This paper presents the technical details and commissioning results of a newly upgraded platform for ion-irradiation experiments under multi-GPa static pressure conditions at the GSI Helmholtz Center for Heavy Ion Research (Darmstadt, Germany), now accessible to external users. The GSI SIS18 accelerator provides heavy ions with tens of GeV kinetic energies, capable of penetrating through diamond anvil cells and depositing extremely high energy densities within the pressurized samples. This energy deposition triggers ultrafast, localized structural and phase transformations at the nanoscale. The platform integrates online optical microscopy and Raman spectroscopy, providing real-time monitoring of material modifications during stepwise fluence accumulation. By enabling controlled studies of structural responses and phase transitions under coupled extreme conditions, this setup opens unprecedented opportunities for research across condensed-matter physics, materials science, geoscience, high-pressure chemistry, and planetary science.

The ionoluminescence response of the ultraviolet emission bands in wurtzite GaN was investigated in situ under 1.75 MeV O2+ irradiation from 68 to 200 K. A systematic decrease in luminescence intensity with increasing ion fluence was observed, evidencing the formation of non-radiative recombination centers. The quenching behavior exhibits a pronounced temperature dependence, reflecting the complex competition between defect formation, migration, and recovery processes. Arrhenius analysis of thermal quenching at the onset of irradiation revealed an activation energy of 105 meV for the dominant non-radiative process. The beam-induced cross sections associated with non-radiative recombination were obtained by fitting an analytical model to the ion fluence dependent yield curves. The cross sections were found to increase as temperature is reduced, indicating enhanced efficiency of the non-radiative channel when defect mobility and/or dynamic annealing are suppressed. This study provides insights into the role that radiation-induced structural defects may play on electronic transport properties in GaN-based devices used in low temperature radiation environments, such as those found in satellites and spacecraft.

The high-entropy perovskite Eu(Sc/Cr/Fe/Ni/Al)O3 was investigated to explore its multifunctionality and correlated behavior. Special Quasirandom Structure (SQS)-based X-ray Pair Distribution Function (PDF) analysis reveals anomalously short Eu-Ni and long Ni–O distances, explained by an electrostatic leaning of Ni cations toward Eu at the ground state with bond-valence analysis predicting the coexistence of Ni2+, Cr3+ and Cr4+. Temperature-dependent X-ray diffraction analysis reveals continuous unit-cell contraction upon cooling, with anomalous features near 140 K, accompanied by peak broadening—indicating structural change. AC phase-angle features suggest changes in the dielectric constants at 260 K and 140 K, indicating polaronic transport. The derivative heat capacity below 130 K, likely associated with ordering of the disproportionated magnetic sublattices. Photoluminescence spectra reveal marked intensity quenching below 150 K, possibly-due to the suppression of Cr3+ emission. These results cumulatively suggest a cooperative charge ordering or disproportionation below 140 K.

The electronic energy loss spectra of ceria (CeO2) irradiated with swift heavy ions (27 MeV Xe and 946 MeV Au) in the electronic slowing down regime were measured for bulk sintered samples and nanoparticles by using a double Cs-corrected transmission electron microscope. The low-loss region as well as the core-loss region, including the oxygen K-edge and cerium M-4,M- 5 white lines, were recorded. No strong lattice disorder was found in the low-loss peaks for both types of samples showing the same bulk oxygen plasmon loss peak at about 15 eV. However, there is a clear evidence of cerium reduction to the trivalent oxidation state after irradiation for the sintered samples as shown by the K-edge shape of oxygen and decrease of the Ce M-4/M-5 intensity ratio. A similar change of the M-4/M-5 intensity ratio was observed for the irradiated nanoparticles with respect to the virgin sample owing to the high energy input inside the nanograin. The effect of radiation damage on electron energy loss spectroscopy data is analyzed for both types of samples and irradiation conditions.

Radiation hardness is a critical requirement for gallium nitride (GaN)-based devices operating in space and radiation intensive environments. We investigate irradiation induced microstructure and strain evolution in multilayer GaN heterostructures exposed to 950 MeV Au-197 swift heavy ions (SHI) at fluences of 1 & times; 10(12) and 8 & times; 10(12) ions cm(-2), for which the electronic stopping power in GaN (similar to 44.5 keV/nm) substantially exceeds the reported track-formation threshold (similar to 17 keV/nm). Combining high-resolution X-ray diffraction (HRXRD), cross-sectional transmission electron microscopy (TEM), and molecular dynamics (MD) simulations, we find an anisotropic lattice distortion that intensifies with fluence, reaching +1.25% tensile strain along the c-axis and - 1.55% compressive strain along the a-axis. The measured c-axis strain exceeds the purely elastic prediction, indicating defect mediated strain accommodation consistent with an ion-hammering response. Diffraction peak broadening and diffuse scattering indicate reduced crystalline coherence length and increased mosaicity. TEM confirms nanoscale cavities aligned along ion trajectories throughout the GaN layer, with the average cavity diameter increasing from 1.6 to 2.1 nm and the corresponding swelling from 0.23% to 0.33% at the higher fluence. MD simulations reproduce the measured strain anisotropy and indicate enhanced cavity growth from overlapping ion tracks at higher fluence. These results provide a correlated experimental-computational picture of how SHI irradiation modifies the lattice response and defect landscape in epitaxial GaN, offering mechanistic insight relevant to the radiation tolerance of GaN based devices.

Hyperstoichiometric UO2.15 was characterized by neutron total scattering at high temperature in the single-phase UO2+x region of the U/O phase diagram. The diffraction data confirmed a single-phase fluorite structure at high temperature. Analysis of the short-range data showed that the same structural model does not fit the pair distribution functions well. Instead, structural models containing specific configurations of oxygen defect clusters best represent the local atomic arrangement. Prevalent defect clusters previously proposed were fit to the experimental data, and moderately distorted oxygen cuboctahedra hypothesized by recent molecular dynamics simulations fit the data most accurately.

Metastable phases can exist within local minima in the potential energy landscape when they are kinetically "trapped" by various processing routes, such as thermal treatment, grain size reduction, chemical doping, interfacial stress, or irradiation. Despite the importance of metastable materials for many technological applications, little is known about the underlying structural mechanisms of the stabilization process and atomic-scale nature of the resulting defective metastable phase. Investigating ion-irradiated and nanocrystalline zirconia with neutron total scattering experiments, we show that metastable tetragonal ZrO2 consists of an underlying structure of ferroelastic, orthorhombic nanoscale domains stabilized by a network of domain walls. The apparent long-range tetragonal structure that can be recovered to ambient conditions is only the configurational ensemble average of the underlying orthorhombic domains. This structural heterogeneity with a distinct short-range order is more broadly applicable to other nonequilibrium materials and provides insight into the synthesis and recovery of functional metastable phases with unique physical and chemical properties.

Compositionally complex oxides have garnered attention recently for their potential technological applications in harsh environments such as thermal barrier coatings and nuclear waste forms. Therefore, their response to extreme conditions, including high temperature and intense irradiation fields, must be thoroughly investigated. Here, the structural evolution of two pyrochlore oxides with comparable cation size ratio, rA/rB, (Yb0.2Er0.2Dy0.2Tb0.2Gd0.2)2Ti2O7 and Ho2Ti2O7, was evaluated after irradiation with 946 MeV Au ions up to a fluence of 8 × 1012 ions/cm2 using synchrotron X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. The overall radiation response is comparable for both titanate oxides and is dominated by a loss of crystallinity. When compared to a series of conventional titanate pyrochlore compositions, the amorphous track diameter of (Yb0.2Er0.2Dy0.2Tb0.2Gd0.2)2Ti2O7 is slightly larger than that of Ho2Ti2O7 and more in line with the diameter of the endmember with the maximum A-site cation size (Gd2Ti2O7). Density functional theory calculations suggest that this behavior may be linked to local lattice distortions and the associated energetics of cation antisite formation. TEM and Raman analyses show that a disordered, crystalline shell surrounds the amorphous ion tracks in (Yb0.2Er0.2Dy0.2Tb0.2Gd0.2)2Ti2O7, and the corresponding short-range structure resembles a weberite-type atomic arrangement.

The radiation hardness of GaN-based devices is a critical metric for applications in extreme environments. This study investigates the structural changes in GaN and AlN induced by swift heavy ion (SHI) irradiation, characteristic of space radiation environments. A multilayered GaN/AlN structure is exposed to 950 MeV Au ions at fluences of 1×1012 and 8×1012 ions/cm2. Subsequent post-irradiation characterization, including transmission electron microscopy and energy-dispersive x-ray spectroscopy, reveal no apparent amorphization across the entire sample. Notably, significant nanometer-sized cavities are observed in both GaN and AlN. The cavities in GaN exhibit an increase in number density and diameter with increasing SHI irradiation, with the average diameter progressing from 1.80 to 2.10 nm. In contrast, cavities in AlN appear considerably smaller. Molecular dynamics simulations, coupled with the inelastic thermal spike model, reproduce the presence of cavities in GaN and no cavities in the AlN structure. This difference is attributed to the faster heat dissipation and stronger bonding in AlN. Considering the overlapping of ion impacts at high fluences, simulations confirm the enlargement of cavity size in GaN. These findings contribute to a mechanistic understanding of the contrast in ion–matter interactions and induced microstructures between AlN and GaN under extreme ionizing radiation conditions. This disparity could potentially impact electronic performance through the formation of defect traps and interfacial strain fields.

Reidite, a high-pressure phase of zircon, is increasingly identified at terrestrial impact sites. Despite its growing recognition, the potential applications for estimating minimum impact pressure face impediments due to existing discrepancies in the condition of zircon-reidite transformation, controversial models governing the transformation mechanism, and unclear effects of pre-existing radiation damage on reidite formation. Here, we show enhanced reidite formation by synchrotron X-ray diffraction, Raman spectroscopy, and transmission electron microscopy analyses of zircon grains that have experienced different alpha-decay doses from U and Th impurities and subsequent pressurization in diamond anvil cells. Below -1 x 10 18 alpha-decay events/g, the alpha-decay-induced isolated point defects in the still crystalline zircon facilitate the minor atomic readjustments required for reidite formation. However, above this dose, the loss of long-range periodicity in severely damaged or even metamict zircon inhibits the transformation. The enhanced reidite formation by minor radiation damage coincides with the more common occurrence of reidite at impact sites for which the precursor zircon has a relatively lower alphadecay-event dose before the impact event. In addition, the detailed atomic-scale structures of twinned reidite provide unambiguous evidence for a characteristic internal stress-induced martensitic transition. These findings have important implications for interpreting the formation conditions of natural reidite due to the convergence of pressure from the static, shockwave, and natural reidite samples.

This contribution provides a thorough examination of the structural characteristics of pyrochlore-type lanthanide titanates and zirconates Ln(2)Ti(2)O(7) and Ln(2)Zr(2)O(7), across various length scales. This paper also examines their processing, interesting physical properties (electrical, magnetic, and thermal characteristics), and responses to high pressure and ion irradiation. Brief sections on the elemental oxides' crystal chemistry, pertinent phase diagrams, and energetics of defect formation are also provided. Pyrochlore-type Ln(2)Ti(2)O(7) and Ln(2)Zr(2)O(7) stand out as truly multifunctional materials. Moreover, they have emerged as fascinating materials due to magnetic geometrical frustration, arising from the ordering of magnetic Ln(3+) and non-magnetic Ti4+ (or Zr4+) cations into separate, interpenetrating lattices of corner-sharing tetrahedra. This results in a diverse array of exotic magnetic ground states, such as spin-ice (e.g., Dy2Ti2O7 or Ho2Ti2O7) or quantum spin ice (e.g., Tb2Ti2O7), observed at both low and room temperatures. They also exhibit varied electrical and electrochemical characteristics. Some members such as Gd2Zr2O7, function as fast ion conductors with a conductivity (sigma) of approximate to 10(-2) Scm(-1) at 800 degrees C and activation energy (E-a) ranging from 0.85 to 1.52 eV, depending on the degree of structural disorder. Others, such as Gd2TiMoO7, are mixed ionic-electronic conductors with sigma approximate to 25 Scm(-1) at 1000 degrees C, making them promising candidate materials for applications in energy conversion and storage devices and oxygen separation membranes. Their exceptionally low thermal conductivity (e.g., kappa similar to 1.1-1.7 Wm(-1)K-1 between 700 and 1200 degrees C for Ln(2)Zr(2)O(7)), close to the glass-like lower limit of highly disordered solids, positions them as valuable materials for thermal barrier coatings. They can also effectively accommodate actinides (e.g., Pu, Np, Cm, Am) in solid solutions and sustain prolonged exposure to radiation due to alpha-decay events, while preserving the integrity of the periodic atomic structure. Proposed as major components in actinide-bearing ceramics, they contribute to the long-term immobilization and disposal of long-lived waste radionuclides from nuclear programs. Some of these properties are displayed simultaneously, opening avenues for new applications. Despite the wealth of data available in the literature, this review highlights the need for a better understanding of order/disorder processes in pyrochlore-type materials and the influence of the structural length scale on their physical and chemical properties. Recent experimental evidence has revealed that pyrochlore short-range structure is far more complex than originally thought. Moreover, pyrochlore local structure is now believed to include short-range, lower symmetry, ordered domains, such as the orthorhombic weberite-type of structure. Notably, short- and long-range structures appear decoupled across different length scales and temperature regimes, and these differences persist even in well-ordered samples. We believe that the pyrochlore structure offers a unique opportunity for examining the interplay between chemical composition, defect chemistry, and properties. (c) 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/)

The behavior of microcrystalline zirconium carbide (ZrC) and hafnium carbide (HfC) was studied under highly ionizing irradiation conditions at room temperature. The induced structural modifications were characterized via synchrotron-based X-ray diffraction experiments. Unit-cell expansion and buildup of microstrain were determined across a wide fluence range and linked to chemical compositions of the target material. The observed swelling resulting from irradiation with 198 MeV Xe ions in both carbide materials is characterized by two distinct mechanisms that operate within different fluence regimes. Unit-cell expansion initially proceeds by a direct-impact behavior that reaches saturation, followed at higher fluences by a second, linear swelling regime. The overall behavior, particularly the direct-impact regime, is similar for ZrC and HfC, with a more pronounced second defect accumulation process in HfC. Swelling in ZrC shows the same two distinct mechanisms upon irradiation with 198 MeV Xe ions and 946 MeV Au ions, but swelling induced by the lower-energy ions is greater across the entire fluence series. Accounting for the difference in energy deposition density between the two irradiation conditions reveals that the first swelling mechanism (direct-impact behavior) is likely related to the formation of more simple defects. In contrast, the second damaging mechanism at higher fluences (linear increase) cannot be fully explained by the induced energy density, and swelling remains somewhat higher for the low-velocity Xe irradiation. This may suggest that more complex defects and defect clusters are responsible for this swelling regime, with either their size and/or morphology modified at different energy densities.

Sesquioxides (M2O3) exhibit rich polymorphism with distinct phases that form over broad compositional, pressure, and temperature ranges. This makes these materials an ideal model system for studying the effects of high-energy ball milling and the far-from-equilibrium conditions induced by complex mechanical interactions. Polycrystalline bixbyite-structured binary sesquioxides (M2O3, M = Gd, Dy, Ho, Er, Yb, and Y) were processed by high-energy ball milling and the resulting structural modifications were characterized by synchrotron X-ray diffraction. Ball milling drives the initial cubic structure ("C-type") in each oxide to the monoclinic, "B-type" structure, with the rate of formation and maximum attainable phase fraction dependent on the cation size. The B-type phase fraction increases with milling time for each sesquioxide, but reaches steady-state behavior below unity, which contrasts with previous studies that induced a complete transformation by exposure to temperature, pressure, or ion radiation. This behavior suggests a complex interaction regime within a planetary ball mill characterized by transient processes, which exert simultaneous 1) driving forces to form the B-type phase and 2) kinetic pathways to partially recover the C-type phase. We show that these two processes are correlated with the effects of pressure and temperature during mechanical interactions between the sample and milling tools. Sesquioxides (M2O3) undergo polymorphic transitions during high-energy ball milling, transitioning from a cubic structure to a monoclinic structure. The rate and extent of the transition depend on the cation, with steady-state behavior reached before complete transformation. Partial recovery of the cubic phase indicates complex interactions during milling, involving pressure and temperature.image (c) 2024 WILEY-VCH GmbH

The atomic structures of the lanthanide tantalates, Ln3TaO7, series (Ln = Pr, Tb, Dy, Ho, Tm, Yb) were systematically investigated using total scattering techniques.