Gd-doped CeO(2) exhibits an anomalously large electrostriction effect generating stress that can reach 500 MPa. In situ XANES measurements indicate that the stress develops in response to the rearrangement of cerium-oxygen vacancy pairs. This mechanism is fundamentally different from that of materials currently in use and suggests that Gd-doped ceria is a representative of a new family of high-performance electromechanical materials.

Realizing laterally continuous ultra-thin gold films on transparent substrates is a challenge of significant technological importance. In the present work, formation of ultra-thin gold films on fused silica is studied, demonstrating how suppression of island formation and reduction of plasmonic absorption can be achieved by treating substrates with (3-mercaptopropyl) trimethoxysilane prior to deposition. Void-free films with deposition thickness as low as 5.4 nm were realized and remained structurally stable at room temperature. Based on detailed structural analysis of the films by specular and diffuse X-ray reflectivity measurements, it is shown that optical transmission properties of continuous ultra-thin films can be accounted for 2 using the bulk dielectric function of gold. However, it is important to take into account the non-abrupt transition zone between the metal and the surrounding dielectrics, which extends through several lattice constants for the laterally continuous ultra-thin films (film thickness below 10 nm). This results in a significant reduction of optical transmission, as compared to the case of abrupt interfaces. These findings imply that the atomic-scale interface structure plays an important role when continuous ultra-thin films are considered, e.g., as semitransparent electrical contacts, since optical transmission deviates significantly from the theoretical predictions for ideal films.

The kinetics of point‐defect association/dissociation reactions in Ce0.8Gd0.2O1.9 and their influence on the crystal lattice parameter are investigated by monitoring thermally induced stress and strain in substrate‐ and self‐supported thin films. It is found that, in the temperature range of 100–180 °C, the lattice parameter of the substrate‐supported films and the lateral dimensions of annealed, self‐supported films both exhibit a hysteretic behavior consistent with dissociation/association of oxygen vacancy–aliovalent dopant complexes. This leads to strong deviation from linear elastic behavior, denoted in the authors' previous work as the “chemical strain” effect. At room temperature, the equilibrium state of the point defects is reached within a few months. During this period, the lattice parameter of the substrate‐supported films spontaneously increases, while the self‐supported films are observed to transform from the flat to the buckled state, indicating that formation of the dopant–vacancy complex is associated with a volume increase. The unexpectedly slow kinetics of establishing the defect equilibrium at room temperature can explain the fact that, depending on the sample history, the “observable” lattice parameters of Ce0.8Gd0.2O1.9, as reported in the literature, may differ from one another by a few tenths of a percent. These findings strongly suggest that the lattice parameter of the materials with a large concentration of interacting point defects is a strong function of time and material preparation route.

In this study, multi-phase borosilicate-based glass-ceramics were investigated as an alternative waste form for immobilizing non-fissionable products from used nuclear fuel. Currently, borosilicate glass is the waste form selected for immobilization of this waste stream, however, the low thermal stability and solubility of MoO 3 in borosilicate glass translates into a maximum waste loading in the range 15-20 mass%. Glass-ceramics provide the opportunity to target chemically durable crystalline phases, e.g., powellite, oxyapatite, celsian, and pollucite that will incorporate MoO 3 as well as other waste components such as lanthanides, alkalis, and alkaline earths at levels twice the solubility limits of a single-phase glass. In addition a glassceramic could provide higher thermal stability, depending upon the properties of the crystalline and amorphous phases. Here, glass-ceramics were synthesized at waste loadings of 42, 45, and 50 mass% with the following glass additives: B 2 O 3 , Al 2 O 3 , CaO, and SiO 2 by slow-cooling from a glass melt. Glass-ceramics were characterized in terms of phase assemblage, morphology, and thermal stability. Only two of the targeted phases, powellite and oxyapatite, were observed, along with lanthanide-borosilicate and cerianite. Results of this initial investigation show promise of glass-ceramics as a potential waste form to replace single-phase borosilicate glass.

As a major component in the nuclear fuel cycle, octoxide uranium is subjected to intensive nuclear forensics research. Scientific efforts have been mainly dedicated to determine signatures, allowing for clear and distinct attribution. The oxygen isotopic composition of octoxide uranium, acquired during the fabrication process of the nuclear fuel, might serve as a signature. Hence, understanding the factors governing the final oxygen isotopic composition and the chemical systems in which U3O8 was produced may develop a new fingerprint concerning the history of the material and/or the process to which it was subjected. This research determines the fractionation of oxygen isotopes at different temperatures relevant to the nuclear fuel cycle in the system of U3O8 and atmospheric O2. We avoid the retrograde isotope effect at the cooling stage at the end of the fabrication process of U3O8. The system attains the isotope equilibrium at temperatures higher than 300 °C. The average δ18O values of U3O8 in equilibrium with atmospheric oxygen have been found to span over a wide range, from −9.90‰ at 300 °C up to 18.40‰ at 800 °C. The temperature dependency of the equilibrium fractionation (1000 ln αU3O8‑atm. O2 ) exhibits two distinct regions, around −33‰ between 300 °C and −500 °C and −5‰ between 700 °C and −800 °C. The sharp change coincides with the transition from a pseudo-hexagonal structure to a hexagonal structure. A depletion trend in δ18O is associated with the orthorhombic structure and may result from the uranium mass effect, which might also play a role in the depletion of 5‰ versus atmospheric oxygen at high temperatures.

Cerium oxide, in both pure and doped forms, is one of the most important and extensively studied oxygen ion conductors. It exhibits a number of interesting properties including ionic conductivity due to the high mobility of oxygen vacancies, a series of different phases formed upon reduction, [1] dependence of the lattice parameter and electrical properties on grain size, [2] and non-linear elastic effects, which have been named ''chemical stress '' [3] and ''chemical strain''. [4][5][6] Recent structural studies, both theoretical [7] and experimental, [8][9][10] have been aimed at understanding the mechanism of interaction between the cations and the oxygen vacancies. These interactions are thought to be directly responsible for a number of effects such as resistance to radiation damage, [11] vacancy ordering leading to phase transformations, [1,12,13] dependence of ionic conductivity on the ionic radius of the dopant, [14] and the non-linear elastic effects. Furthermore, in addition to the fluorites, cation-vacancy interactions are observed in a number of other solids with a large concentration of oxygen vacancies, for instance, perovskites. [15] Therefore, characterizing the details of cation-vacancy interactions in Ce 0.8 Gd 0.2 O 1.9 may have implications for a wider range of materials.One property in which the cation-vacancy interaction is thought to be directly implicated is the chemical strain effect, which is the ability of thin films of Ce 0.8 Gd 0.2 O 1.9 to exhibit two different elastic moduli at temperatures below 200 8C. [5,6] This effect is accompanied by an absolute change in volume of $0.2% even when the external stress is homogeneous, which distinguishes it from the Gorsky, Snoek [16] or Zener [17] effects. The chemical strain effect has been tentatively attributed to a change in specific volume due to the interaction of the Gd 3þ ions with oxygen vacancies (5% of all oxygen sites in Ce 0.8 Gd 0.2 O 1.9 [4,5,18] ). However, no evidence has been presented that the rearrangement of vacancies in Ce 0.8 Gd 0.2 O 1.9 can be stress-induced, or even takes place at all. The present study uses extended X-ray absorption fine-structure (EXAFS) spectroscopy to evaluate the local structure of strain-free nanocrystalline films of Ce 0.8 Gd 0.2 O 1.9 and to compare it with that of Ce 0.8 Gd 0.2 O 1.9 films with in-plane compressive strain of 0.3% AE 0.1%. Since the lattice parameter of Ce 0.8 Gd 0.2 O 1.9 varies by a few tenths of a percent, depending on the preparation route and sample history, [6] the X-ray diffraction (XRD) and EXAFS measurements were performed on the same samples, thus permitting direct comparison of the local ion arrangement with the long-range structure. We report that even in strain-free Ce 0.8 Gd 0.2 O 1.9 , interaction of oxygen vacancies with Ce 4þ ion neighbors is favored, rather than interaction with Gd 3þ ion neighbors. As a result, Ce 4þ ions are shifted away from the oxygen vacancies. Furthermore, compressive strain of 0.3% AE 0.1% causes the CeÀO bond to contract by 1.0% ...

The chemical strain effect describes a mechanism of stress relaxation in solids that can be attributed to the conversion of elastic energy into chemical energy of point defects. Experimental confirmation of this effect is presented here for the case of thin self‐supported films of the ionic conductor Ce0.8Gd0.2O1.9. If heated slowly, (< 5 °C min–1) these films remain flat within the temperature range of 25–180 °C. If heated more rapidly than ∼ 20 °C min–1, the films buckle above 53 °C, but after ∼ 3–30 min at elevated temperatures, they become flat again, demonstrating that stress‐relaxation has taken place. The degree of stress reduction observed is consistent with the value calculated for this system using Boltzmann statistics in the case of small strain. These findings confirm the concept of stress adaptability in solids that we introduced in Part I and suggest that a large class of such materials, which exhibit the chemical strain effect, is likely to be found.

Fabrication of continuous ultra-thin gold films ( < 10 nm) on the surface of optical polymers (CYCLOTENE and ORMOCLEAR) is reported. Using a range of electrical, optical and structural characterization techniques, we show that polymers can be superior to more conventional (inorganic) materials as optical substrates for realizing ultra-thin gold films. Using these transparent polymer substrates, smooth, patternable gold films can be fabricated with conventional deposition techniques at room temperature, without adhesion or seeding layers, facilitating new photonic and plasmonic nanostructures, including transparent electrical contacts, thin film waveguides, metamaterials, biosensors and high-contrast superlenses.