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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]

As part of a broader study of ceramic nuclear waste‐forms, four different lanthanide titanates were fabricated; La0.1Sm0.1Gd0.1Tb0.1Dy0.3Ho0.1Er0.2YbTiO5, Sm0.3Gd0.3Dy0.3Yb1.1TiO5, Sm0.1Gd0.4Dy0.4Yb1.1TiO5, and Sm0.2Gd0.2Dy0.2Yb1.4TiO5. The aim was to produce single‐phase novel materials with cubic symmetry, capable of incorporating a wide variety of cations and with acceptable radiation tolerance. The chemistry flexibility and radiation tolerance are some of the major desirable properties for nuclear waste‐form materials. By using multiple lanthanides the average lanthanide radius can be controlled and consequently the structure, along with properties such as radiation tolerance. The radiation tolerance was assessed using in situ 1 MeV krypton irradiation and transmission electron microscopy characterization. Those materials for which cubic symmetry was achieved displayed better radiation tolerance; a greater critical fluence of ions (Fc) was required for the crystalline to amorphous transition, and a lower temperature was required to maintain crystallinity (Tc) during irradiation. [ABSTRACT FROM AUTHOR]

Seven perovskite samples in the LaxSr1-3x/2TiO3 solid solution series were monitored in situ during irradiation with 1.0 MeV Kr2+ ions using the intermediate voltage electron microscope-Tandem User Facility (IVEM) at Argonne National Laboratory. All the perovskites pass through the crystalline-amorphous transformation. However, the critical temperature for amorphisation Tc of the LaxSr1-3x/2TiO3 perovskites varies nonlinearly with composition, decreasing from 394±3 K for SrTiO3 to a minimum of 275±1 K for La0.2Sr0.7TiO3, then increasing with composition again to 865±3 K for La0.67TiO3. In combination with the work of previous authors, the electron microscopy results and IVEM data in this study suggest that there is a vacancy-assisted recovery mechanism in the cubic perovskites with compositions in the range 0

We refine the crystal structures of a systematic series of compounds with the general composition Ho (x) Yb (2-x) TiO 5 (x = 2, 1.6, 1.2, 1, 0.8, 0.4, 0) and Er 2 TiO 5 and find a transition from defect-pyrochlore to defect-fluorite structure with increasing ytterbium content, decreasing lanthanide radius. Short-range structure modulations consisting of pyrochlore-like nano-domains are systematically characterised using transmission electron microscopy. We test the Kr 2+ 1 MeV ion-irradiation response of Ho 2 TiO 5 , HoYbTiO 5 , Yb 2 TiO 5 , and Er 2 TiO 5 , via the crystalline to amorphous transition observed by using the in-situ TEM approach. The critical dose of amorphisation, D c , was measured at various temperatures and used to calculate the critical temperature for maintaining crystallinity, T c . A trend of lower T c values with decreasing lanthanide radius is found. We describe a new approach for determining T c values using cross-sectional TEM analysis of ex-situ bulk irradiated, 1 MeV Se + , samples; Ho 2 TiO 5 , HoYbTiO 5 and Yb 2 TiO 5 . The results of D c and T c values using the two approaches vary; however the trends across the sample system remain the same. [ABSTRACT FROM AUTHOR]

The Ln 2 TiO 5 (Ln = lanthanides and yttrium) compounds find use in nuclear, electronic and battery applications but there is a lack of information correlating the synthesis, structure and properties of these materials. We give an in depth review of the current available literature on the Ln 2 TiO 5 compounds. New structural findings of the Tb x Yb 2−x TiO 5 (x = 0, 0.4, 0.8, 1, 1.2, 1.6, 2) compounds are detailed and their response to 1 MeV krypton ion exposure is discussed. A single phase Tb 2 TiO 5 sample with hexagonal symmetry is the first bulk, single phase, mono-lanthanide with this stoichiometry and symmetry to be reported. Thus this work brings together the current literature and illustrates the synthesis-structure-property relationships that are observed in this family. [ABSTRACT FROM AUTHOR]

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]

The interpretation of angular symmetries in electron nanodiffraction patterns from thin amorphous specimens is examined. It is found that in general there are odd symmetries in experimental electron nanodiffraction patterns. Using simulation, it is demonstrated that this effect can be attributed to dynamical scattering, rather than other divergences from the ideal experimental conditions such as probe-forming lens aberrations and camera noise. The departure of opposing diffracted intensities from Friedel's law in the phase grating formalism is calculated using a general structure factor for disordered materials. On the basis of this, a simple correction procedure is suggested to recover the kinematical angular symmetries, and thus readily interpretable information that reflects the symmetries of the original projected object. This correction is numerically tested using both the phase object and multislice calculations, and is demonstrated to fully recover all the kinematical diffracted symmetries from a simulated atomic model of a metallic glass. [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]

Davidite (A1-xM21O38) samples from five different geological localities contain approximately 0.2 to 9.5 wt% UO2 (0.02 to 0.65 atoms per formula unit) and <0.1 to 1.3 wt% ThO2 (<0.01 to 0.09 atoms per formula unit). Maximum amounts of other notable cations include 3.7 wt% V2O3, 4.1 wt% Cr2O3, 2.5 wt% Y2O3, 5.6 wt% La2O3, 6.0 wt% Ce2O3, 4.0 wt% MnO, 2.4 wt% ZnO, 2.7 wt% SrO, and 4.9 wt% PbO. As a result of the variation in age and Th-U content, the calculated α decay dose ranges from ~0.2 to 44 x 1016 α/mg (~0.06 to 14.5 dpa). For samples with ages of 275--295 Ma, the critical dose for amorphization based on electron diffraction is ~0.8 x 1016 α/mg. Natural davidite is commonly altered to rutile, ilmenite, titanite, and other minor phases. [ABSTRACT FROM AUTHOR]

Abstract: Thin crystals of La2O3, LaAlO3, La2/3TiO3, La2TiO5, and La2Ti2O7 have been irradiated in situ using 1MeV Kr2+ ions at the Intermediate Voltage Electron Microscope-Tandem User Facility (IVEM-Tandem), Argonne National Laboratory (ANL). We observed that La2O3 remained crystalline to a fluence greater than 3.1×1016 ionscm−2 at a temperature of 50K. The four binary oxide compounds in the two systems were observed through the crystalline–amorphous transition as a function of ion fluence and temperature. Results from the ion irradiations give critical temperatures for amorphisation (T c ) of 647K for LaAlO3, 840K for La2Ti2O7, 865K for La2/3TiO3, and 1027K for La2TiO5. The T c values observed in this study, together with previous data for Al2O3 and TiO2, are discussed with reference to the melting points for the La2O3–Al2O3 and La2O3–TiO2 systems and the different local environments within the four crystal structures. Results suggest that there is an observable inverse correlation between T c and melting temperature (T m ) in the two systems. More complex relationships exist between T c and crystal structure, with the stoichiometric perovskite LaAlO3 being the most resistant to amorphisation. [ABSTRACT FROM AUTHOR]

Polycrystalline synthetic samples of Y2Ti2−xSnxO7with x= 0.4, 0.8, 1.2, and 1.6, together with Nd2Zr2O7, Nd2Zr1.2Ti0.8O7, and La1.6Y0.4Hf2O7, were irradiated in situ in the intermediate voltage electron microscope (IVEM)-Tandem Facility at Argonne National Laboratory using 1.0 MeV Kr ions at temperatures of 50 to 650 K. Determination of the critical amorphization fluence (Fc) as a function of temperature has revealed a dramatic increase in radiation tolerance with increasing Sn content on the pyrochlore B site. Nonlinear least-squares analysis of the fluence-temperature curves gave critical temperatures (Tc) of 666 ± 4, 335 ± 12, and 251 ± 51 K for the Y2Ti2−xSnxO7samples with x= 0.4, 0.8, and 1.2, respectively. The sample with x= 1.6 appears to disorder to a defect fluorite structure at a fluence below 1.25 × 1015ions cm−2and remains crystalline to 5 × 1015ions cm−2at 50 K. Additionally, the critical fluence-temperature response curves were determined for Nd2Zr1.2Ti0.8O7and La1.6Y0.4Hf2O7, and we obtained Tcvalues of 685 ± 53 K and 473 ± 52 K, respectively, for these pyrochlores. Nd2Zr2O7did not become amorphous after a fluence of 2.5 × 1015ions cm−2at 50 K, but there is evidence that it may amorphize at a higher fluence, with an estimated Tcof ∼135 K. The observed Tcresults are discussed with respect to the predicted Tcvalues based upon a previously published empirical model (Lumpkin, G. R.; Pruneda, M.; Rios, S.; Smith, K. L.; Trachenko, K.; Whittle, K. R.; Zaluzec, N. J. J. Solid State Chem.2007, 180, 1512). In the Y2Ti2−xSnxO7pyrochlores, Tcappears to be linear with respect to composition, and is linear with respect to rA/rBand x(48f) for all samples investigated herein. [ABSTRACT FROM AUTHOR]

Abstract: The radiation tolerance of synthetic pyrochlore and defect fluorite compounds has been studied using ion irradiation. We show that the results can be quantified in terms of the critical temperature for amorphization, structural parameters, classical Pauling electronegativity difference, and disorder energies. Our results demonstrate that radiation tolerance is correlated with a change in the structure from pyrochlore to defect fluorite, a smaller unit cell dimension, and lower cation–anion disorder energy. Radiation tolerance is promoted by an increase in the Pauling cation–anion electronegativity difference or, in other words, an increase in the ionicity of the chemical bonds. A further analysis of the data indicates that, of the two possible cation sites in ideal pyrochlore, the smaller B-site cation appears to play the major role in bonding. This result is supported by ab initio calculations of the structure and bonding, showing a correlation between the Mulliken overlap populations of the B-site cation and the critical temperature. [Copyright &y& Elsevier]

Abstract: High-resolution neutron and synchrotron X-ray powder diffraction have been used to examine various compositions across the system (1−x)CaTiO3−xLa2/3TiO3. The structures at room temperature were determined according to composition: in Pbnm for 0⩽x⩽0.5, Ibmm for 0.50.5 in the current study based on our high-resolution neutron diffraction data. From in situ measurements to identify structures above room temperature, an approximate composition–temperature phase diagram has been constructed, involving four temperature-induced phase transitions: Pbnm→I4/mcm, Ibmm→I4/mcm, I4/mcm→Pm3¯m and Cmmm→P4/mmm. [Copyright &y& Elsevier]

Abstract: Garnets, A 3 B 2C3O12, are an important group of minerals and have potential uses in the safe immobilisation of high-level nuclear waste. They have been found naturally to incorporate Zr, Ti and Fe, three elements of interest in the safe storage of nuclear waste. Kimzeyite, Ca3(Zr,Ti)2(Si,Al,Fe)3O12, is a naturally occurring garnet that contains Zr in a high percentage∼30wt%. For such a material to be of potential immobilisation for nuclear waste the structure needs to be completely understood. Electron channelling studies have shown that the Zr/Ti cations are located on the Y-site, with the Al/Fe cations located on the Z-site. This work has investigated synthetic analogues of kimzeyite, Ca3(Zr,Hf)2(Al,Fe,Si)3O12, by neutron powder diffraction, using the C2 spectrometer at the Chalk River nuclear facility, coupled with 57Fe Mössbauer spectroscopy. Such work has allowed the structure of the synthetic material to be determined along with the distribution of cations across the X (CN=8), Y (CN=6), and Z (CN=4) sites. Results have shown that it is possible to synthesise Ca3(Zr,Hf)2(Al,Fe,Si)3O12 with a range of Al/Fe ratios containing Zr and Hf. The Mössbauer data has indicated the Fe is located on the Z site. The structural analyses show that the unit cell changes linearly as a function of composition, and analysis of the disorder indicates that the Zr, Hf reside on the Y site and the Al, Fe, and Si reside on the Z site. [Copyright &y& Elsevier]

Materials of composition CaZrTi2−2 x Nb x Fe x O7 with the fluorite-related zirconolite structure have been prepared. The 57Fe Mössbauer spectra show that iron is initially located in the five co-ordinate cation sites. As the iron content increases the iron enters the octahedral sites until, at a composition CaZrTi0.4Nb0.8Fe0.8O7, ca. 50% of the iron is five co-ordinate and the remainder is located in the octahedral sites. [ABSTRACT FROM AUTHOR]

The distribution of A-site cations in the perovskite system LaxSr1-3x/2TiO3 depends on the concentration of La3+ ions and associated vacancies. For small x (x⪝0.2), the substitutions are expected to be random. For x⩾0.55, the cations are ordered in such a way that successive layers of A-sites are occupied to greater and lesser degree, and this ordering drives a tetragonal distortion. For x from about 0.3 to 0.5, the X-ray patterns show diffuse peaks indicative of similar ordering, but this is not long-range order and no tetragonal distortion results. The lower temperature structures also exhibit out-of-phase tilting of the TiO6 octahedra, setting in at temperatures varying linearly with composition from 105 K for x=0, to about 650 K at x=2/3. [Copyright &y& Elsevier]

Studies the behavior of uranium (U) in zirconolite, CaZrTi2O7, which is an important constituent of synroc. Study of U in a range of atmospheres; Related pyrochlore-structured titanate phase; Processing atmosphere of solid materials to immobilize multivalent waste ions such as actinides.

Reports on a study to describe of alteration effects in members of the betafite subgroup of the pyrochlore and the behavior of the pyrochlore group of minerals in the presence of hydrothermal and low-temperature fluids. Description of samples used in the study; Alteration effects in the betafite samples; Effect of alteration on annealing products.

Presents a general chemical framework for the interaction of minerals of the pyrochlore subgroup with high-temperature fluids that evolve during host rock emplacement and with later, lower temperature hydrothermal fluids and ground waters. Sample description; Niobium oxide mineral reactions; Chemical effects of alteration.

We present a new methodology for laser-induced steady-state photoluminescence (PL) spectroscopy of Dy3+ that aims at a direct quantification of the amorphous fraction f a present in zircon (ZrSiO4), which undergoes a transition from a crystalline to a metamict state due to cumulative self-irradiation damage caused by the radioactive decay of substituted U and Th. Using state-of-the-art confocal spectrometers attached to optical microscopes, measurements may be performed non-destructively on the micrometre length-scale with the option to visualize radiation-damage patterns as revealed by hyperspectral PL maps. Zircon from the Ratnapura district (Sri Lanka, ~520 Ma), was used as reference material to substantiate the applicability of the proposed method. The accumulation of radiation damage in this material was investigated in detail and obtained f a values correlate with calculated ff-doses in accordance to the direct impact model reported variously in the literature. The impact of chemically-induced, heterogeneous broadening of Raman and Dy3+ emission spectral bands is discussed on two examples from Mt. Malosa district, Malawi. A mean weighted U-Pb isotope age of 111 ± 1 Ma (pegmatitic-type) and a discordia age of 112 ± 1.6 Ma (hydrothermal-type) as obtained by LA-ICP-MS confirm their close genetic and temporal relationship. Studied zircon examples demonstrate that the amount of radiation damage present may have a substantial effect on the precision of LA-ICP-MS ages, but cannot be considered an exclusive cause for bias of obtained isotope ages. [ABSTRACT FROM AUTHOR]

Zirconolite‐rich full ceramic wasteforms designed to immobilize Pu‐bearing wastes were produced via hot isostatic pressing (HIP) using stainless steel (SS) and nickel (Ni) HIP canisters. A detailed profiling of the elemental compositions of the major and minor phases over the canister–wasteform interaction zone was performed using scanning electron microscopy combined with energy‐dispersive X‐ray spectroscopy (SEM‐EDS) characterization. Bulk sample analyses from regions near the center of the HIP canister were also conducted for both samples using X‐ray diffraction and SEM‐EDS. The sample with the Ni HIP canister showed almost no interaction zone with only minor diffusion of Ni from the inner wall of the canister into the near‐surface region of the wasteform. The sample with the SS HIP canister showed ∼100–120 μm of interaction zone dominated by high‐temperature Cr diffusion from canister materials to the wasteform with the Cr predominantly incorporated into the durable zirconolite phase. We also examined, for the first time, changes to the HIP canister wall thickness caused by HIPing and demonstrated that no canister wall thinning occurred. Instead, in the areas examined, the canister wall thickness was observed to increase (up to ∼20%) due to the compression occurring during the HIP cycle. Further, only sparse formation of (Cr, Mn)‐rich oxide particles were noted within the HIP canister inner wall area immediately adjacent to the ceramic material, with no evidence for reverse diffusion of ceramic materials. Though the HIP canister–wasteform interaction extends to ∼120 μm when using an SS HIP canister for the system investigated, this translates to <<1 vol.% for an industrial scale HIPed wasteform. Importantly, the HIP canister–wasteform interactions did not produce any obviously less durable phases in the wasteform or had any detrimental impact on the HIP canister properties. [ABSTRACT FROM AUTHOR]

Two new iso-structured uranyl oxide hydroxyl hydrate (UOH) phases with the incorporation of cobalt(ii) or nickel(ii) ions have been synthesised under hydrothermal conditions and structurally characterised. Both K4Co(OH)3(H2O)9[(UO2)12(O)7(OH)13] (1) and K4Ni(OH)3(H2O)9[(UO2)12(O)7(OH)13] (2) have two-dimensional (2D) polymeric uranyl oxohydroxyl layers with either potassium and hydroxyl cobalt(ii) (1) or potassium and hydroxyl nickel(ii) (2) ions between layers via uranyl–cation interactions. This work highlights the feasibility of making new UOH phases via a hydrothermal route at relatively higher solution pHs. It also demonstrates that other transition metal ions which are readily available in the environment may also be incorporated into such UOH phases during the natural weathering of uraninite as well as during the storage and disposal of spent nuclear fuels. [ABSTRACT FROM AUTHOR]

In the search for novel ceramics for use within nuclear fuel–related applications and nuclear waste-form matrices, a major focus has been on the development of radiation-tolerant materials. Of particular interest in this field have been numerous compounds with either pyrochlore or the related fluorite-type structures. In this study, we look to expand the family of compounds with defect fluorite–type structure. We have fabricated three new compounds; Yb2Sn1.125O5.25, Yb2Sn1.25O5.5, and Yb2Sn1.375O5.75. The compound Yb2Sn1.125O5.25 was determined, via x-ray diffraction, to have the long-range defect fluorite structure, Fm-3 m symmetry, with cell parameter a = 5.17233(1). Further to this, Sm2ZrO5 and Yb2TiO5 compounds were also fabricated and crystal structures characterised. The use of transmission electron microscopy has revealed a much more complex crystal structure than that of the relatively high symmetry fluorite, with the presence of structural modulations being detected. The ion-irradiation response of these compounds was tested via bulk specimen irradiation using 15-MeV gold ions with grazing incidence x-ray diffraction characterisation. The results show that both Sm2ZrO5 and Yb2Sn1.25O5.5 are highly tolerant to ion-irradiation exposure whilst Yb2TiO5 is susceptible to amorphisation. [ABSTRACT FROM AUTHOR]

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]

The structural effects of incorporating Cs into the monoclinic and tetragonal hollandites Ba1.2− x Cs x Mg1.2− x/2Ti6.8+ x/2O16 and Ba1.2− x Cs x Al2.4− x Ti5.6+ x O16 have been studied using powder neutron diffraction and 133Cs and 27Al MAS NMR. Addition of Cs to the monoclinic structure induces a ‘shear-type collapse’, in agreement with previously published results. NMR spectra show that the addition of Cs does not change the local structure around the Al cations within the tunnel walls. An algorithm is given that allows a prediction of unit cell parameters to be made for tetragonal hollandites containing barium. [ABSTRACT FROM AUTHOR]

Abstract: Time-of-flight powder neutron diffraction has been performed on oxides with composition (La1− x Nd x )2Zr2O7 and Nd2(Zr1− x Ti x )2O7, where , 0.2, 0.4,…1.0, in order to determine the solid solution behaviour across each series. Between La2Zr2O7 and Nd2Zr2O7, a cubic pyrochlore phase is observed (, ). A linear decrease in the lattice parameter from 10.8047 to 10.6758Å indicates complete miscibility of the two end-members. For the same series, the oxygen x-parameter increases from 0.3313 to 0.3348, suggesting increased distortion of the 6 coordinate B sites and reduced distortion of the 8 coordinate sites. There is limited solubility of Nd2Ti2O7 in Nd2Zr2O7. Exsolution of a monoclinic phase (, ) rich in Nd2Ti2O7 is observed at approximately . The compositional range over which a solid solution exists is more extensive than that which has been previously reported. The solubility of Nd2Zr2O7 in Nd2Ti2O7 is very low. [Copyright &y& Elsevier]

Fly ash from a coal-fired power plant was investigated to obtain detailed information on its physical and chemical properties, and to gain an understanding of potential environmental and health impacts associated with its disposal in landfills. The studied material was produced through combustion of Illinois Basin coal and trapped within the power plant by an electrostatic precipitator. It is a fine-grained, low-Ca fly ash containing primarily SiO[sub2], Al[sub2]O[sub3], and Fe[sub2]O[sub3], and is enriched in many toxic elements (e.g., Be, Zn, As, Cd, Tl, Pb, and U) by a factor of up to 30 relative to coal. The ash consists of mainly hematite, magnetite, mullite, quartz, and amorphous material. These constituents occur mostly as spherical particles with diameters of less than 13 µm. We examined the physical, chemical, and structural characteristics of individual fly ash particles by scanning and transmission electron microscopy and electron probe microanalysis. The results demonstrate that, with the exception of complex plerospheres, individual particles are chemically fairly homogeneous, but a pronounced compositional variation exists among particles with similar physical and structural attributes. Electron microprobe data document that several trace elements, including U, are partitioned into the Fetich particles. Transmission electron microscopy revealed that various types of small (<1 µm) crystalline Ca-rich phases, including lime, are attached to the glass spheres, particularly the non-magnetic glass. These crystals may contain substantial amounts of S. Even though only a few of these crystals were analyzed quantitatively, our data indicate that the Ca-rich and S-rich phases may be important hosts for trace elements such as V and Zn. The observed element partitioning and the existence of surface-attached crystals enriched in certain trace elements suggest that fly ash from coal-fired power plants might have a more deleterious environmental... [ABSTRACT FROM AUTHOR]

Presents a study which described the occurrence of oriented geikielite inclusions in magnesium-aluminum spinel. Analytical procedures; Description of geological setting; Discussion.

Presents a study which determined the hydroxide contents of spessartine-almandine garnets from pegmatites in the United States by infrared spectroscopy. Methods; Results; Discussion.

In developing improvements in nuclear fuels, work has been conducted in replacing boron with lanthanides to act as neutron absorbent materials. To further this development for the first time the three major polymorphs of Dy 2 TiO 5 have been fabricated as bulk, single-phase materials in a systematic study. Crystal structure refinement has been carried out from powder x-ray diffraction data, with further structural detail attained via electron diffraction. A cubic phase, defect-pyrochlore, Fd-3m space group, was found with cell parameter a = 10.2996 (1) Å and oxygen x48f positional parameter = 0.331 (1). Dy 2 TiO 5 was also fabricated as a bulk, single-phase compound with hexagonal symmetry, P6 3 /mmc space group, with cell parameters a = b = 3.6307(2), c = 11.8963(8) Å. The radiation response for each of the polymorphs has been investigated in-situ via 1 MeV Kr – ion-irradiation and transmission electron microscopy characterisation at the IVEM-TANDEM facility, Argonne National Laboratory. Critical temperatures, T c , for maintaining crystallinity during irradiation were determined and showed Dy 2 TiO 5 with either orthorhombic or cubic symmetry to perform the best, with the lowest T c values of 711 and 761 K respectively when compared with the hexagonal form. These relatively low T c values may be attributed to different characteristics for each phase; high anti-site defect formation energy for the orthorhombic symmetry, and the ability to accommodate disorder for the cubic symmetry. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The effects of irradiation on CaWO4, SrWO4, BaWO4, YVO4, LaVO4, YNbO4, and LaNbO4 were investigated on thin crystals using 1.0 MeV Kr ions at 50‐1000 K. All of the ABO4 compounds can be amorphized with calculated damage cross sections (σa = 1/Fc0) in the range of ~0.30‐1.09 × 10‐14 cm2 ion−1 at zero Kelvin. The analysis of fluence‐temperature data returned critical temperatures for amorphization (Tc) of 311 ± 1, 358 ± 90, 325 ± 19, 415 ± 17, 541 ± 6, 636 ± 26, and 1012 ± 1 K, respectively, for the compounds listed above. Compared with previous in situ irradiation of ABO4 orthophosphate samples using 0.8 MeV Kr ions, the Tc values of LaVO4 and YVO4 are higher than those of LaPO4 and YPO4 by 82 K and 124 K, respectively. The Tc values of the three scheelite structures, CaWO4, SrWO4, and BaWO4, indicate that they are the most radiation tolerant compounds under these conditions. The A‐B cation anti‐site energies, EfAB, determined by DFT range from 2.48 to 10.58 eV and are highly correlated with the A‐B cation ionic radius ratio, rA/rB, but are not correlated with Tc across the different structure types, suggesting that the formation and migration energies of Frenkel defects play a more important role in damage recovery in these compounds. We also discuss the role of cation and anion charge/iconicity as determined by DFT. ABO4 compounds with the zircon structure and B = P or V have a distinct advantage over those with B = Si as the damaged regions do not appear to be significantly affected by polymerization of (PO4)3− or (VO4)3− groups which might stabilize the amorphous fraction and ultimately lead to phase separation as observed in zircon (ZrSiO4). [ABSTRACT FROM AUTHOR]

New microsphere sorbents are reported, which could find application in demanding radiation environments and especially as targets for the production of nuclear medicines by neutron irradiation. An easily-synthesized Zr anionic complex was introduced into quaternary amine-functionalised polystyrene-divinylbenzene-based anion-exchange resins by batch adsorption. Upon carbothermal reduction, the precursors were converted to porous carbon matrices containing particles of ZrC and ZrO2 polymorphs. The most phase-pure material, ZrAX-1, possessed high surface area, multi-scale porosity and high mechanical strength. Adsorption of Re and W was investigated and its possible deployment as a reusable host for the production of 188W/188Re is discussed. [ABSTRACT FROM AUTHOR]

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 P3̅m1 space group. Raman characterization revealed the typical vibration modes for the uranyl units with the calculated U=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. [ABSTRACT FROM AUTHOR]

The preparation, characteristics and adsorption properties of novel porous carbon-ceramic composite microspheres are presented. The composites were synthesised by a simple ion exchange process involving the cationic Zr tetramer and commonly-available macroporous sulphonated polystyrene-divinylbenzene cation exchange resins, with subsequent carbothermal reduction at 1350 °C. The materials were extensively characterised with respect to composition, chemical structure and porosity. Carbothermal reduction of the Zr-loaded templates resulted in formation of crystallites of the MAX phase zirconium sulphide carbide (Zr 2 SC) embedded within a highly microporous carbon framework with a macroporous secondary structure inherited from the resin template. Despite the high BET surface areas of the Zr 2 SC-carbon composite microspheres (in some cases, greater than 600 m 2 g −1 ), they are extremely mechanically robust. The microspheres displayed high adsorption selectivity for oxoanions relative to cationic solution species, including perrhenate (ReO 4 − ), a pertechnetate (TcO 4 − ) surrogate. Accumulation of ReO 4 − on the Zr 2 SC particles was unequivocally demonstrated by elemental mapping. Such materials are potential candidates as combined 99 Tc sorbents and reusable transmutation hosts. [ABSTRACT FROM AUTHOR]

In situ neutron powder diffraction experiments are applied to physical, kinetic, and microstructural characterization of uranium mononitride as a promising light water reactor fuel material. The temperature-variable coefficient of thermal expansion and isotropic Debye Waller factors are obtained by sequential Rietveld refinement over 499–1873 K. Oxidation of a UN pellet (95.2% density) under flow of 11 mg/min D 2 O is observed to initiate above 623 K and the rate increases by a factor of approximately 10 from 673 to 773 K, with activation energy 50.6 ± 1.3 kJ/mol; uranium oxide is the only solid corrosion product. [ABSTRACT FROM AUTHOR]

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]

A method to produce picolinate ligand in situ under hydrothermal conditions has been used to synthesize four uranyl hydroxyl, oxo- and oxohydroxyl picolinato complexes. (UO 2 )(OH)(Pic) ( 1 ) (HPic = picolinic acid) contains 7-fold coordinated uranyl hydroxyl dimers linked through μ 2 -bridging Pic ligands forming a one-dimensional (1D) polymer. (NH 4 )[(UO 2 ) 3 (O) 2 (OH)(Pic) 2 ] ( 2 ) consists of 7-fold coordinated uranyl oxohydroxyl trinuclear units linked through both μ 2 - and μ 3 -Pic ligands forming a 1D polymer. (NH 4 )[(UO 2 ) 2 (O) 2 (Pic)] ( 3 ) is constructed with 7-fold coordinated uranyl oxo-dinuclear units linked through oxo- and μ 3 -Pic ligands forming a 1D polymer. (NH 4 )[(UO 2 ) 4 (O) 2 (OH) 2 (Pic) 2 (INT)]·H 2 O ( 4 ) (HINT = isonicotinic acid) is made of 7-fold coordinated uranyl oxohydroxyl tetranuclear units linked through both Pic and INT ligands forming a 1D polymer. All four polymers are thermal robust to 350 °C. Raman spectroscopy confirmed the presence of uranyl ion and Pic ligand. In addition, red enhanced fluorescence emissions have been observed for both 1 and 4 . The synthesis method, with the advantage of controlling uranyl hydrolysis and generating ligand in situ , provides a more reliable way to make new coordination polymers of carboxylate ligands with various uranyl hydrolysis species. [ABSTRACT FROM AUTHOR]

3C-β SiC was implanted with He and H ions using plasma immersion ion implantation (PIII). Regions of damage were created at various depths by applying a sample stage bias of 5 kV, 10 kV, 20 kV or 30 kV. Raman spectroscopy results indicate that He irradiation leads to more damage compared to H irradiation, as observed via increased disordered C and Si signals, as well as broadening of the SiC peaks. X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure spectroscopy (NEXAFS) results indicate significant change to the SiC structure and that surface oxidation has occurred following irradiation, with the degree of change varying dependent on impinging He fluence. The distributions of implanted species were measured using elastic recoil detection analysis. Despite the varying degree and depth of damage created in the SiC by the He ion irradiations, the retained H distribution was observed to not be affected by preceding He implantation. [ABSTRACT FROM AUTHOR]

With the coordination of dimethylformamide (DMF), two new uranium(VI) complexes with either 4-hydroxybenzoic acid (H 2 phb) or terephthalic acid (H 2 tph) have been synthesized under solvothermal conditions and structurally characterized. [(UO 2 ) 2 (Hphb) 2 (phb)(DMF)(H 2 O) 3 ]·4H 2 O ( 1 ) has a dinuclear structure constructed with both pentagonal and hexagonal bipyramidal uranium polyhedra linked through a µ 2 -bridging ligand via both chelating carboxylate arm and alcohol oxygen bonding, first observation of such a coordination mode of 4-hydroxybenzoate for 5 f ions. [(UO 2 )(tph)(DMF)] ( 2 ) has a three-dimensional (3D) framework built with pentagonal bipyramidal uranium polyhedra linked with µ 4 -terephthalate ligands. The 3D channeled structure is facilitated by the unique carboxylate bonding with nearly linear C–O–U angles and the coordination of DMF molecules. The presence of phb ligands in different coordination modes, uranyl ions in diverse environments and DMF in complex 1 , and tph ligand, DMF and uranyl ion in complex 2 has been confirmed by Raman spectroscopy. In addition, their thermal stability and photoluminescence properties have been investigated. [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]

The preparation of hierarchically porous phase-pure carbon–zirconium carbide spheres with surface areas upwards of 70 m 2 /g and diameters in the 1–2 mm range has been achieved. The zirconium carbide beads were prepared through carbothermal reduction of polyacrylonitrile-zirconium composites prepared via three different routes including infiltration of a zirconium precursor into preformed polyacrylonitrile (PAN) beads and two one-pot co-precipitation methods. Depending on the route used to prepare the composites, relatively high surface area phase-pure zirconium carbides with the radial macroporous internal structure of the PAN template could be prepared. The adsorption of the elements U, Mo, Cs and Sr by the zirconium carbide beads was studied as a function of pH in the range 1–13 and target element concentrations of 0.025 mmol/L. The as-prepared hierarchical zirconium carbide beads demonstrated almost quantitative uptake of Mo below pH 4 with uptake decreasing to close to zero and above pH 10.5. On the other hand, U uptake was negligible below pH 4 and became quantitative in the range 4–12. Cesium was not extracted to any significant extent in the pH range studied and Sr only to a limited extent above pH 10. The engineered hierarchical porosities, neutron transparency, thermal stability and anticipated chemical stability of the present zirconium carbide spheres makes them promising candidates as reusable transmutation targets for Minor Actinide incineration. [ABSTRACT FROM AUTHOR]

Garnets have been considered as host phases for the safe immobilisation of high-level nuclear waste, as they have been shown to accommodate a wide range of elements across three different cation sites, such as Ca, Y, Mn on the a-site, Fe, Al, U, Zr, and Ti on the b-site, and Si, Fe, Al on the c-site. Garnets, due to their ability to have variable composition, make ideal model materials for the examination of radiation damage and recovery in nuclear materials, including as potential waste forms. Kimzeyite, Ca 3 Zr 2 FeAlSiO 12 , has been shown naturally to contain up to 30 wt% Zr, and has previously been examined to elucidate both the structure and ordering within the lattice. This study examines the effects of radiation damage and recovery using in-situ ion beam irradiation with 1 MeV Kr ions at the IVEM-TANDEM facility, Argonne National Laboratory. The complementary Hf containing system Ca 3 Hf 2 FeAlSiO 12 was also examined, and found to have a different response to irradiation damage. A sample of irradiated Ca 3 Zr 2 FeAlSiO 12 , at 1000 K, was characterised using aberration corrected (S)TEM and found to contain discreet, nano-sized, crystalline Fe rich particles, indicating a competing process during recovery is occurring. [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]

Using transmission electron microscopy we show that planar deformation lamellae occur within quartz in the substrate of a rock fulgurite, i.e., a lightning-derived glass. These lamellae exist only in a narrow zone adjacent to the quartz/fulgurite boundary and are comparable to planar deformation features ("shock lamellae") caused by hypervelocity impacts of extra-terrestrial objects. Our observations strongly suggest that the lamellae described here have been formed as a result of the fulgurite-producing lightning strike. This event must have generated a transient pressure pulse, whose magnitude, however, is uncertain at this stage. [ABSTRACT FROM AUTHOR]

Great effort has been made to synthesize larger uranyl peroxide clusters whilst the understanding of the basic construction units for these clusters still needs to be further explored. Two small uranyl peroxide clusters stabilized by simple dicarboxylate ligands have been synthesized and characterized. Na 10 [(UO 2 )(O 2 )(C 3 H 2 O 4 )] 5 ·20H 2 O ( 1 ) has a pentagonal ring stabilized by malonate and [Na 4 K 2 (UO 2 ) 2 (O 2 )(C 2 O 4 ) 4 ]·6H 2 O ( 2 ) has a dimer stabilized by oxalate. Cation-cation interactions between uranyl and alkali metal ions exist in both 1 and 2 , leading to the observation of elongated U O −yl bonds. Vibrational modes of uranyl ion, peroxide and malonate/oxalate ligands have been confirmed by Raman spectroscopy. The presence of malonate ligands prevents the pentagonal uranyl peroxide rings further assembling into larger clusters whilst the excess oxalate ligands inhibit the dimers further linking to nearby uranyl centers. [ABSTRACT FROM AUTHOR]

Three new coordination polymers of uranium(VI) with pyromellitic acid (H 4 btca) have been synthesized and structurally characterized. (ED)[(UO 2 )(btca)]·(DMSO)·3H 2 O ( 1 ) (ED=ethylenediammonium; DMSO=dimethylsulfoxide) has a lamellar structure with intercalation of ED and DMSO. (NH 4 ) 2 [(UO 2 ) 6 O 2 (OH) 6 (btca)]·~6H 2 O ( 2 ) has a 3D framework built from 7-fold coordinated uranyl trinuclear units and btca ligands with 1D diamond-shaped channels (~8.5 Å×~8.6 Å). [(UO 2 ) 2 (H 2 O)(btca)]·4H 2 O ( 3 ) has a 3D network constructed by two types of 7-fold coordinated uranium polyhedron. The unique μ 5 -coordination mode of btca in 3 enables the formation of 1D olive-shaped large channels (~4.5 Å×~19 Å). Vibrational modes, thermal stabilities and fluorescence properties have been investigated. [ABSTRACT FROM AUTHOR]

The reaction of uranium(VI) or thorium(IV) nitrate with p -toluenesulfonic acid (PTSA) in aqueous solutions at room temperature led to the formation of U(VI)/Th(IV) coordination polymers (CPs) with deprotonated μ 2 -bridging PTS anions. Both [(UO 2 )(PTS) 2 (PTSA)]·4H 2 O ( 1 ) and Th(PTS) 4 (H 2 O) 3 ( 2 ) have one-dimensional (1D) undulating polymeric structures built with pentagonal bipyramidal uranyl polyhedrons and 9-fold coordinated thorium polyhedrons, respectively, linked through μ 2 -bridging PTS anions. Both CPs have similar thermal decomposition patterns as they have similar structural type in the presence of the same ligand. Vibrational modes have been investigated and the structural features have been discussed together with relevant structures. [ABSTRACT FROM AUTHOR]