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The previously unattained fabrication of single phase Ln2ZrO5 (Ln = Sm, Eu, Gd, and Tb) compounds via relatively low sintering temperature (1400°C) is achieved in this study using a coprecipitation method. The crystal structures have been investigated by neutron, synchrotron X‐ray powder diffraction, and electron diffraction techniques. While the general long‐range structure may be well described by the defect‐fluorite type structure with Fm3¯$\bar{3}$m symmetry, electron diffraction has highlighted a complex underlying modulated structure that varies between each compound. These compounds have been tested for ion‐irradiation response using in situ 1 MeV krypton ions and transmission electron microscopy characterization. None of the compounds undergo a crystalline to amorphous transition, even holding at 50 K. Both the underlying fluorite and modulated superstructures are little affected by the irradiation. However, some atomic rearrangements are observed in the postirradiated electron diffraction patterns for the Sm2ZrO5 specimen. [ABSTRACT FROM AUTHOR]

The crystal structures of seven samples of orthorhombic ( Pnma ) Ln 2 TiO 5 compounds with Ln =La, Pr, Nd, Sm, Gd, Tb and Dy were refined by Rietveld analysis of synchrotron X-ray powder diffraction (S-XRD) data. With increasing size of the lanthanide cation, the lattice parameters increase systematically: c by only ~1.5% whereas both a and b by ~6% from Dy 2 TiO 5 to La 2 TiO 5 . The mean Ti–O bond length only increases by ~1% with increasing radius of the Ln cation from Gd to La, primarily due to expansion of the pair of Ti–O 3 bonds to opposite corners of the Ti–O 5 square based pyramid polyhedra. For Dy 2 TiO 5 and Tb 2 TiO 5 , a significant variation in Ti–O 1 and Ti–O 4 bond lengths results in an increased deformation of the Ti–O 5 base. The particular configuration consists of large rhombic shaped tunnels and smaller triangular tunnels along the b axis, which have implications for defect formation and migration caused by radiation damage or the ionic conductivity. [ABSTRACT FROM AUTHOR]

Abstract: A series of single phase compounds with nominal stoichiometry Sm(x)Yb(2−x)TiO5 (x=2, 1.4, 1, 0.6, and 0) have been successfully fabricated to generate a range of crystal structures covering the most common polymorphs previously discovered in the Ln 2TiO5 series (Ln=lanthanides and yttrium). Four of the five samples have not been previously fabricated in bulk, single phase form so their crystal structures are refined and detailed using powder synchrotron and single crystal x-ray diffraction, neutron diffraction and transmission electron microscopy. Based on the phase information from diffraction data, there are four crystal structure types in this series; orthorhombic Pnma, hexagonal P63 /mmc, cubic (pyrochlore-like) Fd-3m and cubic (fluorite-like) Fm-3m. The cubic materials show modulated structures with variation between long and short range ordering and the variety of diffraction techniques were used to describe these complex crystal structure types. [Copyright &y& Elsevier]

An aqueous solution route was employed to prepare cerium titanate oxide brannerite. Thermal analysis, X-ray diffraction, Raman spectroscopy, transmission and scanning electron spectroscopy, were used to investigate the brannerite structure formation and bulk properties. Mixed metal oxides (TiO 2 , CeO 2 and brannerite CeTi 2 O 6 ) were formed upon calcination at 800 °C for 12 h. The amount of brannerite phase decreased to form the constituent oxides with increasing calcination temperature and only pure TiO 2 and CeO 2 were present after 1200 °C calcination. The brannerite CeTi 2 O 6 phase reformed at 1300 °C, and its relative amount was increased with dwell time. After 48 h calcination at 1300 °C, brannerite with only minor metal oxide impurities (<1%) was observed. The sample melted at 1400 °C which led to the collapse of brannerite back to its constituent oxides. Further, the phase formation was influenced by pelletization of the powders, which may be explained by a molar volume increase during brannerite formation. Attempts to confirm this hypothesis using Pu brannerite were inconclusive. [ABSTRACT FROM AUTHOR]

CVD diamond is irradiated by 5 MeV carbon ions, with each sample held at a different temperature (300–873 K) during irradiations. The defect structures resulting from the irradiations are evident as vacancy, interstitial and amorphous carbon signals in Raman spectra. The observed variation of the full width at half maximum (FWHM) and peak position of the diamond peak suggests that disorder in the diamond lattice is reduced for high temperature irradiations. The dumbbell interstitial signal is reduced for irradiations at 873 K, which suggests this defect is unstable at these temperatures and that interstitials have migrated to crystal surfaces. Near edge X-ray absorption fine structure (NEXAFS) spectroscopy results indicate that damage to the diamond structure at the surface has occurred for room temperature irradiations, however, this structure is at least partially recovered for irradiations performed at 473 K and above. The results suggest that, in a high temperature irradiation environment such as a nuclear fusion device, in situ annealing of radiation-created defects can maintain the diamond structure and prolong the lifetime of diamond components. [ABSTRACT FROM AUTHOR]

Three neodymium (Nd) coordination polymers with propionate, succinate and mixed succinate–oxalate ligands have been synthesized and structurally characterized. Nd 2 (C 3 H 5 O 2 ) 6 (H 2 O) 3 ·3H 2 O ( 1 ) has a 1D polymeric structure built with both ninefold and ten-fold coordinated neodymium polyhedra linked through μ 2 -bridging propionate ligands. Nd 2 (C 4 H 4 O 4 ) 3 (H 2 O) 2 ( 2 ) has a 3D polymeric structure constructed with two distinct ninefold coordinated neodymium polyhedra linked through three types of succinate ligands, two in μ 4 - and one in μ 3 -coordination modes. Nd 2 (C 4 H 4 O 4 ) 2 (C 2 O 4 )(H 2 O) 4 ·3H 2 O ( 3 ) is built with two types of ten-fold coordinated neodymium polyhedra linked through μ 4 -succinate ligands into 2D undulating layers which are further connected through μ 2 -oxalate ligands forming a 3D network with channels. Their vibrational modes and thermal stabilities have been further investigated. [ABSTRACT FROM AUTHOR]

A novel soft chemistry route was developed to synthesize Y 2 Hf x Ti 2− x O 7 (0≤ x ≤2.0) oxide solid solution. An aqueous solution containing reactants was produced to ensure the combustion reaction taking place at the molecular level. A suite of characterization techniques, including X-ray diffraction, Raman, transmission electron spectroscopy, as well as X-ray absorption near edge structure (XANES), is employed to investigate the structural and phase changes of the series. Both X-ray and electron diffraction patterns show that the Y 2 Hf x Ti 2− x O 7 system undergoes a clear composition-induced phase transition from ordered pyrochlore to disordered defect-fluorite at x ~1.5. On the other hand, Raman and XANES spectra reveal a gradual evolution of the local structure with the substitution of Hf for Ti. [ABSTRACT FROM AUTHOR]

Two thorium(Th) complexes with lactate or formate have been synthesized and characterized. Th(C 3 H 5 O 3 ) 4 (H 2 O) 2 ( 1 ) [C 3 H 5 O 3 H = lactic acid] has a mononuclear structure with ten-fold coordinated Th polyhedron in deformed bicapped square antiprism by four chelating lactate ligands via both carboxylate O and the alcohol O atoms in addition to two coordinated water molecules. The lactate ligands are enantiomer with equal proportion of R - and S -isomers. [Th 6 (O) 4 (OH) 4 (HCO 2 ) 12 (H 2 O) 6 ]·5H 2 O ( 2 ) [HCO 2 H = formic acid] is a hexanuclear Th nanocluster constructed by four oxo-, four hydroxyl, twelve μ 2 -bridging formate ligands and six water molecules. The calculated bond valence sums are in good agreement with the presence of equal numbers of oxo- and hydroxyl groups in the cluster. Thermal studies confirmed that both complexes lost water molecules first followed by the decomposition of the organic ligands to form ThO 2 as the final product. The presence of bridging OH-groups in both complexes has been proven by Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Abstract: A series of uranium-containing gadolinium zirconate samples have been fabricated at 1450°C in oxidizing, inert and reducing atmospheres. X-ray diffraction, Raman spectroscopy and transmission electron microscopy have been utilized to confirm adoption of pyrochlore or defect fluorite structures. X-ray diffraction allowed determination of the bulk averaged structure while Raman spectroscopy and transmission electron microscopy were used to determine ordering at the microdomain scale. Diffuse reflectance, X-ray absorption near edge structure and X-ray photoelectron spectroscopies indicated a predominantly U6+ oxidation state for all the air-sintered samples, even when Ca2+ or A-site vacancies were incorporated to charge balance for U4+, a mixed U5+/U6+ oxidation state was found for samples sintered in argon, while a mixed U4+/U5+ oxidation state occurred for sintering under N2–3.5%H2. This demonstrates a degree of uranium oxidation state control through sintering conditions, and the potential of using gadolinium zirconates as host materials for uranium in nuclear waste applications. [Copyright &y& Elsevier]

Abstract: Calixarene-based picolinamides and malonamides are among the promising extracting ligands for selective separation of minor actinides. However, the understanding of coordination chemistry of actinide ions with simple picolinamide- and malonamide-type ligands is still far from comprehensive. In this work, we report the first two picolinamide coordinated uranium (VI) and thorium (IV) complexes with different 1D polymeric structures as well as a malonamide coordinated uranium (VI) molybdate with a 2D layered structure. [Copyright &y& Elsevier]

Reaction of UO2(NO3)2, NaOH, H2O2, and H3BO3 in aqueous solution leads to the formation of yellow crystals of Na14 [(UO2)(O2)1.5] 28·nH2O (I) at pH 8.5 within a few days, followed by transformation of (I) at room temperature to light yellow-green crystals of Na6 [UO2{B16O24(OH)8}] ·14H2O (II) (<80% yield). [ABSTRACT FROM AUTHOR]