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 CNij and bond angle distributions have been revealed. For binary 90MoO(3)-10Nd(2)O(3) 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.

The crystal structure of oxygen-deficient BaCe(0.85)Y(0.15)O3-delta (BCY15) materials prepared by auto-combustion with following calcination at high temperature was determined from neutron and X-ray powder diffraction. The materials were used recently as cathode, anode and central membrane in a novel design of SOFC: dual membrane fuel cell (dmFC). The dmFC design exploits the good mixed (protonic and oxide ion) conductivity in BaCe0.85Y0.15O2.825 at working temperatures of 600-700 degrees C. It allows the introduction of a separate compartment (central membrane) for water formation and evacuation. The central membrane has mixed ionic conductivity ensured by a composite material and porous microstructure. Profile refinements within the orthorhombic space group Pnma reproduced the neutron diffraction profiles of all the materials (dense, porous, powder) based on BCY15 conductivity presenting similar model crystal structures to protonic conductor BaCe0.9Y0.10O2.95 and the parent undoped BaCeO3 perovskite.

The structural details of powder, dense and porous samples of BaCe0.85Y0.15O3-delta (BCY15) used recently in an innovative monolithic design of SOFC were studied from multiple Rietveld analysis of neutron and x-ray diffraction patterns. The 3-layered monolithic assembly built from BCY15 material works as oxide ion conductor in the oxygen space, as proton conductor in the hydrogen area and as mixed conductor in the central membrane. We find that in all the samples of studied BCY15 based materials there are no indications of difference in crystallographic symmetry and the structure refinements did produce best agreement factors in orthorhombic Pnma space group.

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 giJ(r) and the coordination number distributions CNij have been revealed. Formation of MoO4 (55%) and MoO6 (25%) units was established for the binary 90MoO3-10Nd2O3 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 BO3 and tetrahedral BO4 groups. For 50MoO3-25Nd2O3-25B2O3 sample mixed MoO4-BO4 and MoO4-BO3 linkages form pronounced intermediate-range order.

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 90MoO(3)-10Nd(2)O(3) 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.

New quaternary chalcogenide GexSb40−xS50Te10 and GexSb40−xSe50Te10 (x=20 and 27at%) 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.

The structure of multi-component borosilicate SiO2–B2O3–Na2O–BaO–ZrO2 glass loaded with 30wt.% UO3 was investigated by neutron diffraction and high-energy X-ray diffraction. Reverse Monte Carlo modelling was applied to obtain a possible 3-dimensional atomic configuration consistent with the experimental data. It was established that the glassy network consists of tetrahedral SiO4 and of mixed tetrahedral BO4 and trigonal BO3 units. With increasing boron content the relative number of BO3/BO4 increases and the first neighbour rBO distance decreases. For the UO correlations two distinct first neighbour distances were determined at 1.8Å with 1.9 oxygen atoms and at 2.2Å with 3.7 oxygen atoms. Significant second neighbour correlations have been established between uranium and the network former (Si, B), the modifier (Na) and the stabilizer (Zr) atoms. From these observations we may conclude that uranium ions take part in the network forming. This may be the reason of the observed good glassy stability and hydrolytic properties.

Neutron diffraction structure study has been performed on YAl3(BO3)4 (YAB), on doped Y0.88Er0.12Al3(BO3)4, Y0.5Er0.5Al3(BO3)4, Y0.5Yb0.5Al3(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 Er3+ and Yb3+ ions occupy the Y3+ (3a) sites and not the Al3+ (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 positional 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.

s. KovACHEv-, D. KoVACHEVAU, s. ALEKSovsKAo, E. svAB", K. KREZHov Institutefor Nuclear Research and Nuclear Energy, Bulgarian Academy ofSciences, T2 Tzarigradsko Chaussee Blvd., 1781 Sofia, Bulgaria. o Institute ofGeneral and Inorganic Chemistry, Bulgarian Academy ofScience, "Acad. Georgi Bonchev" str. bld. I 1, I I 1 3 Sofia, Bulgaria. b Institute of Chemisíry, Faculty of Natural Sciences and Mathematics, I}niversity,,Sts. Cyril and Methodius,,, 1000 Skopje, Republic of Macedonia. " Research Institutefor Solid State Physics and Optics, H-1525 Budapest, POB 19, Hungary.

The atomic structures of amorphous As40Se(60−x)Tex (x = 10 and 15) and As40Se60 glasses have been investigated 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 Å and two broad and much less intense peaks at 3.7 and 5.6 Å, 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 absorption 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.

YCr1-xFexO3 materials with x = 0; 0.125; 0.25; 0.33; 0.5; 0.67; 0.75; 0.875 and 1 have been prepared by solution combustion method followed by thermal treatment at 800 degrees C in air. X-ray powder diffraction spectra of samples confirmed the formation of solid solutions within the whole concentration interval. All spectra were successfully indexed in orthorhombic Pnma space group. Neutron diffraction measurements at room temperature have confirmed that some of the samples studied are antiferromagnetically ordered. This is consistent with the asymptotic Curie temperatures determined from the dependence of the reverse magnetic susceptibility on temperature The effective magnetic moments were determined from the Rietveld refinement of the neutron powder diffraction data.

A neutron diffraction structure study has been performed on newly synthesized Ge20As20Se50Te10 and Ge27As13Se50Te10 chalcogenide glasses. Oscillations in the structure factor, S(Q) have been measured with good sign-to-noise up to 35 Å−1. The reverse Monte Carlo simulation was used to model the 3-dimensional atomic configuration. The partial atomic correlation functions and structure factors have been revealed. Several first and second neighbour distances, and coordination numbers have been calculated. We have established that several first neighbour atomic distances are overlapping at two characteristic distances, namely the Ge-Ge, Ge-Se and As-Se are centred at 2.42 Å, while the Ge-Te, As-Te and Se-Te are centred at 2.60 Å.

Multi-component alkali borosilicate and phosphate based glasses are known as most promising host materials for immobilizing of high-level radioactive wastes, like U-, Pu-, Th-oxides [1-3]. We have undertaken a structural study on multi-component borosilicate glasses and the corresponding compositions loaded with uranium [4-7]. In this work we have extended our previous neutron diffraction (ND) study with high-energy X-ray diffraction (XD), with the aim to obtain information on the uranium surrounding. In this report we present results on 55SiO2·10B2O3·25Na2O·5BaO·5ZrO2 host glass and the same composition loaded with 30wt%UO3 (referred as B10 and UB10) (for more details see [8]).

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.

Neutron and high-energy X-ray diffraction measurements have been performed on As40Se60 and As40Se50Te10 glasses. Both the traditional Fourier transformation technique and the reverse Monte Carlo (RMC) simulation 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 neighbour distances, coordination numbers and bond-angle distributions were calculated. It is established that substitution of Se by Te does not change the basic glassy network structure. For the As-Se bonding is revealed that the first neighbour distance is at 2.42 angstrom, the average coordination numbers are CNAsSe=2.6 +/- 0.1 and CNSeAs=1.8 +/- 0.1 atoms and the three-atom-bond angle for < Se-As-Se >, < As-Se-As > configurations is 95 degrees, the same value within limit of error, as obtained from RMC calculations.

New quaternary telluride glassy materials with composition of GexSb40−xS50Te10 and GexSb40−xS55Te5 (x=10, 20, and 27) have been synthesized and their optical properties have been studied by means of spectroscopic ellipsometry in the range of 400–820nm. 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.

Samples from the mixed oxide system YCr1-xFexO3 (0 <= x <= 1) were prepared by self-propagation combustion techniques and studied by neutron and X-ray diffraction at 290 K and by magnetic measurements in the range 2-800 K. The average observed metal-oxygen distances based on refinements in the space group Pnma are in agreement with the expected distances from the valence bond approach. The non-collinear spin arrangement (mode Gamma 4) of YFeO3 and YCrO3 is preserved for the rest (x >= 0.33) of the compounds magnetic at 290 K. The findings indicate that YCrO3 and YFeO3 form a solid solution with strongly frustrated magnetic interactions.