels. Based on recent computer simulation results for a set of novel Ni-containing, face-centered cubic CSAs, we review theoretical modeling progress in handling disorder in CSAs and underscore the impact of disorder on defect dynamics. We emphasize in particular the unique challenges associated with the description of defect dynamics in CSAs. [ABSTRACT FROM AUTHOR]

Ab initio molecular dynamics simulations of low energy recoil events in wurtzite AlN have been performed to determine threshold displacement energies, defect production and evolution mechanisms, role of partial charge transfer during the process, and the influence of irradiation-induced defects on the properties of AlN. The results show that the threshold displacement energies, Ed, along the direction parallel to the basal planes are smaller than those perpendicular to the basal planes. The minimum Ed values are determined to be 19 eV and 55 eV for N and Al atom, respectively, which occur along the [ 1 ¯ 1 ¯ 20 ] direction. In general, the threshold displacement energies for N are smaller than those for Al atom, indicating the N defects would be dominant under irradiation. The defect production mechanisms have been analyzed. It is found that charge transfer and redistribution for both the primary knock-on atom and the subsequent recoil atoms play a significant role in defect production and evolution. Similar to the trend in oxide materials, there is a nearly linear relationship between Ed and the total amount of charge transfer at the potential energy peak in AlN, which provides guidance on the development of charge-transfer interatomic potentials for classic molecular dynamics simulations. Finally, the response behavior of AlN to low energy irradiation is qualitatively investigated. The existence of irradiation-induced defects significantly modifies the electronic structure, and thus affects the magnetic, electronic and optical properties of AlN. These findings further enrich the understanding of defects in the wide bandgap semiconductor of AlN. [ABSTRACT FROM AUTHOR]

Thin films of nanocrystalline ceria deposited onto a silicon substrate have been irradiated with 3 MeV Au+ ions to a total dose of 34 displacements per atom to examine the film/substrate interfacial response upon displacement damage. Under irradiation, a band of contrast is observed to form that grows under further irradiation. Scanning and high-resolution transmission electron microscopy imaging and analysis suggest that this band of contrast is a cerium silicate phase with an approximate Ce: Si: O composition ratio of 1:1:3 in an amorphous nature. The slightly nonstoichiometric composition arises due to the loss of mobile oxygen within the cerium silicate phase under the current irradiation condition. This nonequilibrium phase is formed as a direct result of ion-beam-induced chemical mixing caused by ballistic collisions between the incoming ion and the lattice atoms. This may hold promise in ion beam engineering of cerium silicates for microelectronic applications e.g., the fabrication of blue LEDs. [ABSTRACT FROM AUTHOR]

Previous computer simulations of multiple 10 keV Si cascades in 3C-SiC demonstrated that many damage-state properties exhibit relatively smooth, but noticeably different, dose dependencies. A more recent analysis of these damage-state properties, which includes additional data at low and intermediate doses, reveals more complex relationships between system energy, swelling, energy per defect, relative disorder, elastic modulus, and elastic constant, C11. These relationships provide evidence for the onset of both defect clustering and solid-state amorphization, which appear to be driven by local energy and elastic instabilities from the accumulation of defects. The results provide guidance on experimental approaches to reveal the onset of these processes. [ABSTRACT FROM AUTHOR]

Abstract: Response of materials to single radiation events is fundamental to research and many technological applications that involve energetic particles. Ion–solid interactions lead to energy loss of ions, production of electron–hole pairs, and light emission from excitation-induced luminescence. Employing a unique time-of-flight system, material response to single ion irradiation has been utilized to measure electronic energy loss, and to evaluate materials performance for radiation detection. Measurements of electronic energy loss of single ions in a thin ZrO2 foil over a continuous energy range exhibit good agreement with SRIM predictions for He and Be ions. For O and F ions, slight over- and under-estimation of SRIM prediction is evident at energies around 250 (near the stopping maximum) and above 800keV/nucleon, respectively. For a Si semiconductor detector, its response to single ion irradiation shows that pulse height defect is clear for elements heavier than Si, and nonlinear energy response is significant for all elements at energies below ∼100keV/nucleon. For a single crystal CsI:Tl scintillator, the response to H ion events is used to determine relative light yield and absolute energy resolution over a wide energy region, where energy resolution of ∼5.3% is achieved at 2MeV. [Copyright &y& Elsevier]

Abstract: Irradiation-induced amorphization in 6H-SiC has been previously studied as a function of irradiation temperature for electrons and ions ranging from Ne to Au. Analysis of these data with a dynamic model for amorphization reveals that the amorphization dose increases and the critical amorphization temperature decreases as the ratio of in-cascade ionization to displacement rates increases. Model fits to the data yield the ratio of radiation-induced recovery cross section, σ r, to damage cross section, σ d, and an activation energy of 0.12±0.01eV for irradiation-induced recovery. The critical temperature exhibits a linear dependence on 1/ln(σ r/σ d), consistent with the model. [Copyright &y& Elsevier]

The article presents a study addressing ion beam irradiation versus quenching from a melt. Study shows a substantial evidence which indicates differences between the two types of aperiodic state such as the spectral and structural differences. It is noted that while IR-reflection technique is used, infrared spectroscopy has also shown to be useful in distinguishing differences between the crystalline and aperiodic structures.

The authors have investigated the effects of 200 and 300 keV electron-beam irradiations on amorphization in 6H-SiC at 100 and 295 K. Amorphization is induced by the accumulation of defects produced by direct atomic displacements. Dynamic recovery of these defects during irradiation, due to temperature increases and ionization effects, results in increases in the amorphization dose. By comparing with previous data for 2 MeV electrons and 1.5 MeV Xe ions, the results demonstrate that ionization-enhanced recovery in 6H-SiC dramatically increases above an ionization rate threshold. [ABSTRACT FROM AUTHOR]

Electron-beam induced recrystallization of irradiation-induced amorphous Sr2Nd8(SiO4)6O2 is investigated in situ using transmission electron microscopy with 200 keV electrons at room temperature. Epitaxial recrystallization is observed from both the amorphous/crystalline interface and the surface, and the recrystallization is more pronounced with increasing electron-beam flux. Since the temperature increase induced by electron-beam irradiation is estimated to be less than 7 K and maximum energies transferred to target atoms are below the displacement energies, ionization-induced processes are considered to be the primary mechanisms for the solid-phase epitaxial recrystallization observed in the present study. [ABSTRACT FROM AUTHOR]

We use the two-temperature model in molecular dynamic simulations of 150 keV Ni ion cascades in nickel and nickel-based alloys to investigate the effect of the energy exchange between the atomic and the electronic systems during the primary stages of radiation damage. We find that the electron-phonon interactions result in a smaller amount of defects and affect the cluster formation, resulting in smaller clusters. These results indicate that ignoring the local heating due to the electrons results in the overestimation of the amount of damage and the size of the defect clusters. A comparison of the average defect production to the Norgett-Robinson-Torrens (NRT) prediction over a range of energies is provided. [ABSTRACT FROM AUTHOR]

The structure and ion-conducting properties of the defect-fluorite ring structure formed around amorphous ion-tracks by swift heavy ion irradiation of Gd2Ti2O7 pyrochlore are investigated. High angle annular dark field imaging complemented with ion-track molecular dynamics simulations show that the atoms in the ring structure are disordered, and have relatively larger cation-cation interspacing than in the bulk pyrochlore, illustrating the presence of tensile strain in the ring region. Density functional theory calculations show that the non-equilibrium defect-fluorite structure can be stabilized by tensile strain. The pyrochlore to defect-fluorite structure transformation in the ring region is predicted to be induced by recrystallization during a melt-quench process and stabilized by tensile strain. Static pair-potential calculations show that planar tensile strain lowers oxygen vacancy migration barriers in pyrochlores, in agreement with recent studies on fluorite and perovskite materials. In view of these results, it is suggested that strain engineering could be simultaneously used to stabilize the defect-fluorite structure and gain control over its high ion-conducting properties. [ABSTRACT FROM AUTHOR]

The accumulation of irradiation-induced disorder in single crystal CeO 2 has been investigated over a wide range of ion fluences. Room temperature irradiations of epitaxial CeO 2 thin films using 2 MeV Au 2+ ions were carried out up to a total fluence of 1.3 × 10 16 cm −2 Post-irradiation disorder was characterized using ion channeling Rutherford backscattering spectrometry (RBS/C) and confocal Raman spectroscopy. The Raman measurements were interpreted by means of a phonon confinement model, which employed rigid ion calculations to determine the phonon correlation length in the irradiated material. Comparison between the dose dependent changes in correlation length of the Raman measurements and the Ce disorder fraction from RBS/C provides complementary quantitative details on the rate of point and extended defect formation on the Ce and O sub-lattices over a broad range of ion fluences. Raman measurements, which are significantly more sensitive than RBS/C at low doses, reveal that the nucleation rate of defects is highest below 0.1 displacements per atom (dpa). Comparison between Raman and RBS/C measurements suggests that between 0.1 and 10 dpa the damage evolution is characterized by modest growth of point defects and/or small clusters, while above 10 dpa the preexisting defects rapidly grow into extended clusters and/or loops. [ABSTRACT FROM AUTHOR]

Using molecular dynamics simulations and the two-temperature model, we provide a comparison of the surviving damage from single ion irradiation events in nickel-based alloys, for cascades with and without taking into account the effects of the electronic excitations. We find that including the electronic effects impacts the amount of the resulting damage and the production of isolated defects. Irradiation of nickel–palladium systems results in larger numbers of defects compared to nickel–iron systems, with similar numbers of isolated defects. We additionally investigate the mass effect on the two-temperature model in molecular dynamics simulations of cascades. [ABSTRACT FROM AUTHOR]

Electron-beam-induced effects in preamorphized Sr2Nd8(SiO4)6O2 were investigated in situ using transmission electron microscopy with 200-keV electrons at temperatures ranging from 380 to 780 K. Within the electron-irradiated area, epitaxial recrystallization was observed from the amorphous/crystalline interface toward the surface, with the rate of recrystallization increasing as temperature increased from 380 to 580 K. Structural contrast features (i.e., O deficient amorphous material), as well as recrystallization, were observed outside of the irradiation area at temperatures from 680 to 780 K. Ionization-induced processes and local nonstoichiometry induced by oxygen migration and desorption are possible mechanisms for the electron-beam- induced recrystallization and for the formation of the structural contrast features, respectively. [ABSTRACT FROM AUTHOR]

Grain growth issues in nanocrystalline ceramic oxides render their highly attractive properties practically unusable due to limited understanding of the underlying grain-growth mechanisms. Two conventional “slow” grain-growth mechanisms, i.e. curvature driven and grain-rotation driven, are shown to be thermally active, and the discovery of a “fast” disorder-driven mechanism is revealed using molecular dynamics simulation on nanocrystalline ceria, in conjunction with experimental observations. We show that this disorder mechanism drives the unexpected fast grain growth observed experimentally during synthesis and irradiation conditions. [ABSTRACT FROM AUTHOR]

Abstract: Recent demands for new radiation detector materials with improved γ-ray detection performance at room temperature have prompted research efforts on both accelerated material discovery and efficient techniques that can be used to identify material properties relevant to detector performance. New material discovery has been limited due to the difficulties of large crystal growth to completely absorb γ-energies; whereas high-quality thin films or small crystals of candidate materials can be readily produced by various modern growth techniques. In this work, an ion-scintillator technique is demonstrated that can be applied to study scintillation properties of thin films and small crystals. The scintillation response of a benchmark scintillator, europium-doped calcium fluoride (CaF2:Eu), to energetic proton and helium ions is studied using the ion-scintillator approach based on a time-of-flight (TOF) telescope. Excellent energy resolution and fast response of the TOF telescope allow quantitative measurement of light yield, nonlinearity and energy resolution over an energy range from a few tens to a few thousands of keV. [Copyright &y& Elsevier]

High entropy ceramics (HECs) are a novel class of ceramics that exhibit high melting point, excellent high-temperature mechanical performance, and superb corrosion resistance, making them promising candidates for advanced nuclear reactors. Notably, encouraging irradiation tolerance has been found in a few HECs based on the scattered reports in the current literature. In this article, we systematically review the recent progress in the irradiation response of HECs, including high entropy carbides, high entropy pyrochlore oxides, high entropy MAX phases, and high entropy nitride films. The influence of chemical complexity on the irradiation properties of HECs is examined by comparing them with their corresponding single-component ceramic counterparts. Besides, the similarities and differences between HECs and widely-studied high entropy alloys are discussed regarding their irradiation responses. In the end, we envisage prospects for the future development of irradiation-tolerant HECs. [ABSTRACT FROM AUTHOR]

To better understand defect structure and the evolution of irradiation-induced damage in single crystal Ni, in situ Rutherford backscattering spectroscopy in channeling geometry (RBS/C) is performed along the <100>, <110>, and <211> axes with different probing beam energies. The RBS/C data reveal that damage evolution occurs in three steps. The first step at low doses (up to 0.2 dpa), characterized by a linear increase with dose, is related to the formation of point defects and small clusters. The second step in the intermediate dose range (0.2–1.0 dpa) shows a sublinear increase in disorder to saturation. This sublinear increase is due to the growth of defect clusters resulting from the interaction of irradiation-induced defects with already existing damage from previous ion impacts. The third step at high doses (1.0–32.4 dpa) exhibits a surprising decrease in the disorder level, which may be attributed to defect evolution from black spot defects to large dislocation loops that leads to strain relaxation. In addition, the damage extends much deeper than the predicted depths and is attributed to long-range defect migration effects confirmed by transmission electron microscopy (TEM) observations. Although similar damage evolution trends have been observed along all channeling directions, the disorder accumulation is largest along the <100> and <211> axes than observed along <110> axis. This "preferential" disordering process along <100> and <211> suggests that more defects are shielded by the <110> atomic rows than the two other axes. The co-existence of both uncorrelated displaced lattice atoms and dislocation loops in Ni irradiated at 1 ion/nm2 is revealed by the energy-dependent RBS/C studies along all three axes. In contrast, dislocation loops and stacking fault tetrahedral are simultaneously present in the crystal structure of Ni irradiated at 100 ions/nm2 that is consistent with previous molecular dynamics simulations and TEM observations. Image 1 • RBS/C show that disordering kinetics exhibit three different regions of defect formation along all the axes studied. • Both uncorrelated displaced lattice atoms and dislocation loops co-exist in Ni irradiated at low doses. • Dislocation loops and SFT are simultaneously present in the crystal structure of Ni irradiated at high doses. • Additional information on the nature of defects can be obtained using multi-axial and multi-energy ion channeling analysis. [ABSTRACT FROM AUTHOR]

Medium entropy alloy NiCoCr draws great attention due to its excellent strength-ductility trade-off mechanical behavior. Its irradiation behavior at elevated temperatures has been investigated using ion beam irradiation in a temperature range of 420–580°Cand transmission electron microscopy. Irradiation induced stacking fault tetrahedra were only observed at 420 °C. With increasing irradiation temperature, all stacking fault tetrahedra vanished, while the size of voids and dislocation loops increased significantly. Nanoindentation-induced structural complexities, including dislocations, stacking faults and twins helped to reduce void swelling. However, at the elevated temperatures, NiCoCr is still much more susceptible to void swelling compared to high entropy alloys such as NiCoFeCrMn and NiCoFeCrPd. Image 1 [ABSTRACT FROM AUTHOR]

The evolution of radiation-induced defects in Ni and the single-phase concentrated solid solution alloy, NiCoCr, were investigated during in situ 2.8 MeV Au ion irradiation and post-irradiation analysis using transmission electron microscopy. Compared to Ni, both the size and area density of defect clusters decreased in NiCoCr under the same irradiation conditions, suggesting that the chemical complexity, i.e., randomness of lattice site occupations, of NiCoCr suppressed radiation-induced damage. One-dimensional glide of defect clusters was observed in Ni but not in the NiCoCr alloy. The structural nature of small defect clusters in NiCoCr were further investigated using high-angle annular dark field scanning transmission electron microscopy. • Smaller and fewer defects were generated in more chemically-complicated alloys. • One-dimensional gild of defect clusters was observed in Ni but not in NiCoCr. • Both vacancy-type and interstitial-type defect clusters were identified in NiCoCr. [ABSTRACT FROM AUTHOR]

Damage production and amorphization resulting from the interaction of medium-energy (from 40 to 480 keV) noble-gas ions (from He to Kr) with potassium tantalate (KTaO3) are determined using ion channeling measurements. A disorder accumulation model has been fit to the maximum damage concentration versus ion fluence to extract the cross sections for direct-impact and defect-stimulated amorphization, and the results indicate that defect-stimulated amorphization is the dominant mechanism. These cross sections exhibit a strong dependence on the calculated cross sections for displacing lattice atoms, indicating a dominant contribution of nuclear interactions to the defect production and amorphization processes under the irradiation conditions used in this study. These experimental findings, along with the model fits, suggest that the difference in recoil spectra between He and the other heavier ions may be the main driving force for the decreased damage efficiency observed for He ions, which results in a reduced rate of damage accumulation. [ABSTRACT FROM AUTHOR]

One of the biggest challenges in the radiation induced defect science is to understand the complex nature of ion-atom interactions under highly extreme conditions. Here, we report the irradiation induced non-equilibrium defect formation in NiCoCr single phase concentrated solid solution alloy due to (i) the extreme inelastic and (ii) the coupled inelastic and elastic ion-atom interactions. These two conditions are achieved at 5 and 30 μm penetration depths along the paths of swift heavy ions (1.542 GeV Bi). In general, the irradiation induced damage consists of interstitial-type dislocation loops and vacancy-type stacking fault tetrahedra (SFT). Near the surface (~5 μm) where electronic energy loss is dominating (~62.5 keV nm −1 ), the atomic motion primarily results in the formation of SFT. A noticeable increase of dislocation loop formation is observed at 30 μm near the maximum energy deposition from elastic interactions (~4.9 keV nm −1 ), as compared to the near surface region (~0.06 keV nm −1 ). Insights on the complex electronic and atomic correlations of extreme energy deposition and dissipation on defect dynamics and structural stability may pave the way for new design principles of radiation–tolerant structural alloys. [ABSTRACT FROM AUTHOR]

The lack of fundamental understanding on the coupled effects of energy deposition to electrons and atomic nuclei on defect processes and irradiation response poses a significant roadblock for the design and control of material properties. In this work, SrTiO 3 has been irradiated with various ion species over a wide range of ion fluences at room temperature with a goal to deposit different amounts of energy to target electrons and atomic nuclei by varying the ratio of electronic to nuclear energy loss. The results unambiguously show a dramatic difference in behavior of SrTiO 3 irradiated with light ions (Ne, O) compared to heavy ions (Ar). While the damage accumulation and amorphization under Ar ion irradiation are consistent with previous observations and existing models, the damage accumulation under Ne irradiation reveals a quasi-saturation state at a fractional disorder of 0.54 at the damage peak for an ion fluence corresponding to a dose of 0.5 dpa; this is followed by further increases in disorder with increasing ion fluence. In the case of O ion irradiation, the damage accumulation at the damage peak closely follows that for Ne ion irradiation up to a fluence corresponding to a dose of 0.5 dpa, where a quasi-saturation of fractional disorder level occurs at about 0.48; however, in this case, the disorder at the damage peak decreases slightly with further increases in fluence. This behavior is associated with changes in kinetics due to irradiation-enhanced diffusional processes that are dependent on electronic energy loss and the ratio of electronic to nuclear energy dissipation. These findings are critical for advancing the fundamental understanding of ion-solid interactions and for a large number of applications in oxide electronics where SrTiO 3 is a foundational material. [ABSTRACT FROM AUTHOR]

Understanding energy dissipation processes in electronic/atomic subsystems and subsequent non-equilibrium defect evolution is a long-standing challenge in materials science. In the intermediate energy regime, energetic particles simultaneously deposit a significant amount of energy to both electronic and atomic subsystems of silicon carbide (SiC). Here we show that defect evolution in SiC closely depends on the electronic-to-nuclear energy loss ratio ( S e / S n ), nuclear stopping powers ( dE / dx nucl ), electronic stopping powers ( dE / dx ele ), and the temporal and spatial coupling of electronic and atomic subsystem for energy dissipation. The integrated experiments and simulations reveal that: (1) increasing S e / S n slows damage accumulation; (2) the transient temperatures during the ionization-induced thermal spike increase with dE / dx ele , which causes efficient damage annealing along the ion trajectory; and (3) for more condensed displacement damage within the thermal spike, damage production is suppressed due to the coupled electronic and atomic dynamics. Ionization effects are expected to be more significant in materials with covalent/ionic bonding involving predominantly well-localized electrons. Insights into the complex electronic and atomic correlations may pave the way to better control and predict SiC response to extreme energy deposition. [ABSTRACT FROM AUTHOR]

The evolution of irradiation-induced atomic strain in an equiatomic NiFe concentrated solid-solution alloy is investigated using both atomistic simulations and x-ray diffraction analysis. The irradiations are performed using 1.5 MeV Ni ions to fluences ranging from 1 × 10 13 to 1 × 10 14 cm − 2 . The irradiation simulations are carried out by overlapping 5 keV Ni recoils cascades up to a total of 300 recoils. An increase of volumetric strain is observed at low dose, which is associated with production of point defects and small clusters. Relaxation of strain occurs at higher doses, when large defect clusters, e.g., dislocation loops, dominate. [ABSTRACT FROM AUTHOR]

Using molecular dynamics simulations, we elucidate irradiation-induced point defect evolution in fcc pure Ni, Ni 0.5 Fe 0.5 , and Ni 0.8 Cr 0.2 solid solution alloys. We find that irradiation-induced interstitials form dislocation loops that are of 1/3〈1 1 1〉{1 1 1}-type, consistent with our experimental results. While the loops are formed in all the three materials, the kinetics of formation is considerably slower in NiFe and NiCr than in pure Ni, indicating that defect migration barriers and extended defect formation energies could be higher in the alloys than pure Ni. As a result, while larger size clusters are formed in pure Ni, smaller and more clusters are observed in the alloys. Vacancy diffusion occurs at relatively higher temperatures than interstitials, and their clustering leads to the formation of stacking fault tetrahedra, consistent with our experiments. The results also show that the surviving Frenkel pairs are composition dependent and are largely Ni dominated. [ABSTRACT FROM AUTHOR]