Short-range order in amorphous Ni83Lalv was examined by neutron and X-ray diffraction. Computer m... more Short-range order in amorphous Ni83Lalv was examined by neutron and X-ray diffraction. Computer modelling was based on a new method using the molecular dynamics technique and the Born-Green-Bogoljubov equation. All three partial pair correlation functions and characteristic structure parameters are derived.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2005
The problems of corrosion and deposit are crucial issues in the pipelines of the chemical, nuclea... more The problems of corrosion and deposit are crucial issues in the pipelines of the chemical, nuclear and petrochemical industries. Radiography (neutron, gamma, X-ray) has long been used as a technique for pipe inspection and corrosion monitoring. The 10 MW Budapest research reactor site is a source of various energy neutron (thermal and epithermal) and gamma radiation. The detector system was a Peltier-cooled LLL CCD camera controlled by a PC with Image ProLite software and imaging plate equipment with a BAS 2500 scanner that used AIDA software. The objects inspected were corroded tubes and various kinds of test specimens with a large wall thickness (25 mm) inside and outside steps. In the evaluation part we used tomographic algorithms. A software simulation study was made as well. Fan-beam projections were computed of the given software phantoms and a new discrete tomography method was used to reconstruct the unknown objects from these projections.
Neutron diffraction structure study has been performed on multi-component sodium borosilicate bas... more Neutron diffraction structure study has been performed on multi-component sodium borosilicate based waste glasses with the composition of (65 À x)SiO 2. AE xB 2 O 3 AE 25Na 2 O AE 5BaO AE 5ZrO 2 , x = 5-15 mol%. The maximum momentum transfer of the experimental structure factor was 30 Å À1 , 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 SiO 4 units is highly stable even in the multi-component glasses. The B-O correlations proved to be fairly complex, two distinct first neighbor distances are present at 1.40 Å and 1.60 Å , the latter equals the Si-O distance. Coordination number distribution analyzes has revealed 3 and four-coordinated boron atoms. The O-O distribution suggests a network configuration consisting of boron rich and silicon rich regions. Our findings are consistent with a structure model where the boron rich network contains mostly trigonal BO 3 units, and the silicon rich network is formed by a mixed continuous network of [4] Si-O-Si [4] with several different [4] B-O-Si [4] and [3] B-O-Si [4] linkages.
A neutron diffraction structure study has been performed on multi-component borosilicate glasses ... more A neutron diffraction structure study has been performed on multi-component borosilicate glasses with compositions (65 À x)SiO 2 Á xB 2 O 3 Á 25Na 2 O Á 5BaO Á 5ZrO 2 , x = 5-15 mol%. The structure factor has been measured up to a rather high momentum transfer value of 30 Å À1 , which made high r-space resolution available for real space analyses. Reverse Monte Carlo simulation was applied to calculate the partial atomic pair correlation functions, nearest neighbor atomic distances and coordination number distributions. The Si-O network consists of tetrahedral SiO 4 units with characteristic first neighbor distances at r Si-O = 1.60 Å and r Si-Si = 3.0 Å. The boron environment contains two well-resolved B-O distances at 1.40 and 1.60 Å and both 3-and 4-fold coordinated B atoms are present. A chemically mixed network structure is proposed including [4] B-O-[4] Si and [3] B-O-[4] Si chain segments. The O-O and Na-O distributions suggest partial segregation of silicon and boron rich regions. The highly effective ability of Zr to stabilize glassy and hydrolytic properties of sodium-borosilicate materials is interpreted by the network-forming role of Zr ions.
The atomic structures of amorphous As 40 Se (60−x) Te x (x= 10 and 15) and As 40 Se 60 glasses ha... more The atomic structures of amorphous As 40 Se (60−x) Te x (x= 10 and 15) and As 40 Se 60 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 Θ TeAs -Te and Θ SeAs -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.
Applied Physics A: Materials Science & Processing, 2002
Powder neutron and X-ray diffraction patterns of nanocrystalline needle-shaped maghemite (γ-Fe 2 ... more Powder neutron and X-ray diffraction patterns of nanocrystalline needle-shaped maghemite (γ-Fe 2 O 3) particles with average size 240 nm × 30 nm show the presence of superstructure peaks indicating a long-range ordering of the cation vacancies. The crystallographic parameters, the characteristics of the tetragonal distortion, and the vacancy distribution were determined in space group P4 1 2 1 2 by multiprofile Rietveld refinement.
Acta Crystallographica Section A Foundations of Crystallography, 2002
Nanoparticles will become an important factor in the scale-down attempts of future technologies. ... more Nanoparticles will become an important factor in the scale-down attempts of future technologies. However, there is a need for a toolbox for applying such materials in a flexible and creative way. Anisotropic nanomaterials may play here a key role because they exhibit morphological prefunctionalizations which allow for new physical effects, elegant orientation techniques, and morphological design of functional nanoparticles. We are concentrating on oxidic nanotube and nanofiber materials by developing reliable synthesis procedures, characterization techniques and application pathways. There is a growing need for synthetic guidelines that can be applied on the preparation and tailoring of nanomaterials. Systematic studies reveal that some elementary synthetic parameters like selection of inorganic ionic additives and solvent control of temperature as well as reaction times allow for the design of novel transition metal oxide nanorods via flexible high-quality solvothermal syntheses [1, 2]. Furthermore, all these preparative advantages can be customized again by variation of additive concentration, reaction time and temperature of a standard procedure. Thus, a large selection of synthetic tools has been established: a precise approach to oxidic nanorods with desired compositions and aspect ratios. [1] G. R.
The structure of molybdate glasses have been investigated by neutron and high-energy X-ray diffra... more 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.
Rare-earth molybdate glasses have been prepared by rapid quench technique, the network structure ... more 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 1.40Å, 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.
The crystal structure of oxygen-deficient BaCe0.85Y0.15O3−δ (BCY15) materials prepared by auto-co... more The crystal structure of oxygen-deficient BaCe0.85Y0.15O3−δ (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 BaCe 0.85Y0.15O2.825 at working temperatures of 600-700 o 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 BaCe 0.9Y0.10O2.95 and the parent undoped BaCeO3 perovskite.
Neutron Diffraction Investigation of Pb[sub 0.5]La[sub 0.5]FeO[sub 3]
Pb0.5La0.5FeO3 has been synthesized by a single‐step solution combustion method using sucrose as ... more Pb0.5La0.5FeO3 has been synthesized by a single‐step solution combustion method using sucrose as a fuel. The combustion‐synthesized material was characterized by differential thermal analysis (DTA), magnetic measurements, powder X‐ray diffraction and neutron diffraction. The crystal structure examined by the diffraction methods indicates that the material is single‐phase, and crystallizes in an orthorhombic (space group, Pnma) structure. Similarly to parent LaFeO3, the lead doped compound showed canted antiferromagnetic behavior associated with an increase in magnetic moment. The changes in magnetic properties of the material are correlated to the changes in structural features resulting from the Rietveld structural refinement of the diffraction patterns.
The structural details of powder, dense and porous samples of BaCe 0.85 Y 0.15 O 3−δ (BCY15) used... more The structural details of powder, dense and porous samples of BaCe 0.85 Y 0.15 O 3−δ (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.
Thermal stability and crystallization of transition metal-boron metallic glasses
The crystallization of (Fe sub(1-x)TM sub x sub (75+y) B sub (25-y) - TM = Co and Ni - glasses ar... more The crystallization of (Fe sub(1-x)TM sub x sub (75+y) B sub (25-y) - TM = Co and Ni - glasses are investigated in the 0 x 1, 0 y 10 composites range by calorimetry, X-ray diffraction and Mossbauer spectroscopy. The crystalline phases are identified and their relation to possible changes in the chemical short range order of these amorphous alloys
Small-angle neutron scattering study of FeB and FeNiB metallic glasses
Neutron-diffraction measurements have been used to 'determine the temperature and composition dep... more Neutron-diffraction measurements have been used to 'determine the temperature and composition dependences of the ordered single crystals of Pt-Fe alloys containing 32, 30.5 and 28 at% of iron. A qualitative model for the complex antiferromagnetic ordering in the system based on the experimental data and band structure calculations has been proposed.
Samples from the mixed oxide system YCn-"Fe,Og (0<x<1) were prepared by self-propagation combusti... more Samples from the mixed oxide system YCn-"Fe,Og (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 l-4) of YFeOg and YCrOs is preserved Íor the rest (x >0.33) of the compounds magnetic at 290 K. The findings indicate that YCrog and YFeos form a solid solution with strongly frustrated magnetic interactions.
Structure and Properties Investigation of Mixed Oxides YCr[sub 1−x]Fe[sub x]O[sub 3] (0≤x≤1)
ABSTRACT YCr{sub 1-x}FeO materials with x = 0; 0.125; 0.25; 0.33; 0.5; 0.67; 0.75; 0.875 and 1 ha... more ABSTRACT YCr{sub 1-x}FeO 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 deg. 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.
View the article online for updates and enhancements. Related content Basic network structure of ... more View the article online for updates and enhancements. Related content Basic network structure of SiO2-B2O3-Na2O glasses from diffraction and Reverse Monte Carlo simulation M Fábián and Cs Araczki-Uranium surroundings in borosilicate glass from neutron and x-ray diffraction and RMCmodelling M Fábián, Th Proffen, U Ruett et al.-Structure study of chalcogenide glasses from high Q-range neutron diffraction experiment and RMC modelling M Fábián, E Sváb, S Vogel et al.-Recent citations Structure of xMoO 3-(100-x)TeO 2 glasses by neutron diffraction and Reverse Monte Carlo modeling Atul Khanna et al
Uploads
Papers by E. Svab