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Uranyl oxide hydrate phases with heavy lanthanide ions: [Ln(UO2)2O3(OH)]·0.5H2O (Ln = Tb, Dy, Ho and Yb)
(Royal Society of Chemistry, 2018-05-16) Zhang, YJ; Aughterson, RD; Karatchevtseva, I; Kong, LG; Tran, TT; Čejka, J; Aharonovich, I; Lumpkin, GR
Four uranyl oxide hydrate phases with heavy lanthanide ions, [Ln(UO2)2O3(OH)]·0.5H2O [Ln = Tb (1), Dy (2), Ho (3) and Yb (4)], have been synthesized under hydrothermal conditions at 240 °C and characterized. SEM-EDS revealed that these phases have very similar thin plate morphologies with a U to Ln atomic ratio of 2 : 1, which is further confirmed by TEM-EDS. Their high magnification TEM bright field images showed small crystalline domains (∼2–5 nm) with preferred crystal orientations. Both XRD and TEM SAED confirmed that they crystallize in the trigonal crystal system with the P[3 with combining macron]m1 space group. Raman characterization revealed the typical vibration modes for the uranyl units with the calculated U[double bond, length as m-dash]O bond lengths are comparable to the values reported for other UOH phases with d-transition metal ions as the interlayer species. The possible presence of a pentavalent uranyl unit has been ruled out by UV-vis-NIR spectroscopy. The thermal and optical properties have also been investigated and reported. © Royal Society of Chemistry 2025.
Design and performance of the variable-wavelength Bonse–Hart ultra-small-angle neutron scattering diffractometer KOOKABURRA at ANSTO
(International Union of Crystallography, 2018-02-01) Rehm, C; de Campo, L; Brûlé, A; Darmann, FA; Bartsch, FJK; Berry, A
The double-crystal ultra-small-angle neutron scattering (USANS) diffractometer KOOKABURRA at ANSTO was made available for user experiments in 2014. KOOKABURRA allows the characterization of microstructures covering length scales in the range of 0.1–10 µm. Use of the first- and second-order reflections coming off a doubly curved highly oriented mosaic pyrolytic graphite premonochromator at a fixed Bragg angle, in conjunction with two interchangeable pairs of Si(111) and Si(311) quintuple-reflection channel-cut crystals, permits operation of the instrument at two individual wavelengths, 4.74 and 2.37 Å. This unique feature among reactor-based USANS instruments allows optimal accommodation of a broad range of samples, both weakly and strongly scattering, in one sample setup. The versatility and capabilities of KOOKABURRA have already resulted in a number of research papers, clearly demonstrating that this instrument has a major impact in the field of large-scale structure determination. © International Union of Crystallography.
Preparation of cerium titanate brannerite by solution combustion, and phase transformation during heat treatment
(Elsevier, 2017-05) Kong, LG; Gregg, DJ; Vance, ER; Karatchevtseva, I; Lumpkin, GR; Blackford, MG; Holmes, R; Jovanovic, M; Triani, G
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 (TiO2, CeO2 and brannerite CeTi2O6) 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 TiO2 and CeO2 were present after 1200 °C calcination. The brannerite CeTi2O6 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. © 2017 Published by Elsevier Ltd.
Synthesis of hierarchical mesoporous Ln 2Ti2O7 (Ln = Y, Tb–Yb) pyrochlores and uranyl sorption properties
(Elsevier, 2022-06) Kong, LG; Karatchevtseva, I; Wei, T; Scales, N
Mesoporous structured metal oxides exhibit many active applications. However, the synthesis of crystalline metal oxides with a ternary composition while maintaining satisfactory pore features is challenging. Typically, high temperatures are required which inhibit control of pore structure properties including surface area, pore volume, and pore size. Herein, the synthesis of ternary metal oxides Ln2Ti2O7 possessing pyrochlore crystal structure is achieved using a novel technique which combines ‘soft’ and hard colloid templating strategies. The formed materials are of submicron size and composed of ∼ 25–30 nm product ‘building blocks’ with good chemical and phase stability. The polycrystalline powders have a high specific surface area (up to 70 m2•g–1) and pore volume (∼ 0.35 cm3•g–1) which result in a good adsorption capacity (U uptake closing to 60 mg•g–1). Remarkably, the material exhibits a significant portion of mesopores (mainly 10–40 nm) which facilitate fast adsorption of the cations due to high accessibility. The synthetic methodology described herein produces highly homogenous powders and can be applied to other compositions and structures. © 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.
The giant piezoelectric effect: electric field induced monoclinic phase or piezoelectric distortion of the rhombohedral parent?
(IOP Publishing, 2003-05-19) Kisi, EH; Piltz, RO; Forrester, JS; Howard, CJ
Lead zinc niobate-lead titanate (PZN-PT) single crystals show very large piezoelectric strains for electric fields applied along the unit cell edges e.g. [001]R. It has been widely reported that this effect is caused by an electric field induced phase transition from rhombohedral (R3m) to monoclinic (Cm or Pm) symmetry in an essentially continuous manner. Group theoretical analysis using the computer program ISOTROPY indicates phase transitions between R3m and Cm (or Pm) must be discontinuous under Landau theory. An analysis of the symmetry of a strained unit cell in R3m and a simple expansion of the piezoelectric strain equation indicate that the piezoelectric distortion due to an electric field along a cell edge in rhombohedral perovskite-based ferroelectrics is intrinsically monoclinic (Cm), even for infinitesimal electric fields. PZN-PT crystals have up to nine times the elastic compliance of other piezoelectric perovskites and it might be expected that the piezoelectric strains are also very large. A field induced phase transition is therefore indistinguishable from the piezoelectric distortion and is neither sufficient nor necessary to understand the large piezoelectric response of PZN-PT. © IOP Publishing

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