bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of Pd-based Tsai-type 1/1 approximants
Authors: Fukami Reiko , Hiroto Takanobu , Tamira Ryuji
Published: November 2015

Recently, a new Tsai-type 1/1 approximant (AP) was discovered in the Pd-Ge-Yb system by Kashimoto et al[1]. In this alloy, the Yb valence was found to be in an intermediate state between Yb2+ and Yb3+. On the other hand, various magnetic transitions were found in other rare-earth (RE) bearing Tsai-type APs. In this work, the formation condition and magnetic property of Pd-M-RE appximants were investigated. Mother ingots of various conditions based on Pd-M-Yb[1], were prepared by arc melting followed by various heattreatment conditions to obtain homogeneous equilibrium phases. The Phase constitutions were studied by powder X-ray diffraction (XRD). The obtained XRD patterns can be indexed as 1/1 AP. The details of the formation conditions as well as magnetic properties will be presented in the poster.
Optical conductivity of the R-Cd quasicrystals and approximants
Authors: Armstrong Nathan , Mortimer Kevin , Kong Tai , Movassagh M. Rahimi , Budko Sergey , Canfield Paul , Timusk Thomas
Published: November 2015

Recently, a new family of R-Cd binary icosahedral quasicrystals has been discovered [1]. Using optical reflectance spectroscopy, we have examined the quasicrystal GdCd7.98and the approximants GdCd6and YCd6. To explain the unique behaviour of electrons in a quasiperiodic lattice Mayou [2] created a model of electron transport due to anomalous diffusion of wave packets scattering from the quasiperiodic lattice. We have determined the optical conductivity of the above-mentioned materials from 7.5 meV to 5.5 eV and have used Mayou's model of optical conductivity for approximants and quasicrystals, σ1∝ Re[ (1/(γ-iω))^(2β-1) ], to describe the low frequency behaviour. Despite the concern of Mayou of not being able to differentiate experimentally between normal metallic conductivity of ballistic electrons, β=1, and sub-ballistic conductivity, 1/2<β<1, we clearly see β≍3/4 in the intraband peak of the icosahedral approximants, which has not been observed before. Before this work, the only unambiguously Drude-like peak seen in any quasicrystal or their approximant occurred in the decagonal approximant γ-brass, which was fit with exactly β=1 [3]. However, unlike the approximants in our study, this sample of γ-brass was admittedly not a good approximant to a quasicrystal with its small lattice constant. In the GdCd7.98quasicrystal, we observe low frequency behaviour that lacks a Drude peak but is not nearly perfectly linear as seen by others. In this case, the low frequency behaviour is qualitatively similar to the diffusive regime, 0<β<1/2, that is often seen. However, it is not adequately modelled by Mayou's generalized Drude model. With these results, unlike in previous optical conductivity studies, we have a striking difference in the low frequency conductivity that suggests that there is a difference in the physics of the optical conductivity of periodic and quasiperiodic lattices that needs to be explored.
2D quasicrystals from perovskites
Authors: Förster Stefan , Zollner Eva , Meinel Klaus , Hammer Renè , Trautmann Martin , Widdra Wolf
Published: November 2015

Perovskite oxides represent a versatile class of materials with a simple cubic or pseudo-cubic crystal structure. The family of perovskite oxides contains insulators, metals, semiconductors, and superconductors with nearly identical lattice parameters. This structural equivalence additionally allows to combine perovskites with different properties in multilayer systems to produce functional materials with unique properties. We report here on the formation of a quasicrystal (QC) thin film on a threefold Pt(111) surface. This QC film is derived from the classical perovskite oxide BaTiO3 which is the most intensely studied ferroelectric perovskite oxide. An easily accessible ferroelectric to paraelectric phase transition at 400 K makes the material so interesting for basic and applied research. Due to matching lattice conditions BaTiO3 can be grown epitaxially on selected metal substrates. Periodic thin films of either BaTiO3(100) or BaTiO3(111) have been grown depending on substrate orientation and preparation conditions on Pt(001) and on Pt(111) [1, 2]. As we demonstrate here, astonishingly also a two-dimensional dodecagonal quasicrystalline structure can be formed by annealing an initially 1.4 nm thick BaTiO3 film on Pt(111) [3]. It develops at a temperature of 1250 K from a wetting layer spreading between a few thicker BaTiO3(111) islands. Surface sensitive electron diffraction (LEED) shows a bright and sharp pattern with dodecagonal symmetry. High-resolution scanning tunneling microscopy (STM) images reveal an arrangement of quadratic, triangular, and rhombic elements which compares well to a Gähler tiling. The development of higher-order self-similar structures is widely suppressed by a linear phason strain. This is supported by the fine structure of the diffraction data.
Crystal structure refinement of MgSiO3high temperature C2/c clinoenstatite
Authors: Yoshiasa Akira , Nakatsuka Akihiko , Okube Maki , Katsura Tomoo
Published: November 2015

The high-temperature clinoenstatite (HT-CEn) is one of the important MgSiO3 pyroxene polymorph. The single-crystal of C2/c HT-CEn endmember is firstly synthesized by rapid pressure-temperature quenching from 15-16 GPa and 900-19000C [1]. No report that it is produced as single crystal or large domain has been made on the MgSiO3 endmember. The HT-CEn-type modifications are observed in Ca-poor Mg-Fe clinoenstatite and pigeonite and are always found to be unquenchable in rapid cooling. The high pressure and high temperature experiments of MgSiO3 composition were carried out with a Kawai-type multi-anvil apparatus. The samples were quenched by rapidly releasing the oil pressure load and/or by blow out of anvil cell gasket. The space group of C2/c is strictly determined by Rigaku RAPID Weissenberg photographs and synchrotron radiation. Single-crystal X-ray diffraction experiments were performed at ambient conditions using a Rigaku AFC-5 four circle diffractometer. A total of 9383 reflections was measured and averaged in Laue symmetry 2/m to give 766 independent reflections used for the structure refinements. Final reliability factors converged smoothly to R = 0.029. The single-crystal diffraction analysis shows that the unusual bonding distances frozen in this metastable structure. The degree of kinking of the silicate tetrahedral chains is 1750for HT-CEn. The chain angle for HP-CEn is substantially smaller (1350) and the angle for L-CEn turned to the opposite direction at -1600(=2000). The degree of kinking increases by being curved in more than 1800in the transition from HT-CEn to L-CEn. As for the reverse change from the expansion to the stretch, a potential barrier exists in the point of the continuity. It is suggested that the reason which can quench structure under ambient conditions is the present HT-CEn single crystal was formed by the isosymmetric phase transition from HP-CEn. HT-CEn type single-crystals cannot be frozen without pressure.
Diffraction Studies of Tungsten Bronze Type Relaxor Ferroelectrics
Authors: Whittle Thomas , Schmid Siegbert
Published: November 2015

Ferroelectric materials are essential for modern electronic applications, from consumer electronics to sophisticated technical instruments. Relaxor ferroelectric materials provide the advantage of high dielectric constants over broad temperature ranges not seen in traditional ferroelectrics. Tungsten bronze type compounds have been shown to display a variety of industrially relevant optical and electronic properties amongst others. There is a fundamental relationship between the physical properties displayed by ferroelectrics and the crystal structures in which they form. Of particular interest are compositions and temperatures near phase transition. These are import because near phase transitions, particularly morphotropic phase transitions, electromechanical properties are often dramatically enhanced. [1,2] This work focuses on the structural investigation of the tungsten bronze type relaxor ferroelectric materials in the BaxSr3-xTi1-yZryNb4O15 (0 ≤ x ≤ 3; 0 ≤ y ≤ 1) system. A combination of X-ray, neutron (ToF and constant wavelength) and electron diffraction were employed to map the entire room temperature phase space. In addition, morphotropic phase boundary compositions were determined accurately. Variable temperature synchrotron X-ray diffraction studies were utilised to further explore the phase diagram for non-ambient conditions. Temperature dependent phase transitions were determined and the relationship between composition and transition temperature analysed. Structural models used in this work resulted from Rietveld refinements against powder diffraction data. [3] This work will shed light on new lead free relaxor ferroelectric materials.
Substitution Effects of Gd and Mg on Cubic Structure of Barium Titanate
Authors: Takeda Shoichi , Yasuda Satoshi , Moriyoshi Chikako , Kuroiwa Yoshihiro , Honda Atsushi , Inoue Noriyuki , Higai Shin'ichi , Ando Akira
Published: November 2015

Barium titanate BaTiO3 is a ferroelectric oxide with low dielectric loss and high permittivity, which makes it a good insulator for industrial uses. However, the pure barium titanate is not always used for electronic devices. Gd- and Mg-doping in barium titanate is effective for the dielectrics in multilayer ceramic capacitors MLCCs, for example, to attain the uniform temperature-variation of dielectric constants in the wide temperature-range where MLCCs are practically used, while the Curie temperature is significantly decreased [1]. In this study, the structural characteristics of Gd- and Mg-substituted barium titanate (Ba,Gd)(Ti,Mg)O3 (BGTM) in the cubic phase were investigated to clarify the effects of Gd- and Mg-substitution on the crystal structure and the chemical bonding. Synchrotron radiation x-ray powder diffraction measurements were carried out using the BGTM samples with the Mg content of x = 0 ~ 0.1. Lattice parameters, substitution sites of the Gd and Mg ions, thermal parameters, and electron charge density distributions in the crystals were analyzed by using the maximum entropy method (MEM)/Rietveld method. The Curie temperature decreased with increasing x. The phase transition did not take place in BGTM with x > 0.05. The Gd ion was confirmed to be substituted for the Ba ion with larger thermal vibration amplitude than that of the Ba ion. The amplitude was almost independent of the Gd content. It was revealed that the Gd ion occupied the off-centered positions slightly form the Ba-site along the <100> directions at lower temperatures. Difference in thermal behaviors of the Gd and Ba ions can be attributed to the size difference between the smaller Gd ion and the larger Ba ion. The Mg ion was observed on the Ti-site. The substitution of the Mg ion for the Ti ion suppresses the ferroactivity of the Ti ion, which causes the lowering of the Curie temperature.
Petalite Under Pressure
Authors: Ross Nancy , Zhao Jing , Spencer Elinor , Slebodnick Carla , Chakoumakos Bryan
Published: November 2015

The lithium aluminosilicate mineral petalite (LiAlSi4O10) has been studied using high-pressure single-crystal X-ray diffraction up to 5 GPa. Petalite is a layered silicate mineral. The layers comprise puckered double-sheets of corner-sharing SiO4tetrahedra. Corner-sharing AlO4tetrahedra bridge neighboring layers and complete the 3D architecture. The charge is balanced by lithium cations that reside within channels that propagate through the structure. Petalite undergoes two pressure-induced phase transitions at ca. 1.5 and 2.5 GPa. The first of these transforms the low-pressure α-phase of petalite (P2/c) to an intermediate β′ phase that then fully converts to the high-pressure β phase at ca. 2.5 GPa. The α→β transition is isomorphic with a commensurate modulation that triples the unit cell volume. Measurement of the unit cell parameters of petalite as a function of pressure, and fitting of the data with 3rd order Birch-Murnaghan equations of state, has provided revised elastic constants for petalite. The bulk moduli of the α- and β-phases are 49(1) and 35(3) GPa, respectively. These values indicate that petalite is one of the most compressible lithium aluminosilicate minerals. The α-phase structure has been refined at five different pressures, revealing a compression mechanism that is driven by the rigid body movement of the Si2O7units from which the silicate double-layers are constructed. The structure of the β′ phase was not determined. The structure of the β phase was determined at 2.71 GPa. Although the fundamental structural features of petalite are retained in the α → β phase transition, subtle alterations occur in the internal structure of the silicate double-layers.
Two types of adjacent dimer layers in the low-temperature phase of BaCuSi2O6
Authors: Sheptyakov Denis , Pomjakushin Vladimir , Stern Raivo , Heinmaa Ivo , Nakamura Hiroyuki , Kimura Tsuyoshi
Published: November 2015

The low-temperature crystal structure of BaCuSi2O6has been investigated with high-resolution synchrotron x-ray and neutron powder diffraction techniques and has been found to be on average (ignoring the incommensurate modulation) orthorhombic, with the most probable space group Ibam. The Cu-Cu dimers in this material are forming two types of layers with distinctly different interatomic distances. Subtle changes also modify the partially frustrated interlayer Cu-Cu exchange paths. The present results corroborate the interpretation of low-temperature nuclear magnetic resonance and inelastic neutron scattering data in terms of distinct dimer layers. The experimentally determined low-temperature crystal structure of BaCuSi2O6is discussed in terms of its relation to the newer findings of theory and of the complementary experiments.
Phase Transitions in Borohydride Perovskites
Authors: Schouwink Pascal , Cerny Radovan
Published: November 2015

A series of complex hydrides based on the highly dynamic tetrahydroborate anion BH4-and crystallizing in theABX3type lattice has recently been discovered. They present a rare case of a family of iono-covalent hydrides that has a genuine tunable host lattice, making them an interesting new class of host compounds for not only the design of hydrogen storage materials but also hydride-properties related to heavy metals. Amongst these, preliminary results onREE-based luminescence will be discussed in the neat and doped compounds, the Ln2+excited states surprisingly not being subject to significant quenching by B-H vibrations. Unlike oxide- or halide-perovskites some members of theAB(BH4)3group do not evolve to higher symmetries as a function of temperature. We show by means ofin-situsynchrotron X-ray powder diffraction, vibrational spectroscopy andab initiocalculations in the solid state, that temperature-induced structural distortions in perovskite-typeACa(BH4)3(A= K, Rb, Cs) have their origin in close hydridic di-hydrogen contacts of repulsive nature. Coupling between internal B-H vibrations and phonons results in lattice distortions that are identical in symmetry to well-known instabilities (soft modes) in perovskites, which generally condense to lower temperatures. Anion-substitution BH4-<->X-(X= Halide) calculated on ordered models can relax distortions caused by repulsive effects. High temperature phase-transitions inACa(BH4)3can be of first or second-order, including 2-fold superlattices, simple cubic-cubic transitions accompanied by volume expansion or complex modulated superstructures accompanied by negative volume expansion, as is the case in RbCa(BH4)3. Close di-hydrogen contacts may be suggested as a tool to tailor the crystal symmetry in complex hydride perovskites in the future.
Investigation of thermally induced phase transitions in uranium perovskites
Authors: Reynolds Emily , Kennedy Brendan
Published: November 2015

The physical properties of inorganic solids are intimately related to their crystal structures and there is increasing awareness of the potential importance of metastable structures that exist over a limited temperature and/or pressure range. For the renaissance of nuclear energy to continue it is vital to improve the efficiency and safety of the nuclear fuel process. In order to do this, a comprehensive knowledge of the fundamental chemical, structural, and thermodynamic properties of uranium compounds is required. Compounds of the type A2BUO6 (A = Ba, Sr; B = Ba, Sr, Ca) have been prepared and characterised using neutron and X-Ray diffraction techniques as well as X-ray absorption spectroscopy. For the first time the high temperature behaviour of these complex oxides has been investigated, and as illustrated by Ba2SrUO6, heating such oxides can induce a sequence of phase transitions with the structure of Ba2SrUO6 changing from monoclinic in P21/n at room temperature to cubic in Fm-3m above 1200 K. [1] The compounds Ba2CaUO6 and BaSrCaUO6 were also found to undergo a series of thermally induced phase transitions from the P21/n monoclinic structure. In order to elucidate the structural changes involved in each system, a combination of diffraction techniques was required. We also utilised symmetry-mode analysis in which the structures are refined in terms of the fundamental tilting modes. This elegant way of tracking phase transitions provided vital insight when comparing and contrasting the thermal behaviour of these complex uranium oxides.
Origin of surface impurities on the Cave of Swords selenite crystals at Naica
Authors: Montero-Cabrera Maria Elena , Castillo-Sandoval Isai , Fuentes-Cobas Luis , Esparza-Ponce Hilda , Fuentes-Montero Maria Elena , Carreño-Marquez Ivan Jalil , Reyes-Cortes Manuel
Published: November 2015

The Cave of Swords was discovered in 1910 at Naica mine, Chihuahua, Mexico. Its name refers to the look of the 1-2 m long crystals the cave had when it was discovered. Currently the crystals are 0.1-0.3 m long. The crystals surface is opaque and ocher. For over 100 years these crystals continue to amaze and give us clues about their formation. This work is part of a research aimed at the conservation of the Naica Giant Crystals. Thirteen samples from the Cave of Swords were analyzed by Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS), Confocal Laser Microscopy with Differential Interference Contrast (LCM-DIM) and Transmission Electron Microscopy (TEM). X-Ray Fluorescence (μ-XRF) together with X-ray Absorption Near Edge Structure (μ-XANES) and X-ray Photoelectron Spectroscopy (XPS) were employed for elemental analysis. For phase analysis, X-ray diffraction (XRD) in both symmetric and grazing incidence geometries (GI-XRD) and Micro electron diffraction at TEM were used. Impurities on crystals surfaces show a heterogeneous distribution of the present elements. The thickness of impurities ranges from 120 nm to 150 μm. The phases identified were (see figure) gypsum (1, 2, 3, 6, 9, 10, 13), hematite (4, 7, 8), sphalerite (14), chalcopyrite (11), cuprite (15), galena (5), alabandite (12), halite, fluorite and amorphous Pb and Mn oxy-hydroxides. Al, C, Ca, Cl, Cu, F, Fe, Mg, Mn, Na, O, Pb, S, Si and Zn elements were identified. A model for the origin of impurities follows: Selenite stopped growing when the solution became sub-saturated. Then, hematite was deposited as the main phase, which was dissolved or suspended in the solution. Hematite matrix served for the adsorption of other crystalline and amorphous phases. We concluded that humans have not produced the impurities, which are witnesses of the gypsum crystals formation. Acknowledgment: Stanford Synchrotron Radiation Lightsource, Harvard Museum of Natural History and CONACYT CB-183706.
Correlation of macroscopic and structural properties in Piezoceramics
Authors: Hinterstein Manuel , Hoelzel Markus , Rouquette Jerome , Ehrenberg Helmut , Hoffman Mark
Published: November 2015

Piezoelectric ceramics exhibit the remarkable property to couple elastic strain and polarization under the influence of an applied electric field. Among the various types of ferroelectric devices only actuators rely on high electric fields to generate high strains and forces. Prominent examples for actuators are multilayer stack actuators used for nanopositioning or in modern combustion engines for automobiles to control injection cycles. Despite extensive studies and elaborated measurement techniques, the correlation between macroscopic strain and structural response is still not fully understood. Most of the relevant systems found up to now are compositions close to phase boundaries linking highly correlated phases. This results in major challenges for structural analyses due to overlapping reflections. Apart from the well-known field induced structural responses such as domain switching and the piezoelectric effect we recently identified field induced phase transitions in different systems as an additional poling mechanism [1,2]. In this contribution we present a structural analysis of in situ powder diffraction data that is capable of resolving all three involved poling mechanisms within only one experiment. The key to obtain enough information for such an analysis is a combination of high resolution and a broad Q-range, together with different sample orientations. This can be done with either X-ray or Neutron powder diffraction. The results not only separately reveal the contributions of each poling mechanism to the macroscopic strain, but also different behaviours of the individual phases. Several studies on lead containing as well as lead free systems showed significant changes while crossing the phase boundaries. Additionally, the calculation of the elastic strain perfectly matches the macroscopic observations, confirming the accuracy of the applied models.
Polymorphism and electronic transformations of deep Earth minerals
Authors: Dubrovinsky Leonid
Published: November 2015

While powder X-ray diffraction studies stepped over a megabar in pressure already in the 1970s, single crystal experiments remained much rarer and covered until recently a very limited pressure range barely reaching 15 GPa. Recent technological advances resulted in a revolutionary breakthrough in the high-pressure crystallography. The structure solution and the full refinement are now possible at pressures over 100 GPa. A comprehensive understanding of the iron- and aluminum-bearing magnesium silicate perovskite (Pv) and post-perovskite (PPv, CaIrO3-type) crystal structures and their evolution under pressure and temperature is vital for evaluating seismic data of the Earth's lower mantle. We investigated materials with different compositions and iron oxidation states by means of single-crystal X-ray diffraction at pressures over 150 GPa and temperatures over 2500 K, and by Mössbauer spectroscopy. By structural studies of Pv at extreme conditions, we found (a) no spin state crossover in ferric iron occupying the bicapped trigonal prism ("A" crystallographic site), and (b) no crystal-chemically significant amount of ferric iron in the octahedral "B-site at any conditions of our experiments. We synthesized single crystals of PPv, refined their structure and distribution of iron between the structural sites. We demonstrated that incorporation of ferric iron and aluminum significantly increases the compressibility of magnesium silicate Pv and PPv. Based on experimental data we constrained the thermal equation of state for Pv and PPv with a variable content of iron (ferrous and ferric) and aluminum. We concluded that variation of Fe3+/ΣFe can lead to significant changes of Pv bulk sound velocity (over 1%) demonstrating that the oxidation state of iron is a critical parameter for interpretation of seismic tomography data.
Rationalising molecular crystal structures using Hirshfeld surfaces
Authors: Spackman Mark
Published: November 2015

Hirshfeld surface analysis [1] has very quickly become a routine tool for rationalising and visualising intermolecular interactions in crystals. The serendipitous discovery of an intriguing and novel way to identify the space `belonging' to a molecule in a crystal has led to the development of a suite of computational tools that facilitate a deeper understanding of how molecules pack in crystals and why it makes sense that a particular crystal packing occurs [2]. We have previously used the Hirshfeld surface as a vehicle for mapping inherent shape and curvature, surface-mediated distances between closest atoms, as well as quantum mechanical properties such as molecular orbital density, electron density and electrostatic potential. Combining visualisation tools like these with quantum mechanical wavefunctions – and hence properties derived from these wavefunctions – offers a powerful and unique opportunity to investigate intuitive concepts like `electrostatic complementarity' [3]. With this in mind we have been investigating ways to subdivide Hirshfeld surfaces into discrete patches that can be identified with specific pairs of molecules in close contact in crystals, and testing different expressions to quantify our ideas on electrostatic complementarity. Coupled with this appealing visual approach we also compute the electrostatic energy of interaction between the respective molecular wavefunctions. This combination of approaches within an easy to use software package will be powerful enough to not only routinely explore and visualise the patterns of interaction exhibited by molecules in crystals, but also provide meaningful energies of interaction between relevant pairs of molecules. In this way we can readily attach some real significance – energetics – to what are more usually classified as close contacts of various kinds.
Defect mastering - one of the topic challenges for crystal growth
Authors: Rudolph Peter
Published: November 2015

The quality of single crystals, epitaxial layers and devices made there from are very sensitively influenced by structural and atomistic deficiencies generated during the crystal growth. Crystalline imperfections comprise point defects, dislocations, grain boundaries, second-phase particles. Over more than a half-century of the development of crystal growth, most of the important defect-forming mechanisms have become well understood [1-2]. As a result, the present state of technology makes it possible to produce crystals of remarkably high quality. However, that is not to say that all problems are already solved. For instance, in comparison with silicon the point defect dynamics in semiconductor and oxide compounds is not nearly as well understood. The density of equivalent defect types and antisites in each sub-lattice is determined by deviation from stoichiometry. Their charge state depends on the Fermi level position leading via interaction with dopants to certain compensation level and complex formation. One measure proves to be the in situ control of stoichiometry. Due to high-temperature dislocation dynamics heterogeneous dislocation substructures are formed. Both, acting thermo-mechanical stress and given point defect situation force the dislocation to glide and climb. In the course of enthalpy minimization the long-range character of dislocation interaction produces agglomerates and patterns with polygonized cell walls, i.e. small angle grain boundaries [3]. Thanks to the rules of correspondence of Taylor and Kuhlmann-Wilsdorf one is able to estimate the interaction between shear stress, dislocation density and cell diameter (Fig.). In epitaxy the Nye tensor, describing dislocation distribution inhomogeneity, affects the layer stress considerably. The growth under minimum stress, solution hardening and in situ stoichiometry control are effective counteracting methods. One of the most serious consequences during cooling down of as-grown crystals is the point defect condensation in precipitates and micro-voids decorating dislocation patterns or inducing high mechanical misfit stress that generates dislocation loops. It proves to be favourable to anneal the crystal a few degrees below the melting point in order to dissolve the particles and re-diffuse their into the crystal matrix.
Insight from energy surfaces: structure prediction by lattice energy exploration
Authors: Day Graeme
Published: November 2015

A long-standing challenge for the application of computational chemistry in the field of crystallography is the prediction of crystal packing, given no more than the chemical bonding of the molecules being crystallised. Recent years have seen significant progress towards reliable crystal structure prediction methods, even for traditionally challenging systems involving flexible molecules and multi-component solids [1]. These methods are based on global searches of the lattice energy surface: a search is performed to locate all possible packing arrangements, and these structures are ranked by their calculated energy [2]. One aim of this lecture is to provide an overview of advances in methods for crystal structure prediction, focussing on molecular organic crystals, and highlighting strategies that are being explored to extend the reach of these methods to more complex systems. A second aim is to discuss the range applications of crystal structure prediction calculations, which have traditionally included solid form screening, particularly of pharmaceutically active molecules, and structure determination. As energy models become more reliable at correctly ranking the stability order of putative structures, and the timescale required for structure searching decreases, crystal structure prediction has the potential for the discovery of novel molecular materials with targeted properties. Prospects for computer-guided discovery of materials will be discussed.
Local atomic structure determination using focused electron beams
Authors: Etheridge Joanne
Published: November 2015

This talk will give an overview of methods for solving the atomic structure of nanostructured materials using focused electron beams. It will illustrate these methods with a range of applications, such as the determination of the atomic structure and stability of nanoparticle facets [1]; the local atomic structure of "chessboard' nanostructures in lithium-based titanate perovskites; and the measurement of local polarity, dopant concentration and atomic-scale morphology in semiconducting nanowire quantum wells. These methods take advantage of the fact that electron wavefields can be brought to a focal point smaller than an Ångström in diameter, enabling small volumes of matter to be probed and characterized. The wealth of information contained in the resulting diffraction patterns can be interrogated selectively to isolate and `image' specific structural information. Several methods using small focused electron beams will be described in this talk, including; (i) An approach for the determination of centrosymmetric structures from the direct observation of structure factor phases by inspection of features in convergent beam electron diffraction patterns [2]. The method can achieve high resolution from just a few phase observations and no intensity measurements or iterative refinements are required; (ii) Methods for the quantitative interpretation of the intensity in atomic resolution imaging and diffraction data for the measurement of local atomic and electronic structure; (iii) Pseudo-confocal scanning transmission electron microscopy methods for obtaining depth and chemical information which record the scattered intensity in a plane conjugate to the specimen (as opposed to the diffraction plane) [3].
New opportunities in structural biology with XFEL: from sources to structures
Authors: Wakatsuki Soichi
Published: November 2015

X-ray free electron lasers (XFEL) have shown the promise of providing new opportunities in structural biology research with their extremely high peak brilliance and short pulses. It is reaching the stage where biologically important questions can be tackled using XFEL based on the "diffract-before-destroy" concept. The first part of this presentation will focus on macromolecular crystallography using XFEL with results obtained at LCLS so far and future scope. R&D efforts being pursued at SLAC/LCLS include new beam modes, (two-color beam for de novo phasing, wider bandwidth for SAXS/WAXS and spectroscopy), beam multiplexing, a dedicated new station for in-air data collection, next generation detectors, data analysis incorporating pulse-by-pulse spectrometer measurements and post refinement. These projects are being pursued in collaboration with many groups locally and globally with a goal to provide integrated facilities for cutting edge structural biology research. For example, two-color self-seeded XFEL mode is being developed for simultaneous recording of diffraction data at two energies in order to optimize the dispersive difference between the two wavelengths for phasing. Another area of collaborative effort is a development of dedicated station for in-air data collection with a variety of sample delivery schemes. The second part will discuss a possible roadmap towards atomic resolution single particle imaging using XFEL. Here, key questions are ·Can XFEL single particle 3D structural analysis at atomic resolution be done? ·What is the pulse characteristics required? ·Can we overcome the radiation damage at soft X-ray regime? ·What is the highest resolution attainable in comparison with cryoEM? A workshop at LCLS is being organized to discuss these questions in 4 areas: radiation damage, image reconstruction algorithm, beam modes and instrumentation, sample delivery and heterogeneity. The outcome of the workshop and follow-up discussions will be presented.
Mathematical Crystallography in the 21st century
Authors: Senechal Marjorie
Published: November 2015

The solution of simple crystal structures in 1914 sent crystallographers to the library stacks to dig out, dust off, and learn to use the lattices and space groups that mathematicians had discovered in the century before. In 2014 space group assignment is a job for computers, but mathematical crystallography is anything but routine. New materials stretch the boundaries of "pattern," simulations stretch the boundaries of "possible," and mathematicians study structures on all scales, from nano to n-dimensional. In this talk I will outline challenges and new directions posed by 21st century crystallography.
Neutrons and supercomputing for Complex Biological Systems
Authors: Langan Paul
Published: November 2015

Frontier challenges in biological research increasingly require gaining a predictive understanding of complex dynamic and flexible multi-component systems. Gaining that understanding can come from combining several experimental approaches to inform multi-scale computer models and simulations. Complementary experimental approaches used include electron microscopy, mass spectrometry, X-ray scattering, and NMR, but outstanding challenges remain. Neutron scattering has great potential to address the remaining challenges by providing elusive information that cannot be obtained otherwise. Researchers are now gaining access to new instrumentation on intense neutron beam lines at the Spallation Neutron Source (SNS) and the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL). An unprecedented opportunity exists that we are exploiting by developing and broadening the use of neutrons in biological research by leveraging deuterium labeling and high performance computing. In order to develop this innovative integrated approach, and to take full advantage of the increase in availability and capability of neutron beam lines, further technological advances are required. In this talk I will present an overview of neutron facilities at ORNL, and give examples of their growing application in biological research. I will then discuss how the future challenges in biology are driving further technological developments that will lead to new understanding in the emerging areas of dynamic functional assemblies, disorder and flexibility, biological membranes and associated complexes, and biomolecular function and ligand binding. Neutrons can provide unique information that will transform these areas of research, opening up new lines of biological inquiry.
A decade of multiferroic research: new concepts and materials
Authors: Chapon Laurent
Published: November 2015

In the last 10 years, the surge of interest for multiferroics has allowed to identify several new classes of materials in which electric and magnetic degrees of freedom are highly coupled. In particular, in the so-called type II multiferroics, the onset of long range magnetic order induces ferroelectric polarization and the magnetic domains can be controlled by an electric field or conversely the direction of the polarization can be flopped by a magnetic field. I will review the most recent discovery in the field, and show how neutron and X-ray magnetic scattering provide a very detailed understanding of the magnetoelectric coupling mechanism.
Precession Electron Diffraction
Authors: Midgley Paul
Published: November 2015

The strong Coulombic interaction between a high energy electron and a thin crystal film gives rise to electron diffraction patterns encoded with information that is remarkably sensitive to the crystal potential. That exquisite sensitivity can be advantageous, for example in the determination of local symmetry and bonding, but can also be problematic in that in general the dynamical scattering inherent in electron diffraction prohibits the use of conventional crystallographic methods to recover structure factor phase information and solve unknown structures. One way to reduce this problem is to use precession electron diffraction (PED), introduced 20 years ago [1] as the electron analogue of Buerger's X-ray technique, in which the electron beam is first rocked in a hollow cone above the sample and then de-rocked below, the net effect of which is equivalent to precessing the sample about a stationary electron beam. PED is now used almost routinely as a starting point to solve crystal structures that cannot be solved for a variety of reasons using x-ray or neutron methods. In this keynote lecture we explore why the PED technique has been successful for structure determination, focussing on the PED geometry, the variation of intensities with precession angle and specimen thickness, and how this `mimics' kinematic behaviour, and the use of unconventional structure solution and refinement approaches [2]. New acquisition geometries will be discussed that rely on tilt series of PED patterns to yield a more complete 3D data set. The lecture will focus on how PED has been used also as a method for nanoscale orientation mapping [3], providing more information than conventional electron diffraction and a robust method with which to determine local crystallographic orientation. By scanning the beam, accurate orientation images can be derived from series of PED patterns and, by combining with tomographic methods, sub-volume orientation information is also available.
Synchrotron radiation macromolecular crystallography: our science and spin offs
Authors: Helliwell John
Published: November 2015

I will give an overview of synchrotron radiation (SR) in macromolecular crystallography (MX) instrumentation, methods and applications from the early days to the present, including the evolution of SR sources and on to the `ultimate storage ring'. The build of dedicated beamlines for resonant anomalous scattering, large unit cells, ever smaller crystals and studies up to ultra-high resolution are core benefits. Results include a high output of PDB depositions, the successful use of microcrystals, pushing the frontiers of using high and low photon energies and time-resolved structural studies at even sub-nanosecond resolutions. These intensively physics based developments will be complemented by biological and chemical crystallography research results, encompassing catalysis and marine coloration, as well as the public understanding of our science and its impacts. Spin off benefits include services to the pharmaceutical industry and helping develop chemical crystallography uses of SR. The development of the Laue method with SR has led to pioneering spin off developments in neutron MX, including transfer of the well validated Daresbury Laue software to various neutron facilities worldwide. Neutron MX is gathering pace as new instrumentation and dedicated sample preparation facilities are in place at reactor and spallation neutron sources; smaller samples and much larger molecular weight protein complexes are now feasible for investigation so as to establish their protonation states and bound water structure. With the X-ray lasers, closely linked to the SR developments, we anticipate the use of ever smaller samples such as nanocrystals, nanoclusters and single molecules, as well as opening up femtosecond time-resolved diffraction structural studies. At the SR sources, a very high throughput assessment for the best crystal samples and tackling sub-micron crystals will become widespread.
The First X-ray Powder Diffraction Measurements on Mars
Authors: Bish David
Published: November 2015

The CheMin instrument on the Curiosity rover measures XRD and XRF data using Co radiation in transmission geometry. It has analyzed <150 μm portions of eolian soil (Rocknest) and two drill-hole powders (John Klein and Cumberland) from a mudstone [1, 2, Figure 1]. XRD data for Rocknest soil revealed plagioclase, forsteritic olivine, augite, and pigeonite. John Klein and Cumberland are similar, with much less Fe-forsterite and more magnetite than Rocknest. Data were analyzed via Rietveld methods (Topas), and profiles were modeled using beryl-quartz data measured on Mars. CheMin's broad profiles limited analysis of minor phases (<3 wt. %), although the presence of minor phases was evaluated individually for every sample by including each in the Rietveld model and evaluating their effect on the fit. We found no evidence for any perchlorate, carbonate, or sulfate mineral (apart from anhydrite, and bassanite in the mudstones). No phyllosilicate was detected in the soil, but mudstone samples contained two different phyllosilicates, likely trioctahedral smectites. The John Klein XRD pattern had a broad ~10Å peak, whereas Cumberland showed broad peaks at ~13.2Å and ~10Å. The background in all XRD patterns suggested the presence of amorphous/poorly ordered components, which were analyzed using FULLPAT, giving ~27% amorphous content in Rocknest and ~20% in the mudstones. This mineralogy is very similar to that found in soils on the flanks of Mauna Kea volcano, Hawaii. Mineralogy differences between the Rocknest material and the mudstones may be explained by alteration of Fe-forsterite to smectite + magnetite. Combining these results with compositional estimates from unit-cell parameters and bulk chemistry will allow determinations of individual phase compositions, including that of the amorphous component(s). The exact nature of the amorphous component is unclear, but other data show that it is hydrous.
From the Crystal to the Rose: The Route to Biomimetic Self-assembled Nanostructured Materials
Authors: García-Ruiz Juan Manuel
Published: November 2015

Life was able to create (bio)chemical pathways to mineral structures of great complexity, breaking the symmetry of single crystals into complex textures exhibiting morphologies with continuous curvature forbidden in crystal symmetry. Materials with non-crystalline morphologies can be made out of crystalline phases by filling volumes or coating surfaces with curved shapes. However, what wonders and challenges engineers and material scientists is the ability of life to create such a complexity by self-assembly. The formation of architectures such as shells and other exoskeletons of living organisms is governed by organic molecules or matrices, which modify crystallization in a deliberate manner. Their influence provokes the breaking of the single crystal character of the mineral precipitation and often leads to sinuous shapes, which have been thought to be a sign of life, and distinguish these minerals from their inanimate, mostly euhedral counterparts. In this lecture I will review a laboratory inorganic route to these biological structures. It has been discovered that silica -an ubiquitous mineral in the geological record, particularly in the early years of the planet- has a strong influence on the precipitation of carbonate and hydroxides. Under alkaline conditions, the chemical coupling of silica with CO3= and OH- creates abiotic, purely inorganic, self-assembled structures made of millions of nanocrystals building textures of high complexity and showing morphologies with continuous non-crystalographic curvature. The process of self-assembly, driven by a pH-based coupling of the chemistry of carbonate and silicate, is explored for applications in materials science. I will also discuss the geochemical plausibility of these self-organized mineral processes in terms of their implication in the origin of life and primitive life detection. Figure 1: Chemically induced cooperative phenomena break the restricted point symmetry of single crystals into self-assembled nanocrystalline structures with complex shapes of continuous curvature.
Exploring consumer preferences for hedonic and utilitarian food attributes
Authors: Maehle Natalia , Iversen Nina , Hem Leif , Otnes Cele
Published: November 2015

Purpose

– The purpose of this paper is to identify the relative importance of four main attributes of food products for consumer’s choice. These are price, taste, environmental friendliness and healthfulness, tested across hedonic and utilitarian food products (milk and ice-cream). The weighting of attributes involved in food choices is a complex phenomenon, as consumers must consider contradictory requirements when making their choices. Consumers’ decision-making processes might also be influenced by food category. Some food products are mostly consumed for pleasure, whereas others are consumed because of their nutritional value.

Design/methodology/approach

– The study employs a choice-based conjoint technique, which addresses how consumers make trade-offs across a set of product attributes.

Findings

– The results indicate that price and taste attributes are rated as the most important for both hedonic and utilitarian food products. However, when the authors group consumers according to their product preferences, the relative importance of product attributes changes. Specifically, the importance of environmental friendliness and healthfulness is much higher among the health-conscious and environmentally conscious segments than for other segments.

Originality/value

– To the knowledge, this is the first study comparing the importance of this combination of product attributes (price, taste, calorie content and eco-label) across hedonic and utilitarian foods in a choice-based conjoint setting. Moreover, a new way of grouping consumers according to their ethical-value profiles enables the authors to create a psychographic description of these segments, and to relate it to their food attribute preferences.