M. Wolff  J. Herbel  F. Adlmann  A. J. C. Dennison  G. Liesche  P. Gutfreund  S. Rogers 《Journal of Applied Crystallography》2014,47(1):130-135

Small‐angle scattering in grazing‐incidence beam geometry has been applied on a time‐of‐flight neutron instrument to investigate a solid–liquid boundary. Owing to the broad wavelength distribution provided for a specific incident beam angle, the penetration depth of the neutron beam is varied over a wide range in a single measurement. The near surface structures of block copolymer micelles close to silicon substrates with distinct surface energies are resolved. It is observed that the very near surface structure strongly depends on the surface coating, whereas further away from the surface, bulk‐like ordering is found.  相似文献   

    

Arthur J. Schultz  Mads Ry Vogel Jrgensen  Xiaoping Wang  Ruth L. Mikkelson  Dennis J. Mikkelson  Vickie E. Lynch  Peter F. Peterson  Mark L. Green  Christina M. Hoffmann 《Journal of Applied Crystallography》2014,47(3):915-921

The intensity of single‐crystal Bragg peaks obtained by mapping neutron time‐of‐flight event data into reciprocal space and integrating in various ways is compared. These methods include spherical integration with a fixed radius, ellipsoid fitting and integration of the peak intensity, and one‐dimensional peak profile fitting. In comparison to intensities obtained by integrating in real detector histogram space, the data integrated in reciprocal space result in better agreement factors and more accurate atomic parameters. Furthermore, structure refinement using integrated intensities from one‐dimensional profile fitting is demonstrated to be more accurate than simple peak‐minus‐background integration.  相似文献   

    

Tae‐Hwan Kim  Young‐Soo Han  Jong‐Dae Jang  Baek‐Seok Seong 《Journal of Applied Crystallography》2014,47(1):53-59

In the temperature range of 303–333 K, the self‐assembled structures of a mixture of Pluronic F127 triblock copolymer [PEO₁₀₆PPO₇₀PEO₁₀₆; PEO is poly(ethylene oxide) and PPO is poly(propylene oxide)] and an organic derivative, 5‐methyl salicylic acid (5mS), in aqueous solution have been investigated using small‐angle neutron scattering (SANS). Above a 5mS concentration of 1.93 g l⁻¹, the F127–5mS mixture solution became cloudy with a blue colour arising from the Tyndall effect, indicating that large polymer aggregates had formed in the mixture solution. SANS measurements showed that the self‐assembled structure of the F127–5mS mixture transformed from a spherical to a cylindrical micelle with increasing the concentration of 5mS in the temperature range of 303–323 K. When the 5mS concentration was increased to 3.3 g l⁻¹, the self‐assembled structure of the F127–5mS mixture at 333 K underwent an additional phase transition from a cylindrical to a spherical micelle of large size at a 5mS concentration of 2.75 g l⁻¹, although its self‐assembled structure changed from a spherical to a cylindrical micelle at a 5mS concentration of 1.93 g l⁻¹ as well. The phase transitions are explained by the variation of the mass fraction of the hydrophilic part of F127 and the coupled effect of the limited solubility and the strong tendency to bind with amphiphilic molecules of 5mS. Using a simple material balance equation and the structural information obtained from SANS model analyses, the numbers of D₂O and of 5mS molecules in the core and corona regions are calculated. This result can provide a simple and easy way to prepare various nanostructures using a Pluronic triblock copolymer in aqueous solution and may be very useful for practical applications of a Pluronic polymer such as various nanobuilding blocks or nanotemplates.  相似文献   

    

Alex Lindsay‐Scott  David Dobson  Fabrizio Nestola  Matteo Alvaro  Nicola Casati  Christian Liebske  Kevin S. Knight  Ronald I. Smith  Ian G. Wood 《Journal of Applied Crystallography》2014,47(6):1939-1947

Using the recently upgraded Polaris diffractometer at the ISIS Spallation Neutron Source (Rutherford Appleton Laboratory), the crystal structures of the post‐perovskite polymorphs of NaCoF₃ and NaNiF₃ have been determined by time‐of‐flight neutron powder diffraction from samples, of mass 56 and 16 mg, respectively, recovered after synthesis at ∼20 GPa in a multi‐anvil press. The structure of post‐perovskite NaNiF₃ has also been determined by single‐crystal synchrotron X‐ray diffraction for comparison. All measurements were made at atmospheric pressure and room temperature. Despite the extremely small sample size in the neutron diffraction study, there is very good agreement between the positional parameters for NaNiF₃ obtained from the refinements of the X‐ray and neutron data. Relative to the commonly used oxide post‐perovskite analogue phases having calcium as the A cation, the axial ratios and derived structural parameters of these fluoride post‐perovskites are more consistent with those of Mg_0.91Fe_0.09SiO₃ at high pressure and temperature. The structures of NaCoF₃ and NaNiF₃ are very similar, but the unit‐cell and CoF₆ octahedral volumes of NaCoF₃ are larger than the corresponding quantities in NaNiF₃, which supports the hypothesis that the Co²⁺ ion has a high‐spin state in this compound. The anisotropic atomic displacement parameters of the Na ions in NaNiF₃ post‐perovskite are of similar magnitude to those of the F ions. The probability ellipsoid of the F1 ion is a prolate spheroid with its largest component parallel to the b axis of the unit cell, corresponding to rotational motion of the NiF₆ octahedra about the a axis of the crystal. Although they must be synthesized at pressures above about 18 GPa, these ABF₃ compounds are strongly metastable at atmospheric pressure and room temperature and so are highly suitable for use as analogues for (Mg,Fe)SiO₃ post‐perovskite in the deep Earth, with significant advantages over oxides such as CaIrO₃ or CaPtO₃.  相似文献   

    

David F. R. Mildner 《Journal of Applied Crystallography》2014,47(4):1247-1251

A small‐angle neutron scattering instrument that uses a reflective focusing optic can achieve smaller values of the scattering vector, and with higher resolution, than the usual pinhole collimation. When the focusing mirror images the source onto the detector, the analytic expression for the resolution is independent of the sample area and is principally determined by the beam divergence incident on the sample, modified by the distance between the optic and the sample. The results are applied to a focusing SANS instrument with axisymmetric mirrors.  相似文献   

    

D. Mukherji  R. Gilles  L. Karge  P. Strunz  P. Beran  H. Eckerlebe  A. Stark  L. Szentmiklosi  Z. Mcsik  G. Schumacher  I. Zizak  M. Hofmann  M. Hoelzel  J. Rsler 《Journal of Applied Crystallography》2014,47(4):1417-1430

Nickel‐based superalloys are the materials of choice in the hot section of current gas turbines, but they are reaching temperature limits constrained by their melting temperature range. Co–Re alloy development was prompted by a search for new materials for future gas turbines, where the temperature of application will be considerably higher. Addition of the very high melting point refractory metal Re to Co can increase the melting range of Co alloys to much higher temperatures than the commercial Co alloys in use today. The alloy development strategy is first discussed very briefly. In this program, model ternary and quaternary compositions were studied in order to develop a basic understanding of the alloy system. In situ neutron and synchrotron measurements (small and wide angle) at high temperatures were extensively used for this purpose and some selected results from the in situ measurements are presented. In particular, the effect of boron doping in Co–Re–Cr alloys and the stability of the TaC precipitates at high temperatures were investigated. A fine dispersion of TaC precipitates strengthens some Co–Re alloys, and their stability at the application temperature is critical for the long‐term creep properties.  相似文献   

    

Carlos A. Lpez  Jos C. Pedregosa  Diego G. Lamas  Jos A. Alonso 《Journal of Applied Crystallography》2014,47(4):1395-1401

The crystal structure and ionic conductivity properties of a novel microcrystalline Sr₁₁Mo₄O₂₃ ceramic material are presented. This material has been prepared by thermal treatment up to 1473 K, in air, of previously decomposed citrate precursors. The complex crystal structure was refined from combined X‐ray powder diffraction and neutron powder diffraction data. The formula of this phase can be rewritten as Sr_1.75□_0.25SrMoO_5.75, highlighting the relationship with double perovskites A₂B′B′′O₆. At room temperature, the crystal structure is tetragonal in space group I4₁/a, with a = 11.6107 (6) Å, c = 16.422 (1) Å and V = 2213.8 (2) ų. The crystal network contains O anion and Sr cation vacancies. The structure is complex, with Sr, Mo and O atoms distributed over four, two and six distinct Wyckoff sites, respectively. Only one of the Sr sites (SrO₆) corresponds to the octahedral network; one of the two MoO₆ types of octahedra is axially distorted. The three other Sr positions occupy the A site with higher coordination. There is an occupational deficit of O atoms of 22 (4)%. This defective framework material presents an interesting ionic mobility, enhanced above 773 K owing to a further reduction in the oxygen content.  相似文献   

    

Pavol Mikula  Miroslav Vrna  Jan Pilch  Baek Seok Seong  Wanchuck Woo  Vyacheslav Em 《Journal of Applied Crystallography》2014,47(2):599-605

The neutron diffraction properties of a double‐crystal (+n,−m) setting, which contains a bent perfect Si(311) crystal in the fully asymmetric diffraction (FAD) geometry with output beam expansion and a bent perfect Si(220) crystal in the symmetric diffraction geometry, are presented. Generally, there are two possibilities for the FAD geometry: either with output beam compression or with output beam expansion. In this case, attention has been focused on the latter. The properties of the (+n,−m) double‐bent‐crystal arrangement of a bent perfect crystal FAD Si(311) geometry, in combination with a bent Si(220) crystal slab in the symmetric diffraction geometry, were studied. It was found that, after beam expansion, this FAD geometry can provide a monochromatic beam of rather large cross section but very small divergence.  相似文献   

    

Man‐Ho Kim  Jeong‐Mann Doh  Seong Chul Han  Keun Hwa Chae  Byung‐Yong Yu  Kyung Tae Hong  Andrew Jackson  Lawrence M. Anovitz 《Journal of Applied Crystallography》2011,44(6):1238-1245

The structure of porous TiO₂ prepared by electrochemical anodization in a fluoride‐containing ethylene glycol electrolyte solution was quantitatively studied using small‐angle neutron scattering (SANS) and ultra‐small‐angle neutron scattering (USANS). The cylindrical pores along the coaxial direction were somewhat irregular in shape, were widely distributed in diameter, and seemed to have a broadly pseudo‐hexagonal arrangement. The scattering from the pore wall showed a negative deviation from Porod scattering, indicating that the interface between TiO₂ and the pore was not sharp. A density gradient of around 40–60 Å at the pore wall (i.e. the interface between the pore and the TiO₂ matrix) was estimated using both constant and semi‐sigmoidal interface models. This gradient may be due to the presence of fluorine and carbon partially absorbed by the pore wall from the fluoride‐containing electrolyte or to sorbed water molecules on the wall. The neutron contrast‐matching point between the TiO₂ matrix and the pores filled with liquid H₂O/D₂O mixtures was 51/49%(v/v) H₂O/D₂O, yielding an estimated mass density of 3.32 g cm⁻³. The specific surface area of the sample derived from the (U)SANS data was around 939–1003 m² cm⁻³ (283–302 m² g⁻¹).  相似文献   

    

Dazhi Liu  Kunlun Hong  Carrie Y. Gao  Yuri Melnichenko  Ken Littrell  Greg Smith  Jinkui Zhao 《Journal of Applied Crystallography》2011,44(5):1120-1122

Initial experimental results are reported from the extended Q‐range small‐angle neutron scattering (EQ‐SANS) diffractometer at the Spallation Neutron Source at Oak Ridge National Laboratory (ORNL). A generation‐8 polyamidoamine dendrimer was measured and the conformation parameters (radius of gyration, thickness of the soft shell etc.) extracted by model fitting to the scattering data. The results are compared with data collected at the general‐purpose small‐angle neutron scattering (GP‐SANS) beamline at the High‐Flux Isotopic Reactor at ORNL and show that EQ‐SANS is ready for scientific studies for the small‐angle neutron scattering community.  相似文献