Search results for "Neutron diffraction"
showing 10 items of 102 documents
A new method for data evaluation of small angle neutron scattering experiments and its application to amorphous polycarbonate
1981
The conformation of single chains in bulk polymer materials can be evaluated from coherent neutron scattering on mixtures of normal and deuterated polymers. It is shown that the single-chain structure factor can be also obtained from measurements of highly concentrated mixtures and the procedure of evaluation is described. The application to amorphous polycarbonate demonstrates the advantages of the method.
Crystal structure determination of 1-pentanol from low-temperature powder diffraction data by Patterson search methods
2005
5 pages.-- PACS: 61.66.Hq; 61.50.Lt
Magnetic order in UCu4+xAl8−x
1992
Abstract A neutron diffraction study has been performed on UCu4+xAl8−x. The compound was chosen as an example of a uranium-based system, which goes from a magnetically ordered state to a pure heavy-fermion state. In the range x = 0.25–1, UCu4+xAl8−x orders in a simple collinear antiferromagnetic structure. With increasing concentration of Cu, the ordering temperature decreases and moment compensation develops due to the increasing hybridization of the 5f electrons.
Heptane adsorption in silicalite-1 : molecular dynamics simulation.
2009
Molecular dynamics (MD) simulations have been used to study the adsorption process of n-heptane molecules in silicalite-1 at 300 K. MD simulated results were compared to experimental neutron diffraction (ND) and experimental self-diffusion coefficients. The analysis of MD data indicated a packing of the adsorbed molecules around 4 mol./u.c., which is not the consequence of an enthalpic effect but of an entropic effect. The role of the n-heptane chain flexibility (cis–trans conformation) in relation with the silicalite-1 channel type (straight versus sinusoidal) was outlined and enabled to understand the mobility change arising at 4 mol./u.c., according to previous experimental results. The …
Magnetic Ordering and Spin Dynamics of Ba1-xEuxSi Phases
2011
We have investigated the magnetic ordering and spin dynamics of the solid solution series Ba1–xEuxSi with 0 < x ≤ 1 applying X-ray diffraction, electric conductivity measurements, Mossbauer spectroscopy, muon spin depolarization, and neutron diffraction. Our results suggest a spin glass-like behavior of Ba1–xEuxSi for concentrations close to x = 0.3 exist. Different spin ordering phenomena are found, which are dependent on the relative europium concentrations.
Spin Density Maps in the Triplet Ground State of [Cu2(t-Bupy)4(N3)2](ClO4)2 (t-Bupy = p-tert-butylpyridine): A Polarized Neutron Diffraction Study
1998
This paper is devoted to the determination of the spin distribution in the spin triplet ground state of [Cu-2(t-Bupy)(4)(N-3)(2)](ClO4)(2), With t-Bupy = p-tert-butylpyridine. The crystal structure, previously solved at room temperature from X-ray diffraction, has been redetermined at 18 K from unpolarized neutron diffraction. The structure consists of binuclear cations in which Cu2+ ions are doubly bridged by azido groups in the 1,1-fashion, and noncoordinated perchlorate anions. The experimental spin distribution has been determined from polarized neutron diffraction (PND) at 1.6 K under 50 kOe. The spin populations have been found to be strongly positive on the Cu2+ ions, weakly positive…
Thermodynamic and Neutron-Diffraction Studies of H2 and D2 Multilayers Physisorbed on Graphite
1991
The evolution of physisorbed films from two-dimensional (2D) to bulk behavior is a topic of high current interest.1 In this context the behavior of the quantum systems H2, HD and D2 is of particular relevance because of the following reasons: 1. Due to the strong influence of the quantum zero-point energy the hydrogen isotopes are highly compressible. This leads to strongly compressed monolayers2,3 before further layer condensation occurs. This property makes these systems significant for the exploration of conditions of multilayer growth. It is generally believed,1,4–6 that the incompatibility between the adsorbate and bulk lattice structures gives rise to lateral strains between the overl…
Ab initiothermodynamics ofBacSr(1−c)TiO3solid solutions
2005
Based on ab initio calculations for a number of the ${\mathrm{Ba}}_{\mathrm{c}}{\mathrm{Sr}}_{(1\ensuremath{-}\mathrm{c})}\mathrm{Ti}{\mathrm{O}}_{3}$ (BST) superlattices, we developed a thermodynamic approach to these solid solutions. In particular, we calculate the BST phase diagram and show that at relatively low temperatures (below $400\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for $c=0.5$ and $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for $c=0.1$) the spinodal decomposition of the solid solution occurs. As a result, we predict for small Ba concentrations formation of $\mathrm{Ba}\mathrm{Ti}{\mathrm{O}}_{3}$ nanoregions in a predominantly $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ matrix and …
Measuring Multiple Residual-Stress Components using the Contour Method and Multiple Cuts
2009
The conventional contour method determines one component of residual stress over the cross section of a part. The part is cut into two, the contour (topographic shape) of the exposed surface is measured, and Bueckner’s superposition principle is analytically applied to calculate stresses. In this paper, the contour method is extended to the measurement of multiple residual-stress components by making multiple cuts with subsequent applications of superposition. The theory and limitations are described. The theory is experimentally tested on a 316L stainless steel disk with residual stresses induced by plastically indenting the central portion of the disk. The multiple-cut contour method resu…
Adsorption of m-Xylene on Prehydrated Zeolite BaX: Correlation between Temperature-Programmed Desorption and Low-Temperature Neutron Powder Diffract…
1999
Adsorption of m-xylene on partially hydrated zeolite BaX is studied by thermogravimetry, mass spectrometry, temperature-programmed desorption and neutron diffraction for different m-xylene loadings of the zeolite. Macroscopic and microscopic measurements, for both molecules, were correlated and relationships were found between the crystallographic positions of the adsorbed molecules on the zeolite and macroscopic properties such as the number and the area of the peaks in the desorption spectra for m-xylene or water. The influence of water molecules on the adsorption phenomenon of m-xylene on BaX zeolite was characterized. In particular, it was shown that the increase of the filling of the p…