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Proton irradiation with a primary ion energy of 2 MeV was used to simulate radiation damage in UN and (U,Zr)N fuel pellets. The pellets, nominally at room temperature, were irradiated to peak levels of 0.1, 1, 10 dpa and 100.0 dpa resulting in a peak hydrogen concentration of at most 90 at. %. Microstructure and mechanical properties of the samples were investigated and compared before and after irradiation. The irradiation induced an increase in hardness, whereas a decrease in Young’s modulus was observed for both samples. Microstructural characterization revealed irradiation-induced cracking, initiated in the bulk of the material, where the peak damage was deposited, propagating towards the surface. Additionally, transmission electron microscopy was used to study irradiation defects. Dislocation loops and fringes were identified and observed to increase in density with increasing dose levels. The high density of irradiation defects and hydrogen implanted are proposed as the main cause of swelling and consequent sample cracking, leading simultaneously to increased hardening and a decrease in Young's modulus.

This study presents a novel approach for the synthesis of WC-Ni cemented carbides with enhanced mechanical properties. A low-cost solution-based route was used to coat WC powders with well-distributed metallic nickel dots measuring between 17 nm and 39 nm in diameter. Varying compositions with loadings of 2, 6, and 14 vol% Ni were consolidated using spark plasma sintering (SPS) at 1350 degrees C under 50 MPa of uniaxial pressure giving relative densities of 99 +/- 1 %. The sintered WC-Ni cemented carbides had an even distribution of the Ni binder phase in all compositions, with retained ultrafine WC grain sizes of 0.5 +/- 0.1 mu m from the starting powder. The enhanced sinterability of the coated powders allowed for consolidation to near theoretical densities, with a binder content as low as 2 vol%. This is attributed to the uniform distribution of nickel and an extensive Ni-WC interface existing prior to sintering. The small size of the Ni dots likely also contributed to the solid-state sintering starting temperatures of as low as 800 degrees C. The mechanical performance of the resulting cemented carbides was evaluated by measuring the hardness at temperatures between 20 degrees C and 700 degrees C and estimating toughness at room temperature using Vickers indentations. These results showed that the mechanical properties of the WC-Ni cemented carbides synthesised by our method were comparable to conventionally prepared WC-Co cemented carbides with similar grain sizes and binder contents and superior to conventionally prepared WC-Ni cemented carbides. In particular, the 2 vol% Ni composition had excellent hardness at room temperature of up to 2210HV10, while still having an indentation fracture toughness of 7 MPa.m(0.5). Therefore, WC-Ni cemented carbides processed by this novel approach are a promising alternative to conventional WC-Co cemented carbides for a wide range of applications.

Nanocrystalline ZnO sponges doped with 5 mol% EuO1.5 are obtained by heating metal–salt complex based precursor pastes at 200–900 °C for 3 min. X-ray diffraction, transmission electron microscopy, and extended X-ray absorption fine structure (EXAFS) show that phase separation into ZnO:Eu and c-Eu2O3 takes place upon heating at 700 °C or higher. The unit cell of the clean oxide made at 600 °C shows only ≈0.4% volume increase versus undoped ZnO, and EXAFS shows a ZnO local structure that is little affected by the Eu-doping and an average Eu3+ ion coordination number of ≈5.2. Comparisons of 23 density functional theory-generated structures having differently sized Eu-oxide clusters embedded in ZnO identify three structures with four or eight Eu atoms as the most energetically favorable. These clusters exhibit the smallest volume increase compared to undoped ZnO and Eu coordination numbers of 5.2–5.5, all in excellent agreement with experimental data. ZnO defect states are crucial for efficient Eu3+ excitation, while c-Eu2O3 phase separation results in loss of the characteristic Eu3+ photoluminescence. The formation of molecule-like Eu-oxide clusters, entrapped in ZnO, proposed here, may help in understanding the nature of the unexpected high doping levels of lanthanide ions in ZnO that occur virtually without significant change in ZnO unit cell dimensions.

Carbothermal reduction of Zr-sucrose gels powders into nano-phase ZrC, or ZrC-Zr(C,O) core-shell powders, via a composite of 2–4 nm sized ZrO2 and amorphous carbon, is described. Samples with 1.7–20 sucrose-carbon:Zr ratio gels heated to 1495 °C at 10 °Cmin−1, with 3 and 30 min hold time were studied in detail using; TG, XRD, SEM, TEM, STEM-EDX, and XPS with Ar+-ion etching. After 1495 °C, 3 min, the samples with 12-20C:Zr ratios yielded weakly agglomerated 30 to 40 nm sized ZrC particles, surrounded by a dense 5 nm thick shell of Zr(C,O). With 5C:Zr significant amounts of ZrO2 was present after heating at 1495 °C for 3 min, while after 30 min annealing, ZrC particles without residual amorphous carbon was obtained. Minor amounts of zirconia was found in most samples, which in similarity with the 5 nm Zr(C,O) shell, is believed to stem from post synthesis oxidation.

A carbothermal nitridation route to nanophase ZrN1-xCx powder using nitrogen gas and a highly homogeneous solution derived carbon-ZrO2 nanocomposite is described. Composites with 2-4 nm sized ZrO2 particles were prepared by hydrolysis of Zr(OPrn)(4) and sucrose with 2-8 sucrose-C:Zr and heating to 600 degrees C. The phase-evolution on heating was elucidated in detail using: TG-DTA, XRD, XPS, IR- and Raman spectroscopy, SEM-EDS, and TEM-EDS. With 5-8 C:Zr samples heated to 1495 degrees C, somewhat agglomerated single-crystalline Zr (N,C) particles in sizes centred around 40-90 nm were obtained, in some cases with minor amounts of r-Zr7O8N4 and m-ZrO2. The c-Zr(N,C) had slightly larger XRD cell-dimensions (a = 4.589-4.606 angstrom) than the literature ZrN (a = 4.5775 A), due to some carbon substitution in the nitrogen positions. The single-crystalline Zr(N,C) particle cores of the 8C:Zr, and to some extent 7C:Zr, samples, had a 4-6 nm thick distinctive amorphous or microcrystalline Zr(N,C,O) shell.

A fast, low cost solution route to nickel dot coated NbC powder using Ni(NO3)26H2O, Ni(OAc)24H2O and triethanolamine (TEA) as precursors in methanol solvent was developed. After mixing the precursor solution with 50-300 nm sized NbC powder and evaporation of the solvent, heating to 150 oC, or higher, yielded NbC powder evenly covered with well-dispersed nickel metal dots, 6 to 25 nm in size, depending on the nickel loading and temperature. Coatings yielding 4 to 14 wt% nickel loading were studied at temperatures from 200 to 700 oC, using TG-DTA, XRD, SEM, XPS with Ar+-ion etching, TEM/DF, and STEM/HAADF/EDS.

Thermal losses through vibrational coupling are critical bottlenecks limiting several materials classes from reaching their full potential. Altering the phonon–phonon and electron–phonon coupling by controlled suppression of vibrational degrees of freedom through low-dimensionality are promising but still largely unexplored approaches. Here we report a detailed study of the first- and second-order Raman processes as a function of size for low-dimensional ZnO. Wurtzite ZnO nanoparticles were synthesised into 3D frameworks of ZnO crystallites, with tailored crystallite diameters from 10 nm to 150 nm and characterised by electron microscopy, X-ray diffraction and non-resonant and resonant Raman spectroscopy. We present a short derivation of how resonance Raman and the relation between the longitudinal optical (LO) phonons can be utilised to quantify the electron–phonon coupling, its merits, and limitations. Theoretical Raman response using density functional theory is corroborating the experimental data in assigning first- and second-order Raman modes. The Lyddane-Sachs-Teller equation was applied to the measured LO–TO split and revealed no change in the ratio between the static and high-frequency dielectric constant with changing ZnO dimension from 10 nm to 150 nm. The second-order Raman revealed a phonon–phonon coupling that generally increased with particle size and markedly so for differential modes. Resonance Raman showed the fundamental LO mode and the 2nd, 3rd, and 4th overtones. The intensity relation between the fundamental LO mode and its overtones enabled the extraction of the change in electron–phonon coupling via the Huang-Rhys parameter as a function of particle size, which showed an increase with particle size.

A carbothermal nitridation route to nanophase ZrN1-xCx powder using nitrogen gas and a highly homogeneous solution derived carbon-ZrO2 nanocomposite is described. Composites with 2-4 nm sized ZrO2 particles were prepared by hydrolysis of Zr(OPrn)4 and sucrose with 2 to 8 sucrose-C:Zr and heating to 600 oC. The phase-evolution on heating was elucidated in detail using: TG-DTA, XRD, XPS, IR- and Raman spectroscopy, SEM-EDS, and TEM-EDS. With 5-8 C:Zr samples heated to 1495 oC, somewhat agglomerated single-crystalline Zr(N,C) particles in sizes centred around 40-90 nm) were obtained, in some cases with minor amounts of r-Zr7O8N4 and m-ZrO2. The c-Zr(N,C) had slightly larger XRD cell-dimensions (a = 4.589-4.606 Å) than the literature ZrN (a = 4.5775 Å), due to some carbon substitution in the nitrogen positions. The single-crystalline Zr(N,C) particle cores of the 8C:Zr, and to some extent 7C:Zr, samples, had a 4-6 nm thick distinctive amorphous or micro-crystalline Zr(N,C,O) shell.

The phase development during sintering of a 14 wt. % nano-dot nickel coated NbC powder was investigated using dilatometry and a combination of XRD, ToF-ERDA, PIXE, SEM-EDS/EBSD/TKD, TEM-EDS/EELS for analysis of samples heated to 1375, 1405 and 1500 oC with a 30 min annealing. The sintering at 1110-1375 oC, ended in a plateau-like step, centred at 1405 oC, before the final densification to 1500 oC. The textured binder phase in the dense composites consisted of fcc Nb0.15Ni0.85 and h-Nb0.2Ni0.8. Significant NbC grain-growth took place during heating at 1500 oC for 30 min; from ca. 0.5-5 mm at 1375 and 1405 oC (average 1 mm) to ca. 5-30 mm (average 10 mm). The XRD lattice parameters corresponded to compositions of NbC0.91-0.94 for the 1375-1500 oC, 30 min. annealed samples. The micro-hardness of the NbC phase was 1700-1900 (1375-1405 oC) to 1900-2300 HV0.05 (1500 oC, 30 min.), which is in line with the expected hardness for NbC0.91-0.94. The Ni-Nb alloy binder phase domains, possibly containing some small NbC particles, showed micro-hardnesses of 1150-1250 (1375-1405 oC) to 810 HV0.05 (1500 oC, 30 min.), which greatly exceeds nickel and is higher than Fe3Al.