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angle  bilayers  boundaries  crystal  diffraction  dislocations  high  instruments  low  neutron  nsbbf  single  thermal conductivity  thermal 
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Preview: Journal of Applied Crystallography

Journal of Applied Crystallography

Journal of Applied Crystallography covers a wide range of crystallographic topics from the viewpoints of both techniques and theory. The journal presents articles on the application of crystallographic techniques and on the related apparatus and computer

Published: 2018-02-21


Neutron diffraction from aligned stacks of lipid bilayers using the WAND instrument


Neutron diffraction from aligned stacks of lipid bilayers is examined using the Wide-Angle Neutron Diffractometer (WAND), located at the High Flux Isotope Reactor, Oak Ridge, Tennessee, USA. Data were collected at different levels of hydration and neutron contrast by varying the relative humidity (RH) and H2O/D2O ratio from multi-bilayers of dioleoylphosphatidylcholine and sunflower phosphatidylcholine extract aligned on single-crystal silicon substrates. This work highlights the capabilites of a newly fabricated sample hydration cell, which allows the lipid bilayers to be hydrated with varying H/D ratios from the RH generated by saturated salt solutions, and also demonstrates WAND's capability as an instrument suitable for the study of aligned lipid multi-bilayers.

The suite of small-angle neutron scattering instruments at Oak Ridge National Laboratory


Oak Ridge National Laboratory is home to the High Flux Isotope Reactor (HFIR), a high-flux research reactor, and the Spallation Neutron Source (SNS), the world's most intense source of pulsed neutron beams. The unique co-localization of these two sources provided an opportunity to develop a suite of complementary small-angle neutron scattering instruments for studies of large-scale structures: the GP-SANS and Bio-SANS instruments at the HFIR and the EQ-SANS and TOF-USANS instruments at the SNS. This article provides an overview of the capabilities of the suite of instruments, with specific emphasis on how they complement each other. A description of the plans for future developments including greater integration of the suite into a single point of entry for neutron scattering studies of large-scale structures is also provided.

Structural evolution of a Ge-substituted SnSe thermoelectric material with low thermal conductivity


Thermoelectric materials are expected to become new alternative sources of sustainable energy. Among them, the SnSe intermetallic alloy has been described as an excellent thermoelectric compound, characterized by an extremely low thermal conductivity with maximum performance at the onset of a structural phase transition at 800 K. Recently, novel SnSe derivatives with Ge substitution have been synthesized by a direct arc-melting technique. This produces nanostructured polycrystalline samples that exhibit a record high Seebeck coefficient, anticipating an excellent performance above room temperature. Here, the structural phase transition from a GeS-type structure (space group Pnma) to a TlI-type structure (space group Cmcm) is investigated in situ via neutron powder diffraction (NPD) in the temperature range 298–853 K for the selected composition Sn0.8Ge0.2Se. This transition takes place at 803 K, as shown by differential scanning calorimetry. The analysis from the NPD data shows a non-monotonic behaviour of the anisotropic displacement parameters upon entering the domain of the Cmcm structure. The energies of the atomic vibrations have been quantitatively analysed by fitting the temperature-dependent mean-square displacements to Einstein oscillators. The thermal conductivity of Sn0.8Ge0.2Se is as low as 0.35 W m−1 K−1 at 773 K, which mostly represents the lattice thermal contribution.

Origin of the superstructure elucidated by atomic resolution HAADF-STEM and HREM in the Ce10W22O81 lanthanide tungstate phase


The present paper provides new information on the attribution of the cationic sites of the orthorhombic Ce10W22O81 crystal phase prepared in the CeO2–Ce2O3–WO3 ternary system. Atomic resolution HAADF-STEM (high-angle annular dark-field scanning transmission electron microscopy) and HREM (high-resolution electron microscopy) investigations have highlighted the presence of two mixed columns of Ce and W cations along the a axis that were previously assigned to pure W cations in the asymmetric unit. This discovery explains the presence of a commensurate superstructure doubling the orthorhombic unit-cell length ao.

Single-crystal neutron diffraction in diamond anvil cells with hot neutrons


It is demonstrated that it is possible to perform single-crystal measurements in diamond anvil cells (DACs) with a monochromatic beam at modern hot neutron sources that offer the benefit of short neutron wavelengths with high fluxes. A piston–cylinder DAC with conical Boehler–Almax diamonds that allows for a wide accessibility of the reciprocal space has been developed. The diffraction data collected in this cell using hot neutrons are of very good quality and can be used for a full and reliable structure refinement.

Thermo-physical properties of a new UV nonlinear optical crystal: NaSr3Be3B3O9F4


NaSr3Be3B3O9F4 (NSBBF) as a new UV nonlinear optical crystal has aroused great interest in recent years. This study investigates the thermo-physical properties of NSBBF, including thermal expansion, thermal diffusivity, thermal conductivity and specific heat, which are important parameters for applications. The specific heat of NSBBF is comparable to that of CsLiB6O10 (CLBO) and larger than that of β-BaB2O4 (β-BBO), indicating that NSBBF has a very high laser damage threshold. The thermal expansion coefficients of NSBBF are determined as αa = 1.05 × 10−5 K−1 and αc = 1.34 × 10−5 K−1, exhibiting much smaller anisotropy than those of CLBO and β-BBO. The thermal diffusivity and conductivity of NSBBF are also obtained in the temperature region from 323 to 573 K, showing comparable anisotropies to β-BBO. All these results show that NSBBF is suitable for high-power UV laser generation.

Low-angle boundaries in ZnGeP2 single crystals


The structure of low-angle boundaries in ZnGeP2 crystals grown by the vertical Bridgman technique was studied using Borrmann X-ray topography. The slip systems of the dislocations in the boundaries were identified by studying the contrast rosettes generated by the Borrmann effect, in the region near the dislocation core. It was shown that the boundaries are of two types: type I consists of edge dislocations of the {1\overline{1}0}〈110〉 slip system, and type II of edge and mixed dislocations of the {010}〈100〉 slip system. The boundaries of both types, consisting of pure edge dislocations with lines along [001], are symmetrical tilt boundaries with [001] rotation axes. The misorientations generated by the boundaries were estimated to range between 2–20 and 1–40′′, respectively. Low-angle boundaries are thought to be formed by polygonization of dislocations, caused by thermoelastic stresses.

How to distinguish between opposite faces of an a-plane sapphire wafer


A method to distinguish between two symmetrically equivalent opposite (11{\overline 2}0) and ({\overline 1}{\overline 1}20) faces of an a-plane sapphire wafer is described. It is shown that use of conventional X-ray diffraction analysis makes it possible to determine the `sign' of the sapphire a face in contrast to the `sign' of the c, m or r faces. Correct determination of the a-plane wafer orientation is important for further growth and processing of heteroepitaxial structures.

System for in situ observation of three-dimensional structural changes in polymer films during uniaxial deformation. Corrigendum


Ambiguities in the article by Miyazaki, Shimokita, Ogawa & Yamamoto [J. Appl. Cryst. (2015), 48, 1016–1022] are clarified.