Search

Boric acid is a significant radioactive waste generated during the operation of nuclear power plants. Cementitious materials have been widely studied for the immobilization of boric acid. The generally used natural boric acid has been replaced by enriched boric acid for geochemical reasons and are expected to have varied behaviors in cementitious matrices. Results showed that simulated enriched/natural boric acid liquid wastes mostly contain boron in $${\mathrm{B}(\mathrm{OH})}_{4}^{-}$$ B ( OH ) 4 - and $${{\mathrm{B}}_{5}{\mathrm{O}}_{6}(\mathrm{OH})}_{4}^{-}$$ B 5 O 6 ( OH ) 4 - ionic forms, but the mass ratio of these species is higher in enriched boric acid solutions. In function with the concentration of enriched/natural boric acid, the solidified cementitious materials show different mineralogy.

In this report, we have systematically evaluated the role of boron in regulating the degradation, apatite formation and antibacterial properties of bioactive glasses by substituting SiO2 with B2O3 in S53P4 based glass composition. The structural analysis of the glasses has been carried out using neutron diffraction and Raman spectroscopic techniques. The structural analysis of S53P4 base glass has revealed the presence of silicate and phosphate units in the form of Q2Si, Q3Si and isolated Q0P units. With the increasing replacement of SiO2 with B2O3, Raman spectroscopy revealed the formation of non-ring metaborate units and borate rings consisting of both BO3 and BO4 units at the expense of Q2Si and Q3Si units. Furthermore, DSC, HSM and dilatometry results confirmed that the sinterability parameter (Sc) and fragility index (m) values of borosilicate bioactive glasses help in achieving superior sintering and thermal processing without devitrification. Additionally, in vitro SBF immersion studies revealed an accelerated release of Si4+ and Ca2+ ions from the borosilicate glasses. In vitro antibacterial assays against E.coli bacterial inoculum illustrate the critical role of B2O3 in the bioactive glass composition.

The presence of lanthanide-tellurite "anti-glass" nanocrystalline phases not only affects the transparency in glass-ceramics (GCs) but also influences the emission of a dopant ion. Therefore, a methodical understanding of the crystal growth mechanism and local site symmetry of doped luminescent ions when embedded into the precipitated "anti-glass" phase is crucial, which unfolds the practical applications of GCs. Here, we examined the Ln

xLi2O–(100 − x)TeO2 (x = 20 and 25 mol%) and xV2O5–(25 − x)Li2O–75TeO2 (x = 1, 2, 3, 4 and 5 mol%) glasses were prepared by melt-quenching and their thermal and structural properties were characterized by differential scanning calorimetry, Raman spectroscopy, high-energy X-ray diffraction and neutron diffraction and reverse Monte Carlo (RMC) simulations. The glass transition temperature increases steadily with an increase in V2O5 mol% in lithium tellurite glasses due to an increase in the average single bond energy of the glass network. The X-ray and neutron diffraction structure factors were modelled by RMC technique and the Te–O distributions show the first peak in the range 1.85–1.90 Å, with V–O = 1.75–1.95 Å, Li–O = 1.85–2.15 Å and O–O = 2.70–2.80 Å. The average Te–O coordination number decreases with an increase in Li2O mol% in lithium tellurite glasses, and the V—O coordination decreases from 5.12 to 3.81 with an increase in V2O5 concentration in vanadium lithium tellurite glasses. The O–Te–O, O–V–O, O–Li–O and O–O–O linkages have maxima in the ranges 86°–89°, 82°–87°, 80°–85° and at 59o, respectively. The structural analysis of tellurite glasses reveal significant short-range and medium-range disorder due to the existence of a wide range of Te–O and Te–Te distances in the first coordination shell.

Nanoparticles of xRe2O3 – (100-x)CaWO4 (Re = Eu, Dy, Sm; x = 0, 1, 3, 5, 7 and 10 mol%) were synthesized by solid-state sintering at two annealing temperatures of 800 °C and 1150 °C and characterized by neutron diffraction, Raman and photoluminescence (PL) spectroscopy. The samples are composite materials and contain tetragonal CaWO4 and cubic Re2O3 phases. The unit cell parameters, atomic position co-ordinates, crystallite size, mole-fraction of phases, bond-lengths, bond-angles and cation-oxygen co-ordination numbers were determined by Rietveld analysis of the neutron diffraction data. The short-range structure of CaWO4 consists of snub disphenoid deltahedral CaO8 and tetrahedral WO4 units and the structure of cubic Re2O3 consists of two types of ReO6 units. All the W–O bonds in WO4 units are of equal lengths (1.77–1.79 A) whereas two kinds of slightly different Ca–O bond-lengths (2.41–2.45 A and 2.45–2.47 A) exist in CaO8 units. The neutron pair distribution function of the undoped CaWO4 samples shows the first peak in the range of 1.71–1.74 A due to W–O bonds and the second peak at 2.84 A due to O–O and Ca–O pair correlations. Raman studies of Eu-doped samples show only W–O vibration modes, however, Sm and Dy-doped CaWO4 show weak Raman peaks of Sm2O3 and Dy2O3, along with W–O bond vibrations. PL studies show highest orange-red emission at 1 mol% Sm2O3, green emission at 1 mol% Dy2O3 and red emission at 3 mol% Eu2O3. The light emission intensity in all the samples increases with the increase in annealing temperature from 800 °C to 1150 °C.

Neutron diffraction studies were performed on xSrO-(100-x)TeO2 (x = 5, 7.5 and 10 mol%) glass, anti-glass and crystalline samples. For the structural modeling, Fourier transformation, Reverse Monte...

Ca- and P-based bioactive glasses are excellent candidates for design and manufacture of biomaterials. Understanding the structure and physico-chemical–thermal behaviour of bioactive glasses is a fundamental step towards the design of a new generation of biocompatible materials. In this study, the structure of SiO2–CaO–Na2O glasses and its derivatives, obtained by substituting Na2O with P2O5 and prepared by melt–quench technique, was studied with neutron and electron diffraction techniques combined with thermal analysis, high-resolution electron microscopy and X-ray photoelectron spectroscopy. Neutron and electron diffraction data were analysed with reverse Monte Carlo simulation and pair distribution function analysis, respectively. Bioactivity of P2O5 substituted glasses was also investigated and proven in vitro using simulated body fluid. Based on the structural analysis, it was found that Si and P atoms are in well-defined tetrahedral units with a bond distance of 1.60 Å for both Si–O and P–O bonds, although P exhibits a higher average coordination number than Si. With increasing phosphate content, tendentious changes in the glass behaviour were observed. Linear increase in Tg, supported by the changes in the average coordination numbers of Si and P, indicates strengthening of network structure with increasing P content and formation of P–O–Ca atomic linkages, which lead to Ca–P-rich atomic environments in the silicate network. These Ca–P-rich environments trap volatile elements and thus decrease the total weight loss during heating at higher P concentrations. In the case of the highest investigated P2O5 content (5 mol%), nanoscale structural inhomogeneity and the formation of Ca–P-rich clusters were also revealed by electron diffraction and atomic resolution imaging. This type of Ca–(Na)–P clustering has a key role in the behaviour of phosphate-substituted silicate glasses under physiological conditions.

Reverse Monte Carlo (RMC) simulations were applied for modelling the atomic structure of the PbO-TeO2 glasses containing 10, 15 and 20-mol% PbO. The short-range order of the lead-tellurium-oxygen network, involving pair correlation functions of Pb O, Te O and O O pairs, the average coordination numbers and the three-particle bond-angle distributions were determined by the RMC analysis. The average Pb O coordination is in the range of 5.66 ± 0.19 to 6.02 ± 0.30, whereas Te O coordination (NTe-O) decreases steadily from 3.55 ± 0.04 to 3.36 ± 0.03 with increase in PbO concentration from 10 to 20 mol%. Raman studies also confirmed that NTe-O decreases on increasing PbO concentration, the latter acts as a modifier and disrupts the local tellurite speciation. The structural parameters are used in the Zwanziger model of stress-optic response to predict that PbO-TeO2 glasses should exhibit negative stress birefringence, a result which is in agreement with the experimental findings reported in the literature.

The partial, total and average coordination number of atoms and, their neighbor distributions have been determined by the neutron diffraction method and application of the Reverse Monte Carlo modeling for experimental data in As40Se60, As40Se30S30 and As40Se30Te30 chalcogenide glasses. The total coordination number of the arsenic and chalcogen atoms is 3 and 2 for all compounds. The average coordination number is 2.4, i.e. the 8-N rule is performed and main structural element is AsSe3 type pyramids, where depending on the chemical composition Se atom is replaced by S or Te atoms. The proportion of homopolar bonds is significant in As40Se60 and As40Se30S30 compositions, but sharply decreases in As40Se30Te30. In all compositions the neighbor distances between arsenic and selenium atoms are the same within error: 2.35 A (Se Se); 2.45 A (As As) and 2.40 A (As Se). The existence of medium range order (MRO) is proved by the analysis of the total and partial pair structural factors and correlation functions in above mentioned compositions. The geometric dimensions of the MRO area, i.e. the quasi-periodicity of density fluctuations in the MRO area and the size of nano-voids have determined within Elliott's void-based model. The change of the optical parameters by variation of the chemical composition has been established from the analysis of the optical transmission spectra.

After some decades in applying boric acid with natural isotopic abundance (natural boric acid, NBA) solution as a neutron absorber, some nuclear facilities have started to use boric acid enriched in B-10 (enriched boric acid, EBA) to increase the control ability and parallelly, decrease the amount of liquid waste. Meanwhile, the stabilization condition of EBA in the cementitious matrix and durability of the waste form in disposal facilities have not been assessed or at least have not been reported yet. However, high relative mass difference between the two stable isotopes of boron (B-10 and B-11) implies a different leachability index for cementitious matrix prepared with NBA and EBA wastes.In this study, the leachability (ASTM C1308-08 standard, 2017) of boron isotopes from cementitious matrix and its geochemical background will be assessed using ICP-OES, XRD, SEM-EDX and Raman-spectroscopy. The effects of parameters such as temperature, water to cement ratio (w/c), boric acid concentration and shape of the waste form will be studied. Geochemical modeling of the experiments will be done via PHREEQC software, which should support our understanding of the different geochemical behavior of NBA and EBA.Based on the theoretical knowledge, a significant increase in leachability of boron from the cementitious matrix is expected when EBA is used instead of NBA because of the geochemical behavior of the two stable isotopes. Increase in leachability is expected when temperature and w/c increased, whereas the leachability will decrease when the normal cylindrical shape of samples are changed to spherical shape.References:M. Saleh and H. A. Shatta; 2013; Immobilization of Simulated Borate Radioactive Waste Solution in Cement-Poly(methylmethacrylate) Composite:Mechanical and Chemical Characterizations; Journal of Nuclear Chemistry; Article ID 749505. Lucile Dezerald, Jorge J. Kohanoff, Alfredo A. Correa, Alfredo Caro, Roland J.-M. Pellenq, Franz J. Ulm and Andrés Saúl; 2015; Cement as a Waste Form for Nuclear Fission Products: The Case of 90Sr and Its Daughters; Journal of Environmental science and technology; 49; 13676−13683. ASTM C1308 - 08(2017); Standard Test Method for Accelerated Leach Test for Diffusive Releases from Solidified Waste and a Computer Program to Model Diffusive, Fractional Leaching from Cylindrical Waste Forms; west conshohocken, PA 19428, United state IAEA; 1996; Processing of nuclear power plant waste streams containing boric acid; IAEA-TECDOC-911, ISSN 1011-4289; Vienna, Austria.

Thin films of GexSb40-xSe60 (x = 15, 20, 25, 27, 32 and 35 at.%) were deposited on quartz by vacuum thermal evaporation of the pre-synthesized parental glasses powders. By spectroscopic ellipsometry the complex refractive index values are determined in the 0.20–33 μm spectral range. The optical band gap and single oscillator energies are established as a function of the Ge content and average coordination number Z. In the (0.85–3.5) μm spectral range the GexSb40-xSe60 films possess about 80% transmission. Infrared ellipsometric and Raman studies identified Se Se and Ge Ge homopolar bonds, oxygen and hydrogen related impurity bonds and heteropolar Ge Se and Sb Se chemical bonds. Neutron- and X-ray Diffraction data coupled with Reverse Monte Carlo simulations support the optical results reproducing the Ge Se and Sb Se cell units and cross-linked Ge Ge bonds. Atomic force microscopic imaging confirmed smooth surfaces with low RMS roughness values (

The structure of WO3-TeO2 glasses containing 15, 20 and 25 mol% WO3 are studied by neutron diffraction (ND), high energy X-ray diffraction (XRD) and X-ray Absorption Near Edge spectroscopy (XANES). The short-range structural properties of glasses i.e. Te O and W O speciation, coordination number distributions, bond-lengths, and the O Te O, O W O and O O O bond angle distributions in the glass network are determined by the Reverse Monte Carlo (RMC) simulations of the ND and XRD data. RMC technique successfully determined all partial pair correlation functions and the coordination number distributions revealed that glass network consists predominantly of TeO4 and WO4 units with small amounts of triangular, penta and hexa co-ordinated units. The average W O and Te O bond lengths are in the ranges: 1.69–1.75 ± 0.01 A and 1.99–2.00 ± 0.01 A respectively. Both W O and Te O correlation peaks are asymmetrical, that indicate a distribution of their bond lengths in the respective structural units. The O-Te-O bond angle distribution has a peak at 107 ± 2°. Similarly the O-W-O bond angle distribution has a peak at 108 ± 5°. On increasing the WO3 concentration from 15 to 25 mol%, the average Te O coordination number decreases from 3.80 to 3.61 ± 0.02 due to the structural transformation: TeO4 → TeO3, similarly the W O coordination also decreases and is in the range: 3.79–3.67 ± 0.02. XANES studies found that the oxidation state of Te and W ions in the glasses are 4+ and 6+ respectively.

In this work, following our previous work on molybdate glasses, we employ a combination of neutron diffraction and neutron Compton scattering, augmented by ab initio harmonic lattice dynamics and Reverse Monte Carlo modelling to characterise the force-constant disorder in the tungsten oxide-based glasses. Specifically, we discuss the correlations between the average interatomic force constant magnitudes inferred from neutron Compton scattering and the glass formation ability, measured in terms of the value of the glass transition temperature, as well as the average bond-lengths and interatomic distances obtained from diffraction data analysis. Moreover, we provide a comparative analysis of the widths of force-constant distributions of individual atomic species in glasses and their precursor metal oxides based on the distributions of the widths of nuclear momentum distributions. Furthermore, we assess the degree of softening of atom-projected vibrational densities of states induced by the force-constant disorder in the glasses.

The local structures of amorphous As40Se60, As40Se30S30, As33.3Se33.3S33.4 chalcogenide glass semiconductors have been studied by neutron diffraction and Raman scattering methods. The neutron diffraction data-sets were modeled by Reverse Monte Carlo (RMC) simulation technique. Several first and second neighbour distances, coordination numbers and bond-angle distributions have been calculated. It is established that the first neighbour atomic distances are overlapping at three characteristic distances, namely the S S and Se S are centered at 2.2(5) A, while the As S and Se Se are centered at 2.35 A, the As As and As Se are centered at 2.4(5) A. The average coordination numbers in As40Se60 (ZAs = 3.03; ZSe = 2.02) and As40Se30S30 (ZAs = 3; ZSe = 2.07; ZS = 2) compositions were determined and found to be consistent with, “8-N” rule. The slight deviations from this rule is discovered in case of As33.3Se33.3S33.4 (ZAs = 3.07; ZSe = 2.09; ZS = 1.95) composition. The main role in the formation of medium range order belongs to Se Se bonds. It has been identified that the replacement of Se with S atoms causes a slight change in coordination numbers. The similarity of θSe As Se and θAs Se As bond angle distributions suggest that S atoms have a similar role in the structure formation as Se atoms. The RMC models highlighted a glassy network built-up from AsSe3 trigonal bipyramids, in all binary and ternary samples.

[EN] Exploring the reasons for the initiation of Al-O-Al bond formation in alkali-earth alumino silicate glasses is a key topic in the glass-science community. Evidence for the formation of Al-O-Al and Al-NBO bonds in the glass composition 38.7CaO-9.7MgO-12.9AlO-38.7SiO (CMAS, mol%) has been provided based on Molecular Dynamics (MD) simulations. Analyses in the short-range order confirm that silicon and the majority of aluminium cations form regular tetrahedra. Well-separated homonuclear (Si-O-Si) and heteronuclear (Si-O-Al) cluster regions have been identified. In addition, a channel region (C-Region), separated from the network region, enriched with both NBO and non-framework modifier cations, has also been identified. These findings are in support of the previously proposed extended modified random network (EMRN) model for aluminosilicate glasses. A detailed analysis of the structural distributions revealed that a majority of Al, 51.6%, is found in Si-O-Al links. Although the formation of Al-O-Al and Al-NBO bonds is energetically less favourable, a significant amount of Al is found in Al-O-Al links (33.5%), violating Lowenstein's rule, and the remainder is bonded with non-bridging oxygen (NBO) in the form of Al-NBO (Al-O-(Ca, Mg)). The conditions necessary for the formation of less favourable bonds are attributed to the presence of a high amount of modifier cations in current CMAS glass and their preferable coordination., A. R. A. and S. B. would like to thank Dr Muraleedharan K., Director, CSIR-CGCRI for his strong support and encouragement. A. R. A. gratefully acknowledges the financial support of the Budapest Neutron Centre, Hungary, for allotting beam time and financial support (BRR_407) under the NMI3-II program. Part of this work was developed in the scope of the CICECO-Aveiro Institute of Materials (UID/CTM/50011/2013) project, and funded by FEDER funds through the Operational Programme Competitiveness Factors (COMPETE 2020) and the Portuguese Foundation for Science and Technology (FCT). S. G. would like to thank the German Research Foundation (DFG) for financial support through the priority program SPP 1594 ‘‘Topological Engineering of Ultra-Strong Glasses’’ (project BI1453/1-2). Simulations were performed with computing resources granted by RWTH Aachen University under project rwth0297.

The short- and medium-range order of glassy MoO 3 –ZnO–B 2 O 3 has been studied by neutron diffraction and reverse Monte Carlo simulation. The partial atomic pair correlation functions and coordination numbers are presented, not yet reported for this system. We have established that the first neighbour distances do not depend on concentration within limit of error, the actual values are r B–O = 1.38 A, r Mo– O = 1.72 A and r Zn–O = 1.97 A. It is found that ZnO takes part in the glassy structure as network former, ZnO 4 tetrahedral are linked both to MoO 4 and to BO 3 &BO 4 groups. It is revealed that BO 4 /BO 3 increases with increasing B 2 O 3 content. We have found that only small amount of boroxol ring is present, BO 3 and BO 4 groups are organized into superstructure units, and a small part is in isolated BO 3 triangles The BO 3 and BO 4 units are linked to MoO 4 or ZnO 4 , forming mixed [4] Mo–O– [3, 4] B, [4] Mo–O– [4] Zn, [3, 4] B–O– [4] Zn bond-linkages.

Neutron Compton scattering and neutron diffraction, augmented by ab initio modelling, have been applied for the characterisation of disorder in molybdate glasses, 20MoO3 + 30Nd2O3 + 50B2O3, 40MoO3 + 30Nd2O3 + 30B2O3, and 50MoO3 + 25Nd2O3 + 25B2O3, along with their parent metal oxides, B2O3, MoO3 and Nd2O3. Softening of the atom-projected vibrational densities of states (apVDOSes) was observed for all constituent nuclei in the metal oxide systems, with respect to the ab initio harmonic lattice dynamics predictions. For the oxygen, the mode softening was attributed to force-constant disorder, and for the boron to the isotopic mass disorder. A universal scale of disorder in oxide glasses has been proposed. The scale relies on the assumption that the amount of disorder-induced phonon softening can be bracketed by two extreme situations: (i) a completely disordered system with no confining potential whose momentum distribution is described by the Maxwell-Boltzmann momentum, and (ii) the compositional average of harmonic lattice dynamics predictions for individual metal oxide systems. The highest degree of disorder on this scale was observed for the boron in the molybdate glasses with the highest amount of B2O3. The distributions of total (summed over all nuclei) effective force constants were found to be at least an order of magnitude wider than their counterparts calculated for the parent metal oxide systems, indicating a much greater degree of positional disorder-induced force constant disorder in the molybdate glasses. The sum of all mean effective forces acting on all constituent nuclei in the molybdates was found to be decreasing with the increasing amount of the glass-former B2O3, clearly showing a systematic softening of the structure of the glasses. The biggest contributions to the total average effective mean force in all three molybdates were found for the molybdenum and neodymium.

Aluminosilicate glasses are considered to follow the Al-avoidance principle, which states that Al–O–Al linkages are energetically less favorable, such that, if there is a possibility for Si–O–Al linkages to occur in a glass composition, Al–O–Al linkages are not formed. The current paper shows that breaching of the Al-avoidance principle is essential for understanding the distribution of network-forming AlO4 and SiO4 structural units in alkaline-earth aluminosilicate glasses. The present study proposes a new modified random network (NMRN) model, which accepts Al–O–Al linkages for aluminosilicate glasses. The NMRN model consists of two regions, a network structure region (NS-Region) composed of well-separated homonuclear and heteronuclear framework species and a channel region (C-Region) of nonbridging oxygens (NBOs) and nonframework cations. The NMRN model accounts for the structural changes and devitrification behavior of aluminosilicate glasses. A parent Ca- and Al-rich melilite-based CaO–MgO–Al2O3–SiO2 ...

Advances in condensed matter physics 2018, 7158079 (2018). doi:10.1155/2018/7158079, Glasses with composition of Ge$_x$Sb$_{40-x}$Se$_{60}$ (x= 40, 35,32, 27, 20, 15 at. %) have beensynthesized. Neutronand X-ray diffraction techniques were used to study the atomic glassy structure,and Reverse Monte Carlo(RMC) simulations were applied to model the 3-dimensional atomic configurations and thorough mapping of the atomic parameters, such as first and second neighbour distances, coordination numbers, and bond-angle distributions. The results are explained with formation of GeSe$_4$ and SbSe$_3$ structural units, which correlate with the Ge/Sb ratio. For all the studied compositions, the Ge-Se, Sb-Se, Ge-Ge, and Se-Se bonds are significant. RMC simulations reveal the presence of Ge-Sb and Sb-Sb bonds, being dependent on Ge/Sb ratio. All atomic compositions satisfy formal valence requirements, i.e., Ge is fourfold coordinated, Sb is threefold coordinated, and Se is twofold coordinated. By increasing the Sb content, both the Se-Ge-Se bonds angle of 107±3° and Se-Sb-Se bonds angle of 118±3° decrease, respectively, indicating distortion of the structural units. Far infrared Fourier Transform spectroscopic measurements conducted in the range of 50-450 vm$^{-1}$ at oblique (75°) incidence radiation have revealed clear dependences of the IR band’s shift and intensity on the glassy composition, showing features around x=27 at.% supporting the topological phase transition to a stable rigid network consisting mainly of SbSe$_3$ pyramidal and GeSe$_4$ tetrahedral clusters. These results are in agreement with the Reverse Monte Carlo models, which define the Ge and Sb environment., Published by Hindawi Publ. Corp., New York, NY ˜[u.a.]œ

We present an overview of ongoing developments in epithermal neutron spectroscopy using the VESUVIO+ beam line at the ISIS Facility. In its current incarnation, VESUVIO+ provides a suitable platform for further and much-needed progress in the judicious exploitation of epithermal neutrons at a pulsed spallation source, as well as constitutes a necessary milestone towards a next-generation station for Epithermal and Thermal Neutron Analysis, hereafter ETNA. In particular, we discuss recent improvements in capability relative to its predecessor VESUVIO. These include the concurrent use of mass-resolved neutron spectroscopy, transmission, and diffraction to explore the properties of complex functional materials, as well as the implementation of techniques unique to pulsed neutron sources such as γ-ray dopplerimetry and energy-resolved prompt-γ activation analysis.

Argillaceous rocks are considered as suitable host rock formation to isolate the high-level radioactive waste from the biosphere for thousands of years. Boda Claystone Formation, the possible host rock formation for the Hungarian high-level radioactive waste repository, has geologically and mineralogically been studied in detail, but its physico-chemical parameters describing the retention capability of the rock needed further examinations. Studies were performed on thin sections subjected to 72 h sorption experiments using inactive Nd(III). Nd(III) has been used as a chemical analogue for transuranium elements of the radioactive waste to examine the ion uptake capability of the micrometre size mineral phases occurring in the rock. The elemental mapping of synchrotron radiation-based microscopic X-ray fluorescence (micro-XRF) combined with scanning electron microscopy energy dispersive X-ray analysis (SEM/EDX) has sufficient sensitivity to study the uptake capability of the different mineral phases on the microscale without the necessity of applying radioactive substances. Elemental maps were recorded on several thousand pixels using micrometre magnitude spatial resolution. By interleaving micro-XRF and SEM/EDX data sets from the same sample area and applying multivariate methods, calcite and clay minerals could be identified as the main mineral phases responsible for Nd(III) uptake without using additional microscopic X-ray diffraction mapping. It should be highlighted that the ion uptake capability of dolomite containing calcium and magnesium could be distinguished from the characteristics of calcite only by the interleaving of micro-XRF and SEM/EDX data sets. The presence of minerals was verified by applying microscopic X-ray diffraction point measurements. Copyright © 2015 John Wiley & Sons, Ltd.

Ba 2 Mg 2 Fe 12 O 22 is a Y-type hexagonal ferrite known for a relatively high temperature (∼200 K) of the magnetic transition to a spiral spin arrangement and an easy magnetization axis lying in a plane perpendicular to the c crystal axis. The multiferroicity exists in the absence of an external magnetic field H; a longitudinal-conical spin arrangement sets below 50 K; and the direction of the electric polarization P can be governed by relatively low magnetic fields ( 2 Mg 2 Fe 12 O 22 powders is scarce. We report on Ba 2 Mg 2 Fe 12 O 22 powders studied by X-ray and neutron powder diffraction, and magnetometry. The samples were prepared by two different techniques: sonochemical co-precipitation and sol-gel auto-combustion. The structures retained the rhombohedral crystal symmetry, but mixed occupancies of the 14 (Mg, Fe) cation sites was a new feature. The magnetizations at a magnetic field of 60 kOe at 300 K were 22.78 emu/g for the sample prepared by sol-gel auto-combustion, and 24.95 and 25.06 emu/g for the samples obtained by sonochemical co-precipitation and annealed at 1170 °C and 1200 °C, respectively.

In Hungary two geological sites of the Boda Claystone Formation (BCF) located in the W-Mecsek mountains (South Hungary) have been selected for the study of potential host rocks for high level radioactive waste, Gorica (G) Block and W-Mecsek Anticline (WMA) Block. The aim of the study was to obtain information on the uranium uptake characteristics of both sites. Our results revealed that in the sample, taken from WMA Block, where dolomites have ankerite rims and U-bearing rings, newly formed FeOOH precipitations were observed, which partly replaced the ankerite at near neutral pH (6.8). UO2 2+ ions were adsorbed easily due to the enhanced specific surface area and high adsorption capacity of FeOOH formed from the dissolution of ankerite. The oxidation of Fe2+ leads to the formation of FeOOH parallel to partial reduction of U6+ to U4+. 75 % of uranium was taken up by clay minerals and 25 % by FeOOH although the ankerite concentration is as low as 6 % in WMA Block of BCF. In G Block, the argillaceous matrix was found to be mainly responsible for the UO2 2+ uptake. The study demonstrated that the U retention capacity of different BCF locations was significantly influenced by the mineralogy of these sites.

Argillaceous rocks are considered in most European countries as suitable host rock formations for the deep geological disposal of high-level radioactive waste (HLW). The most important chemical characteristic in this respect is their generally strong radionuclide retention property due to the high sorption capacity. Consequently, the physico-chemical parameters of these processes have to be studied in great detail. Synchrotron radiation microscopic X-ray fluorescence (SR μ-XRF) has sufficient sensitivity to study these processes on the microscale without the necessity of the application of radioactive substances. The present study focuses on the interaction between the escaped ions and the host-rock surrounding the planned HLW repository. SR μ-XRF measurements were performed on thin sections subjected to sorption experiments using 5 μm spatial resolution. Inactive Cs(I), Ni(II), Nd(III) and natural U(VI) were selected for the experiments chemically representing key radionuclides. The thin sections were prepared on high-purity silicon wafers from geochemically characterized cores of Boda Claystone Formation, Hungary. Samples were subjected to 72-hour sorption experiments with one ion of interest added. The μ-XRF elemental maps taken usually on several thousand pixels indicate a correlation of Cs and Ni with Fe- and K-rich regions suggesting that these elements are predominantly taken up by clay-rich phases. U and Nd was found to be bound not only to the clayey matrix, but the cavity filling minerals also played important role in the uptake. Multivariate methods were found to be efficient tools for extracting information from the elemental distribution maps even when the clayey matrix and fracture infilling regions were examined in the same measured area. By using positive matrix factorization as a new approach the factors with higher sorption capacity could be identified and with additional mineralogical information the uptake capacity of the different mineral phases could be quantified. The results were compared with cluster analysis when the regions dominated by different mineral phases are segmented. The multivariate approach based on μ-XRF to identify the minerals was validated using microscopic X-ray diffraction.

New quaternary chalcogenide Ge x Sb 40− x S 50 Te 10 and Ge x Sb 40− x Se 50 Te 10 ( x =20 and 27 at%) glasses have been synthesized and studied by neutron and high-energy X-ray diffraction. Both the traditional Fourier transformation technique and the Reverse Monte Carlo (RMC) modeling of the experimental data have been applied to model the 3-dimensional atomic configurations. From the analysis of the partial atomic correlation functions and structure factors the first and second neighbor distances, coordination numbers and bond-angle distributions are calculated. The influence of S(Se) content on the atomic environment in the glassy structure is considered and discussed in a function of glass composition. In addition, the packing density, average atomic volume and compactness for each composition are determined.

Journal of physics / Conference Series 746, 012068 (2016). doi:10.1088/1742-6596/746/1/012068, Rare-earth molybdate glasses have been prepared by rapid quench technique, the network structure was investigated by neutron and high-energy X-ray diffraction. For data evaluation the reverse Monte Carlo simulation technique was applied to obtain a possible 3dimensional network configuration, which is consistent with the experimental data. From the modelling the partial atomic correlation functions g$_{iJ}$(r) and the coordination number distributions CN$_{iJ}$ have been revealed. Formation of MoO$_4$ (55%) and MoO$_6$ (25%) units was established for the binary 90MoO$_3$-10Nd$_2$O$_3$ glass. The B-O first neighbour distribution show a relatively broad first neighbour distance at 1.40A, the average coordination numbers show the presents of trigonal BO$_3$ and tetrahedral BO$_4$ groups. For 50MoO$_3$-25Nd$_2$O$_3$-25B$_2$O$_3$ sample mixed MoO$_4$-BO$_4$ and MoO$_4$-BO$_3$ linkages form pronounced intermediate-range order., Published by IOP Publ., Bristol

Neutron diffraction structure study has been performed on YAl3(BO3)4 (YAB), on doped Y0.88Er0.12Al3 (BO3)4 ,Y 0.5Er0.5Al3(BO3)4 ,Y 0.5Yb0.5Al3(BO3)4 and on co-doped Y0.84Er0.01Yb0.15Al3(BO3)4 compositions. It was established that the doped compounds are isostructural to YAB. The neutron diffraction pattern have been be fitted in space group R32 using the triple hexagonal Wyckoff notation. Both Er 3+ and Yb 3+ ions occupy the Y 3+ (3a) sites and not the Al 3+ (9d) sites, as it was suggested previously. The lattice parameters are decreasing with increasing amount of the dopant elements. Slight changes are revealed in the posi- tional parameters and interatomic distances with increasing concentration of the dopant ions. For the co-doped Y0.84Er0.01Yb0.15Al3(BO3)4 the changes are more significant than for the doped YAB compounds with only one type of dopant element, Er or Yb.

article i nfo Article history: Disordered solids; Optical properties; RMC simulation; Neutron diffraction; X-ray diffraction The atomic structures of amorphous As40Se(60−x)Tex (x=10 and 15) and As40Se60 glasses have been investigat- ed by neutron and high energy X-ray diffraction methods. The two datasets were modeled simultaneously by reverse Monte Carlo (RMC) simulation technique. The RMC simulations revealed a glassy network built-up from As(Se, Te)3 pyramids in which Te atoms substitute Se atoms. The As―Se correlation function shows a strong and sharp first peak at 2.4 A and two broad and much less intense peaks at 3.7 and 5.6 A, related to 1st, 2nd and 3rd neighbor distances of the As―Se bonds, respectively. They are an evidence for existence of short and medium ordering in the studied glasses. The similarity of ΘTe―As―Te and ΘSe―As―Se bond distributions suggests that Te atoms have a similar role in the structure formation as Se atoms. The FTIR spectra analysis revealed impurity bonds of Se―H, As―O, Se―O, and Te―O in the glasses which contributed to enhanced ab- sorption in visible spectral range. From the ellipsometric data analysis the optical constants and the energetic parameters of the studied glasses were established. The compositional variation of these parameters is explained in terms of chemical bonds formation and change in the density of charged defects.

A neutron diffraction study has been performed on newly synthesized v-B2O3 and 75B2O3–25Na2O glasses. The structure factor has been measured over a broad momentum transfer range, 0.4–30 A−1, which made fine r-space resolution available for real space analyses. The reverse Monte Carlo (RMC) method was successfully applied to calculate a possible 3-dimensional atomic configuration that is consistent with the measured structure factor. The partial atomic pair-correlation functions, nearest neighbor atomic distances, coordination number distributions, average coordination number values and three-particle bond angle distributions have been revealed. It was established that addition of 25 mol% Na2O to v-B2O3 transforms 41% of the 3-fold oxygen coordinated boron atoms into 4-fold coordinated ones. The first neighbor B–O distance is at 1.37 A in v-B2O3, while two well resolved distances are at 1.38 and 1.50 A in the 75B2O3–25Na2O glass. The three-particle 〈O–B–O〉 and 〈B–O–B〉 bond angle distributions show an extra peak at around 90° in the 75B2O3–25Na2O glass, which may be attributed to the BO4 units, in addition to the peak at 120° characteristic for BO3 trigonal units. The ring size distribution of the v-B2O3 network indicate that only 12% of boron atoms form boroxol group (B3O6), while the fraction of the larger 7–11 boron membered rings is 52%, and a tail of the distribution extends up to 20-membered rings.

New quaternary chalcogenide GexSb40� xS50Te10 (x = 10, 20 and 27 at.%) and GexSb40� xS55Te5 (x = 20 and 27 at.%) glasses have been synthesized and the compositions have been characterized applying prompt gamma-ray activation analyses, neutron diffraction, and material density measurements. Using the experimental data, the basic physical parameters, such as average atomic volume, packing density, compactness, average coordination number, number of constrains, average heat of atomization and cohesive energy, of the synthesized glasses are evaluated and the results are discussed in a function of glass composition.

New quaternary telluride glassy materials with composition of Ge x Sb 40− x S 50 Te 10 and Ge x Sb 40− x S 55 Te 5 ( x = 10, 20, and 27) have been synthesized and their optical properties have been studied by means of spectroscopic ellipsometry in the range of 400–820 nm. The optical constants, i.e. the refractive index, extinction coefficient, absorption coefficient, and the optical band gap energy are determined and their compositional dependence is considered. These parameters are characteristics for amorphous structure of the synthesized glasses, revealed from the neutron diffraction measurements.

The effect of uranium oxide on the structure of sodium borosilicate host glasses has been studied by neutron diffraction. The samples were prepared by quenching the melted mixtures of composition 70 wt% [(65 − x)SiO2 · xB2O3 · 25Na2O · 5BaO · 5ZrO2] + 30 wt% UO3 with x = 5, 10 and 15 mol%. It was found, that the U-loaded glasses posses good glass and hydrolytic stability. An enhanced probability for inter-mediate atomic correlations at around 4.8 A has been established. The RMC simulation of the neutron diffraction data is consistent with a model where the uranium ions are incorporated into interstitial voids in the essentially unmodified network structure of the starting host glass. The U–O atomic pair correlation functions show a sharp peak at around 1.7 A, and several farther distinct peaks are at 2.8, 3.6 and 4.1 A. The uranium ions are coordinated by six oxygen atoms in the 1.6–3.4 A interval.

Neutron diffraction structure study has been performed on multi-component sodium borosilicate based waste glasses with the composition of (65 � x)SiO2. AE xB2O3 AE 25Na2O AE 5BaO AE 5ZrO2, x = 5–15 mol%. The maximum momentum transfer of the experimental structure factor was 30 A ˚ � 1 , which made available to determine the distribution function with high r-space resolution. Reverse Monte Carlo modelling was applied to calculate several partial atomic pair correlation functions, nearest neighbor distances and coordination numbers have been revealed. The characteristic features of Si–O and Si–Si distributions are similar for all glassy samples, suggesting that the Si–O network consisting of tetrahedral SiO4 units is highly stable even in the multi-component glasses. The B–O correlations proved

The structure of molybdate glasses have been investigated by neutron and high-energy X-ray diffraction coupled with Reverse Monte Carlo (RMC) simulation technique. From the modelling the partial atomic correlation functions g ij(r), the coordination number distributions CN ij and bond angle distributions have been revealed. For binary 90MoO3-10Nd2O3 glass composition the fraction of MoO4/MoO6 was 0.55/0.25. Three type of ternary system have been studied, where the most important structural units was authenticated. For MoO3-Nd2O3-B2O3 sample mixed MoO4-BO4 and MoO4-BO3 linkages form pronounced intermediate-range order. In case of MoO3-ZnO-B2O3 series the BO3 and BO4 units are linked to MoO4 and/or ZnO4, forming mixed MoO4-BO4(BO3), MoO4-ZnO4 and ZnO4-BO4(BO3) bond-linkages.

Neutron- and high-energy synchrotron x-ray diffraction experiments have been performed on the (75− x )SiO 2 – x B 2 O 3 –25Na 2 O x = 5, 10, 15 and 20 mol% glasses. The structure factor has been measured over a broad momentum transfer range, between 0.4 and 22 A −1 . For data analyses and modelling the Fourier transformation and the reverse Monte Carlo simulation techniques have been applied. The partial atomic pair correlation functions, the nearest neighbour distances, coordination number distributions and average coordination number values and three-particle bond angle distributions have been revealed. The Si–O network proved to be highly stable consisting of SiO 4 tetrahedral units with characteristic distances at r Si–O = 1.60 A and r Si–Si = 3.0(5) A. The behaviour of network forming boron atoms proved to be more complex. The first neighbour B–O distances show two distinct values at 1.30 A and a characteristic peak at 1.5(5) A and, both trigonal BO 3 and tetrahedral BO 4 units are present. The relative abundance of BO 4 and BO 3 units depend on the boron content, and with increasing boron content the number of BO 4 is decreasing, while BO 3 is increasing.

Neutron and high-energy x-ray diffraction measurements have been performed on multi-component 55SiO(2)·10B(2)O(3)·25Na(2)O·5BaO·ZrO(2) borosilicate host glass loaded with 30 wt% UO(3). Both the traditional Fourier transformation technique and the reverse Monte Carlo simulation of the experimental data have been applied to get structural information. It was established that the basic network structure consists of tetrahedral SiO(4) units and of mixed tetrahedral BO(4) and trigonal BO(3) units, similar to the corresponding host glass. Slight changes have been observed in the oxygen surroundings of the Na and Zr modifier cations; both the Na-O and Zr-O distances decrease and a more compact short-range structure has been obtained compared to the host glass. For the U-O correlations two distinct peaks were resolved at 1.84 and 2.24 Å, and for higher distances intermediate-range correlations were observed. Significant correlations have been revealed between U and the network former Si and B atoms. Uranium ions take part in the network forming, which may be the reason for the observed good glassy stability and hydrolytic properties.

The network structure of boromolybdate MoO3-Nd2O3-B2O3 glasses has been investigated by neutron diffraction and reverse Monte Carlo (RMC) simulation technique. The partial atomic correlation functions, first neighbour atom distances and the coordination numbers have been revealed. Formation of MoO4 (55%) and MoO6 (45%) units was established for the binary 90MoO3-10Nd2O3 glass. The ternary glasses consist from MoO4, BO3 and BO4 units. The relative number of BO3 is increasing with increasing boron content. Characteristic second neighbour distributions indicate the existence of a pronounced intermediate-range ordering through MoO4-BO4 and MoO4-BO3 linkages.