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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]

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]