It is well known that in standard diffaction experiments only the amplitudes of structural Fourier components are recovered but phase information is lost. This problem is known as the ’phase problem’ in crystallography. In this contribution, we point out how the phase problem of diffraction can be solved in some particular cases by employing multi-wave interference. In the experimental situation described here, we were able to determine the form of the refractive-index profile of a 1-D nanocomposite holographic grating by using a multi-wave coupling analysis of the measured angular dependence of the diffraction efficiencies for a number of diffraction orders.

Co–Re alloys are being developed for ultra-high-temperature applications to supplement Ni-based superalloys in future gas turbines. The main goal of the alloy development is to increase the maximum service temperature of the alloy beyond 1473 K, i.e. at least 100 K more than the present single-crystal Ni-based superalloy turbine blades. Co–Re alloys are strengthened by carbide phases, particularly the monocarbide of Ta. The binary TaC phase is stable at very high temperatures, much greater than the melting temperature of superalloys and Co–Re alloys. However, its stability within the Co–Re–Cr system has never been studied systematically. In this study an alloy with the composition Co–17Re–23Cr–1.2Ta–2.6C was investigated using complementary methods of small-angle neutron scattering (SANS), scanning electron microscopy, X-ray diffraction and neutron diffraction. Samples heat treated externally and samples heated in situ during diffraction experiments exhibited stable TaC precipitates at temperatures up to 1573 K. The size and volume fraction of fine TaC precipitates (up to 100 nm) were characterized at high temperatures with in situ SANS measurements. Moreover, SANS was used to monitor precipitate formation during cooling from high temperatures. When the alloy is heated the matrix undergoes an allotropic phase transformation from the ∊ phase (hexagonal close-packed) to the γ phase (face-centred cubic), and the influence on the strengthening TaC precipitates was also studied with in situ SANS. The results show that the TaC phase is stable and at these high temperatures the precipitates coarsen but still remain. This makes the TaC precipitates attractive and the Co–Re alloys a promising candidate for high-temperature application.

The interaction between biosurfactant Surfactin and cationic Gemini surfactant ethanediyl-1,3-bis(dodecyldimethylammonium bromide) (abbreviated as 12-3-12) was investigated using turbidity, surface tension, dynamic light scattering (DLS) and small angle neutron scattering (SANS). Analysis of critical micelle concentration (CMC) values in Surfactin/12-3-12 mixture indicates that there is synergism in formation of mixed Surfactin/12-3-12 micelles. Although Surfactin and 12-3-12 are oppositely charged in phosphate buffer solution (PBS, pH7.4), there are no precipitates observed at the concentrations below the CMC of Surfactin/12-3-12 system. However, at the concentration above CMC value, the Surfactin/12-3-12 mixture is severely turbid with high 12-3-12 content. DLS and SANS measurements follow the size and shape changes of mixed Surfactin/12-3-12 aggregates from small spherical micelles via elongated aggregates to large bulk complexes with increasing fraction of Gemini surfactant.

Mg-Dy alloys are attractive for biomaterial applications. Their mechanical property profile is close to that of cortical hone, they are non-toxic, osseoconductive and degradable. Their macroscopic characteristics depend on their microstructure, which can be tailored through the alloy composition and the solidification parameters. In situ synchrotron radiation diffraction is a tool to unequivocally follow the phase formation and grain growth during cooling, thus determining the solidification sequence. In the present study Mg alloys containing Dy and Zr were investigated to characterize the solidification phenomenon during cooling from 660 degrees C to 200 degrees C. Samples, contained in steel crucibles, were melted in a modified induction furnace for in situ synchrotron radiation measurements at the HZG beamline P07B (HEMS) at PETRA III, DESY, with the temperature controlled by type K thermocouples during the measurements. The results give an experimental validation of the thermodynamic calculations and input for refining the existing thermodynamic models. This contributes to a better understanding of the microstructure evolution thus to control desirable macroscopic characteristics.

Co-Re alloy development is prompted by the search for new materials for future gas turbines which can be used at temperatures considerably higher than the current day single crystal Ni-based superalloys. The Co-Re-based alloys have been designed to have very high melting range, and they are meant for application at +373 K (+100 °C) above Ni-superalloys. They are significantly different from the conventional Co-based alloys that are used in static components of today’s gas turbines, and the Co-Re alloys have never been used for structural applications before. The Co-Re-Cr system has complex microstructure with many different phases present. Phase transformations and stabilities of fine strengthening precipitates at high temperatures remain mostly unexplored in the Co-Re alloys, and to develop basic understanding, model ternary and quaternary compositions were studied within the alloy development program. In situ neutron and synchrotron measurements at high temperatures were extensively used for this purpose, and some recent results from the in situ measurements are presented. In particular, the effect of boron doping in Co-Re alloys and the stabilities of the fine TaC precipitates at high temperatures were investigated. A fine dispersion of TaC precipitates strengthens some Co-Re alloys, and their stabilities at the application temperatures are critical. In the beginning, the alloy development strategy is very briefly discussed.

We report grain-size-dependent results on nanocrystalline bulk Gd obtained by magnetic small-angle neutron scattering (SANS) and magnetometry. This approach allows one to study systematically how the magnetic microstructure of this rare-earth metal is affected by defects in the atomic microstructure, which are largely present in nanocrystalline materials, predominantly in the form of grain boundaries. The neutron scattering data reveal two types of angular anisotropies in the magnetic-field-dependent scattering cross section that are typically not seen in the coarse-grained polycrystal. In particular, a cloverleaf-shaped anisotropy and an elongation of the scattering pattern in the direction of the applied magnetic field have been detected. While the first result, which is an exceptional finding even in the nanocrystalline state, can be attributed to pronounced spin disorder in the vicinity of the Gd grain boundaries, the second anisotropy is related to spin misalignment due to the random magnetocrystalline anisotropy within the individual crystallites. Furthermore, we have calculated the correlation function of the spin misalignment from the radially averaged data, which gives access to the characteristic length scales on which the magnetization is perturbed by crystal defects. The results of this real-space analysis independently support the findings from magnetometry and field-dependent SANS. Wide-angle x-ray diffraction data indicate that stacking faults may limit the range of spin-misalignment fluctuations due to random anisotropy in this material.

MnSi crystals with chemically induced negative pressure (doped by less than 1% Ge) have been synthesized by the Czochralski method. X-ray powder diffraction has revealed that the samples are crystallized in the B20 structure, inherent to pure MnSi, without any impurity phases. The lattice constant a is slightly larger than that of undoped MnSi. The samples have a spiral spin structure with the wave vector vertical bar k vertical bar = 0.385 nm(-1) at low temperatures. The ordering temperature is enhanced up to T-C = 39 K. The critical field H-C2 shows an increase of about 25% for the doped samples. Close to the critical temperature the A phase occurs. The temperature range of the A phase in the (H-T) phase diagram for the doped compound ranges from TA = 27.5 K, characteristic for pure MnSi, to T-C = 39 K in the zero-field cooled (ZFC) regime of magnetization. The magnetic features of the (H-T) phase diagram of the compounds MnSi are reminiscent of those observed for the MnSi thin films on the Si substrate.

We discuss the applicability of holographically patterned polymers, polymer dispersed liquid crystals, and nano-particle-polymer composites as optical elements for cold neutrons. Requirements concerning the spacing, thickness or strength of the grating for certain types of neutron optical elements, e.g., 2-port or 3-port beamsplitters, are discussed in the framework of a rigorous coupled-wave analysis. Finally, a roadmap to neutron mirrors, e.g., for interferometers, is drawn.

The critical spin fluctuations in Mn1-yFeySi compounds have been studied by means of ac-susceptibility measurements, polarized neutron small angle scattering, and spin echo spectroscopy. It is shown that these compounds undergo the transition from the paramagnetic to helimagnetic phase through continuous yet well distinguishable crossovers: (i) from paramagnetic to partially chiral and (ii) from partially chiral to highly chiral fluctuating state. The temperature crossovers are associated with the enhancing influence of the Dzyaloshinskii-Moria interaction close to T-c.

C388 DSC/TGA thermal analysis. FT-IR spectra of the compounds indicates the nature of the metal-ligand coordination environment. Presence of ν(O-H) shifted to lower energy indicated H-bonded carboxylic acid, while νas(COO) and νs(COO) splitting show both monodentate and bidentate carboxylate coordination [2]. Monodentate SO4 (C3v) and bidentate bridging SO4 (C2v) modes can also be inferred from infrared spectral analysis.

Titania nanotube arrays were synthesized via anodic oxidation of titanium foils in glycerol electrolyte containing NH4F at anodization voltage ranging from 10V to 30V. The structural parameters of self-organized periodic arrays of titania nanotubes were determined by small-angle neutron scattering and scanning electron microscopy techniques. Transmission electron microscopy and electron diffraction studies of single-standing nanotubes revealed the presence of nanocrystalline titanium oxide phases with oxidation states lower than +4 (TiO, Ti2O3). Several assumptions on growth and self-organization mechanism of nanotube arrays have been made.

The electron doped manganite system, Bi0.125Ca0.875MnO3, exhibits large bulk magnetization of unknown origin. To select amongst possible magnetic ordering models, we have conducted temperature and magnetic field dependent small-angle neutron scattering measurements. Nontrivial spin structure has been revealed. Ferromagnetic spin clusters form in the antiferromagnetic background when temperature is decreased to Tc~108K. With a further reduction in temperature or the application of external magnetic field, the clusters begin to form in larger numbers, which gives an overall enhancement of magnetization below Tc.

We report the small angle polarized neutron scattering study of nickel inverse opals, prepared by templating colloidal crystals made of polystyrene microspheres.

Polarized small-angle neutron scattering (SANS) technique is used to study spatially ordered one-dimensional (ID) magnetic nanowires. In our experiments a typical q-dependence consists of the diffuse small-angle scattering and the Bragg peak corresponding to the scattering on the regular structure of the porous matrix. We measured the total (nuclear and magnetic) scattering and the nuclear–magnetic interference as a polarization-dependent part of the scattering. The field- and temperature-dependent scattering intensity is extracted as I{H,T}(q)=I(q,H,T)−I(q,0,TR). It is shown that the magnetic scattering I{H,T}(q), obtained from the polarization-independent part, brings new and principally different information as compared to the interference term ΔI(q). We present Co embedded into mesoporous aluminosilicate matrices (MAS) as an example of investigations of the spatially ordered one-dimensional magnetic nanosystems.

ADVERTISEMENT RETURN TO ISSUEPREVNoteNEXTPhase Behavior of Binary Blends of Chemically Different, Symmetric Diblock CopolymersChristine M. Papadakis, Peter Busch, Roland Weidisch, Helmut Eckerlebe, and Dorthe PosseltView Author Information Fakultät für Physik und Geowissenschaften, Universität Leipzig, Linnéstrasse 5, D-04103 Leipzig, Germany; Institut für Werkstoffwissenschaft, Martin-Luther-Universität Halle-Wittenberg, D-06099 Halle, Germany; Institut für Werkstoffforschung, GKSS Forschungszentrum Geesthacht GmbH, Max-Planck-Strasse, D-21502 Geesthacht, Germany; and IMFUFA (Department of Mathematics and Physics), Roskilde University, P.O. Box 260, DK-4000 Roskilde, Denmark Cite this: Macromolecules 2002, 35, 24, 9236–9238Publication Date (Web):October 16, 2002Publication History Received19 February 2002Published online16 October 2002Published inissue 1 November 2002https://doi.org/10.1021/ma020269yCopyright © 2002 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views179Altmetric-Citations6LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (98 KB) Get e-AlertsSUBJECTS:Chemical structure,Copolymers,Interfaces,Order,Thickness Get e-Alerts

Elementary volume phase holograms can be recorded in poly(methyl methacrylate) doped with a photoinitiator using a holographic two-beam set-up. The photopolymerization process of the residual monomers in the polymer matrix turns out to be inherently non-linear. Consequently, illumination with a sinusoidal light intensity pattern results not only in a grating with the fundamental spatial frequency but also with higher harmonics. As the absorption of the photodoped material steeply rises for wavelengths below 320 nm, structures with periods below about 105 nm cannot be read out by light diffraction in Bragg geometry, the limit for Laue geometry is even 160 nm. This poses the following question: Can we induce gratings by light which are below the optical resolution limit by the non-linear recording mechanism and how can we prove it?

Illumination of photosensitized (PMMA) with light triggers nonlinear polymerization processes. this way periodical density structures with nearly 10(4) lines/mm can be generated which are beyond the resolution limit of light-optical investigation methods. We report on the first direct experimental observation of such higher harmonics in deuterated (PMMA) by the nondestructive method of diffraction of neutrons at a wavelength of 1.2 nm. Diffraction efficiency of the second harmonic was found to be 200-500 times weaker than that of the first order. The origin of higher harmonics is attributed to the nonlinearities of the processes of chain growth and of termination.