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The response of Ln 2 TiO 5 (where Ln is a lanthanide) compounds exposed to high-energy ions was used to test their suitability for nuclear-based applications, under two different but complementary conditions. Eight samples with nominal stoichiometry Ln 2 TiO 5 (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb and Dy), of orthorhombic ( Pnma ) structure were irradiated, at various temperatures, with 1 MeV Kr 2+ ions in-situ within a transmission electron microscope. In each case, the fluence was increased until a phase transition from crystalline to amorphous was observed, termed critical dose D c . At certain elevated temperatures, the crystallinity was maintained irrespective of fluence. The critical temperature for maintaining crystallinity, T c , varied non-uniformly across the series. The T c was consistently high for La, Pr, Nd and Sm 2 TiO 5 before sequential improvement from Eu to Dy 2 TiO 5 with T c 's dropping from 974 K to 712 K. In addition, bulk Dy 2 TiO 5 was irradiated with 12 MeV Au + ions at 300 K, 723 K and 823 K and monitored via grazing-incidence X-ray diffraction (GIXRD). At 300 K, only amorphisation is observed, with no transition to other structures, whilst at higher temperatures, specimens retained their original structure. The improved radiation tolerance of compounds containing smaller lanthanides has previously been attributed to their ability to form radiation-induced phase transitions. No such transitions were observed here. [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]

Highlights: [•] The incorporation of neptunium (Np) and plutonium (Pu) in thorutite (ThTi2O6) has been studied. [•] The effect of Np/Pu doping on the unit cell parameter changes has been discussed from the structure point of view. [•] The effect of Y as charge compensator to encourage the formation of higher valences of Np and Pu has been explored. [•] The resulting Np/Pu doped thorutite samples have been characterised by using XRD, SEM and DRS. [ABSTRACT FROM AUTHOR]

While Zn vacancies are regarded as the charge compensators in Ti-rich Zn2 TiO4, no evidence of cation vacancies in essentially single-phase samples containing up to 13 wt% excess TiO2 was evident from positron annihilation lifetime spectroscopy (PALS). Nor was there strong evidence of cation vacancies in Ta-doped samples targeted to contain either tetrahedral or octahedral vacancies, although there was a small increase in the lifetime as the doping level increased and the structure changed from cubic to tetragonal. [ABSTRACT FROM AUTHOR]

Pyrochlore Nd 2 Zr 2 O 7 nanoparticles were prepared by complex-precipitation in aqueous media, followed by calcination in MgO matrix and subsequent dissolution processing. A suite of characterization techniques, including X-ray diffraction, Raman, TEM, SEM, dynamic light scattering, and nitrogen sorption, was employed to investigate the structure and particle size of the synthesized nano materials. Results show that calcination at 1200 °C for 20 h forms Nd 2 Zr 2 O 7 with pyrochlore structure. The matrix phase (MgO) had no effect on the formation of pyrochlore phase. The MgO phase was readily removed by dissolution at 0.5 M HNO 3 aqueous solution; and the remaining pyrochlore Nd 2 Zr 2 O 7 nanoparticles had a diameter of approximately 200 nm estimated by TEM and approximately 550 nm determined by light scattering due to slight aggregation. The bulk density of the pelletized powder reached approximately 99% of theoretical value, after uniaxial pressing at 2.0–2.5 MPa and sintering at 1400 °C for 48 h. [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]

Cerium titanate CeTi2O6 was prepared by a new soft chemistry route in aqueous solution. A suite of characterization techniques, including X-ray diffraction, thermal analysis, vibrational spectroscopy, and scanning and transmission electron spectroscopy, were employed to S investigate the brannerite structure formation and its bulk properties. The J synthesized powder formed the brannerite crystal structure upon calcination at temperatures as low as 800°C. Samples sintered at 1350 °C possess a high level of crystallinity. X-ray absorption near-edge structure results indicate the presence of six-coordinated Ce4+ in the brannerite samples. [ABSTRACT FROM AUTHOR]

Abstract: Pyrochlore structured Nd2Sn x Zr2−x O7 (x=0–2) ceramics were prepared by a new chemical synthesis route in an aqueous media. Raman spectra and X-ray diffraction patterns confirmed the formation of the pyrochlore structure after sintering at 1400°C. SEM results showed pelletized materials became dense with increasing Zr/Sn mole ratio and sintering temperature. These candidate materials have characteristic structures for the development of nuclear waste forms or inert matrix nuclear fuels. [Copyright &y& Elsevier]

Two new double thorium oxalates with sodium ions have been prepared and characterized by using scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS), Raman spectroscopy and single-crystal X-ray diffraction. The crystal structure of Na4[Th(C2O4)4] ·5.5H2O ( 1) contains infinite chains, [Th(μ2-C2O4)2(C2O4)3] n4 n-, with three terminating bidentate and two bridging tetradentate oxalate ligands. The crystal structure of Na10[Th2(C2O4)9] ·15H2O ( 2) comprises unique dimers, [Th2(μ2-C2O4)(C2O4)8]10-, with Th atoms being coordinated by five oxalato ligands, four terminating bidentate and one bridging tetradentate. The structure is the first dimer of tetravalent actinide oxalato complexes. The spectroscopic results are in good agreement with the crystal structures. [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]

The title compound is synthesized in aqueous medium from a mixture of titanium(IV) bis(ammonium lactato)dihydroxide and Ce(NO3)3 (sintering between 800 and 1400 °C). [ABSTRACT FROM AUTHOR]