bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase Evolution of Al/Cu/Co Thin Films into Decagonal Quasicrystalline Phases
Authors: Eriksson Fredrik , Olsson Simon , Garbrecht Magnus , Birch Jens , Hultman Lars
Published: November 2015

Quasicrystals have drawn increased scientific attention during the past decade not only for the purpose of fundamental research, but also due to their possible applications as bulk materials or thin films [1]. In particular, decagonal (d) quasicrystals could be very attractive because of their anisotropic structure being quasiperiodic in two dimensions and periodic in the third. Recently it has been shown that icosahedral quasicrystalline Al-Cu-Fe and approximant Al-Si-Cu-Fe thin films can be prepared by annealing a multilayer thin film on a sapphire or Si substrate, respectively [2]. In this work, multilayered Al/Cu/Co thin films have been deposited by magnetron sputtering onto Al2O3 (0001) and Si (001) substrates. The multilayers were produced with a multilayer period of 100 nm, repeated 3 times to a total thickness of 300 nm. The Al:Cu:Co layer thickness ratios were adjusted to obtain films with global compositions around the ideal decagonal quasicrystalline phase d-Al65Cu17.5Co17.5. The phase evolution during annealing, and the concurrent changes in film microstructure and crystal quality was investigated. The decagonal d-Al-Cu-Co and d-Al-Cu-Co-Si phases were both found by X-ray diffraction, electron diffraction, and high-resolution (scanning) electron microscopy to form at 5000C on Al2O3 and Si, respectively, and at 6000C these were the only phases present. Figure 1 shows the HRTEM micrograph of the Al-Cu-Co-Si phase after annealing to 7000C. At increasing temperatures, the quasicrystal grains grew larger in size, up to 500 nm, and the Al-Cu-Co obtained a preferred orientation with the 10-fold periodic axis aligned with the Al2O3 substrate normal. The d-Al-Cu-Co phase persisted to more than 8500C, with a complete 00001-texturing, while the d-Al-Cu-Co-Si phase was replaced by other crystalline phases at 8000C. The d-Al-Cu-Co-Si phase was also observed to grow into the Si substrate by a solid-state diffusion reaction.
Templated quasicrystalline ordering of single elements and molecules
Authors: Sharma H. R. , Smerdon J. A. , Nozawa K. , Young K. M. , Yadav T. P. , Dhanak V. , Ishii Y. , Shimoda M. , Tsai A. P. , McGrath R.
Published: November 2015

We have used quasicrystals as templates for the exploration of new epitaxial phenomena. Several interesting results have been observed in the growth on surfaces of the common Al-based quasicrystals [1]. These include pseudomorphic monolayers, quasiperiodically modulated multilayer structures, and fivefold-twinned islands with magic heights influenced by quantum size effects [1]. Here we present our recent works on the growth of various elements and molecules on a new substrate, icosahedral (i) Ag-In-Yb quasicrystal, which have resulted in various epitaxial phenomena not observed previously. The growth of Pb on the five-fold surface of i-Ag-In-Yb yields a film which possesses quasicrystalline ordering in three-dimension [2]. Using scanning tunneling microscopy (STM) and DFT calculations of adsorption energies, we find that lead atoms occupy the positions of atoms in the rhombic triacontahedral (RTH) cluster, the building block of the substrate, and thus grow in layers with different heights and adsorption energies. The adlayer–adlayer interaction is crucial for stabilizing the epitaxial quasicrystalline structure. We will also present the first example of quasicrystalline molecular layers. Pentacene adsorbs at tenfold-symmetric sites of Yb atoms around surface-bisected RTH clusters, yielding quasicrystalline order [3]. Similarly, C-60 growth on the five-fold surface of i-Al-Cu-Fe at elevated temperature produces quasicrystalline layer, where the growth is mediated by Fe atoms on the substrate surface [3]. The finding of quasicrystalline thin films of single elements and molecules opens an avenue for further investigation of the impact of the aperiodic atomic order over periodic order on the physical and chemical properties of materials.
Structural phase transitions and conducting properties in Bimetallic sulfates
Authors: Sharma Vaishali , Swain Diptikanta , Narayana Chandrabhas , Guru Row Tayur
Published: November 2015

Bimetallic sulfate minerals, hydrated as well as anhydrous are important multifunctional materials which exhibit interesting properties like fast-ion conduction, ferroelectricity and magnetism with variation in temperature [1,2,3]. These properties are generally entwined with structural phase transitions and show structural frameworks made of interconnection of octahedra and tetrahedra [1]. Bimetallic sulfates, indeed are intercalation compounds of alkali ions generated by these frameworks and they possess high ionic conductivity [1]. In the present study, anhydrous and hydrous compounds of Na6M(SO4)4, (M=Mn, Ni, Co) were synthesized to understand the structural phase transitions and its relation to fast-ion conducting properties. Na6Mn(SO4)4, is monoclinic, space group P21/c with Z=2 and is isostructural to its Co and Ni analogues and shows high ionic conductivity and structural phase transition > 4500C. Na6Co(SO4).2H2O, Na6Ni(SO4).2H2O are isostructural with triclinic system having space group P-1 with Z =1. In addition, structural features and correlation with ionic conductivity in Na6Co(SO4).2H2O, Na6Ni(SO4).2H2O and Na6Mn(SO4) will be outlined. These studies open up the utility of hydrated bimetallic sulfates as possible precursor for the design of functional materials.
Metal oxide materials for high temperature CO2sorption studies
Authors: Pavan Adriano , Blanchard Peter , Liu Samuel , Ling Chris
Published: November 2015

In recent years, a number of novel ceramic oxide materials have emerged that are capable of absorbing CO2 at high temperatures (>500C) while remaining stable over a large number of cycles and a wide range of temperatures [1]. The most promising are been considered for carbon capture applications – specifically, for use in combustion chambers and the smoke stacks of power plants where combustion gases which contain primarily a mixture of CO2 and N2 at high temperature. Compared to other CO2 sequestration technologies, these ceramics have some advantages (eg. chemisorption at high temperatures) and disadvantages (eg. limited kinetics over time) [3]. Examples of oxides already known to show significant CO2 absorption include Li5AlO4, Li6Zr2O7, Na2ZrO3 and Ba4Sb2O9. The phase formations and structural evolution of these metal oxides have been studied under environmental conditions mimicing those found in combustion chambers and power plants, over the temperature range 873–1173 K. CO2 absorption by these materials is believed to proceed through a layering effect of the sorbent material, explained through a core-shell model (see figure). Each phase is represented as a layer covering a particle, with the outermost layer exposed and allowed to react with the environment. Detailed studies into the mechanism of CO2 absorption and the material layers will shed more information that can be used to fine tune the materials to increase their CO2 absorption capacity. Previous work has focused on the identification of phases ex situ and studies of their practical absorption capacity and kinetics. The new work we will present here uses a combination of a x-ray spectroscopy, x-ray and neutron diffraction, to understand both how the sorption process works and how the structural evolution of the phases affects the CO2 sorption of the materials over time in-situ.
Low temperature phase transition and structure of CsMgPO4
Authors: Orlova Maria , Perfler Lukas , Michailov Dmitriy , Orlova Albina , Khainakov Sergei , García-Granda Santiago , Langes Christoph , Tappert Ralf , Kahlenberg Volker
Published: November 2015

CsMgPO4 doped in radioisotopes is a promising compound for usage as a radioactive medical source. However, a low temperature phase transition at the temperatures close to ambient conditions (-370C) was observed. Information about structural changes is important in order to understand whether it can cause any problem for medical use of this compound. Structural changes have been investigated in detail using synchrotron powder diffraction methods, Raman spectroscopy and DFT calculations. The structure undergoes transformation from orthorhombic modification, sp. gr. Pnma (RT phase) to monoclinic modification, sp.gr P21/n (LT phase). New LT modification adopts similar to RT but slightly distorted unit cell: a=9.58199(2)Å, b=8.95501(1) Å, c=5.50344(2)Å, β=90.68583(1)0, V=472.198(3) Å3. The framework is made up of alternating magnesia and phosphate tetrahedra sharing vertices with caesium counter cations located in the channels formed. Upon the transformation a combined rotation of PO4 and MgO4 tetrahedral takes place. A comparison with other phase transition in ABW-type framework class compounds is given.
Calcium phosphate phase transition in the presence of Aminosilane
Authors: Mostaghaci Babak , Loretz Brigitta , Haberkorn Robert , Kickelbick Guido , Lehr Claus-Michael
Published: November 2015

Calcium phosphate has been the point of interest for in vitro gene delivery for many years because of its biocompatibility and straight forward application. However, there are some limitations regarding in vivo administration of these particles mostly because of vast agglomeration of the particles and lack of strong bond between the particles and pDNA. We introduced a simple single step method to functionalize calcium phosphate nanoparticles with Aminosilanes having a different number of amine groups. The nanoparticles were characterized chemically and structurally and their toxicity and interaction with pDNA were studied as well. Results revealed that different crystalline phase of calcium phosphate nanoparticles (Brushite and Hydroxyapatite) with a size below 150 nm were prepared, depending on conditions of synthesis and phase, each with a narrow size distribution. The aminosilane agents caused oriented nucleation and growth of crystallites and can decrease the pH for producing hydroxyapatite phase. The phenomenon could be revealed with the presence of anisotropy in the structure of synthesized hydroxyapatite. The number of amine groups in the Aminosilane agent could change the phase transition pH. Brushite particles revealed to have stronger interaction with pDNA mostly because of their higher positive surface charge. Both particles showed blood compatibility and negligible toxicity. Transfection experiment revealed the capability of both brushite and hydroxyapatite particles to transfect A549 and HEK293 cells. The new modified nanoparticles can be stored in a dried state and re-dispersed easily at the time of administration. Moreover, the transfection efficiency is higher in comparison with conventional calcium phosphate. This study showed the impact of presence and type of the modifying agent on the crystal structure and the amount of surface functionalization of nanoparticles, which in consequence influenced their interaction with cells.
Diagenesis and kerogen release in oil- and gas-bearing shales
Authors: Littrell Kenneth , Anovitz Lawrence , Rother Gernot , Cole David , McPherson Greggory , DeBeer-Schmitt Lisa
Published: November 2015

The microstructure of pore space in sedimentary rocks and its evolution during reaction with pore- or fracture-contained fluids is a critically important factor controlling fluid flow properties in geological formations, including the migration and retention of water, gases and hydrocarbons. The size, distribution and connectivity of these confined geometries (pores, fractures, grain boundaries), collectively dictate how fluids of various chemistries migrate into and through these micro- and nano-environments, wet, and ultimately react with the solid surfaces. In order to interpret the time-temperature-pressure-fluid flow history of any geological system, the physical and chemical "fingerprints" of this evolution preserved in the rock must be fully explored over widely different length scales from the nanoscale to the macroscale. We are experimentally investigating these reaction-controlled changes in rock microstructure by conducting in-situ heating experiments on samples of the Garfield oil shale. Oil shale, an organic-rich fine-grained sedimentary rock, contains significant amounts of kerogen (a solid mixture of organic chemical compounds) from which liquid hydrocarbons can be extracted. Pyrolysis (heating shale in the absence of oxygen) converts the kerogen in the oil shale to shale oil (synthetic crude oil) and oil shale gas and a solid residue. Through SANS, we clearly observe these kerogen and oxidation release at lower temperatures followed by pore structure reordering and finally enlargement at higher temperatures. These results are compared with preliminary results tracking the natural diagenesis of the commercially-important Eagle Ford shale formations across the oil/gas boundary.
Evaluation of structural phase transition by pyroelectric measurements
Authors: Jachalke Sven , Mehner Erik , Stöcker Hartmut , Leisegang Tilmann , Meyer Dirk
Published: November 2015

In non-centrosymmetric crystalline matter, marked by the pyroelectric effect, a change in temperature alters the materials spontaneous polarization, which further changes the charge density on the material's surface. This results in a current flow trough an external circuit, which differs drastically at the boundary between two crystallographic phases. Therefore, pyroelectric materials offer a great potential of low-temperature waste heat recovery by utilizing e.g. the Olsen-Cylce to convert residual heat into electric energy. A previous characterization is necessary to determine the operating conditions of the active material. This work presents a method to evaluate temperature depended pyroelectric properties, especially the pyroelectric coefficient p and the phase transition temperture TC, with the help of a computer controlled thermal/electrical stimulation and a simultaneously recording of the electrical response of the material. Here, the analysis with the Sharp-Garn-method [1] separates the pyroelectric from eventually disturbing non-pyroelectric signal, enabling the characterization of p and TC over a broad spectrum of materials, ranging from inorganic single crystals and ceramics to organic polymers.
Characterization of Pressure-induced Phase Transition on [Co(bpy)3](NO3)2·3H2O
Authors: Lee Ya-Wen , Chuang Yu-Chun , Lee Jyh-Fu , Lee Chi-Rung , Lin Chih-Ming , Hsu I-Jui
Published: November 2015

The pressure-induced phase transition study of high-spin (HS) compound, [Co(bpy)3](NO3)2·3H2O (bpy = 2,2'-bipyridine), is characterized by powder x-ray diffraction (XRD), x-ray absorption spectroscopy (XAS), Raman spectroscopy, and theoretical calculations. The results indicate that the HS ground state t2g5eg2 on Co(II) is gradually transformed to low-spin (LS) state with configuration t2g6eg1 . This phase transition behavior is similar to the thermal-induced spin crossover phenomenon once it is incorporated into certain framework. In this study, we put the compound into diamond anvil cell and applied physical pressure to replace the framework effect. To analyze the x-ray absorption near edge structure (XANES) and Raman spectroscopy, the finite difference method for near-edge structure (FDMNES) and density functional theory (DFT) calculations are applied to illustrate the experimental spectroscopies, respectively. In XANES results, an intersection point around 7756.33 eV beyond 1.73 GPa is assigned as the critical point between HS and LS state. The extended x-ray absorption fine structure (EXAFS) analysis indicates that the averaged Co-N bond lengths is 2.127(7) Å at HS state and decreased to 1.950(4) Å at LS state. Based on XRD analysis, the external pressure reduces the hexagonal cell constants from a = 13.77(3) Å and c = 21.71(3) Å to a = 13.37(5) Å and c = 21.11(1) Å. According to those experimental results, the mechanism of such pressure-induce spin transition can be interpreted as the enhancement of intermolecular interaction by increasing the external pressure.
Neutron diffraction on functional materials under electric field or mech. load
Authors: Hoelzel Markus , Hinterstein Manuel , Kadletz Peter , Schmahl Wolfgang
Published: November 2015

In this contribution neutron diffraction studies on functional materials under special environmenal conditions will be presented. In particular, studies of ferroelectric ceramics under high electric fields as well as shape memory alloys under mechanical load will be highlighted. The investigations were carried out at the high-resolution neutron powder diffractometer SPODI (FRM II / Garching n. Munich) which offers special sample environmenal tools for electric fields, mechanical load etc. In-situ studies on ferroelectrics under the influence of high electric fields enable to establish correlations between the macroscopic poling behaviour and corresponding structural changes. The investigations were carried out on technologically applied lead zirconate titanate based samples and on a bismuth sodium titanate based system. A self-designed device allows the investigation of large bulk samples under different orientations of the electric field. This method allows to analyze the poling mechanisms in technical ferroelectrics, such as piezoelectric effect, domain reorientation and phase transformations. In the system Bi0.5Na0.5TiO3 - BaTiO3 – K0.5Na0.5NbO3 the large recoverable field-induced strain could be attributed to a reversible field-induced phase transition from an almost non-polar, pseudocubic tetragonal phase to a distorted, ferroelectric active phase [1]. Polycristalline monoclinic nickel-titanium shape memory alloys have been investigated under mechanical load to analyze their stress-strain behaviour and to derive the elastic constants. A novel tensile rig allows to orient the load axis in a Eulerian cradle like manner. The elastic constants tensor could be calculated based on a series of diffraction patterns under different sample orientations in the initial state and under 0.6 % strain. Furthermore the contributions of elastic deformation (lattice dilatation) and inelastic deformation (orentation of twins) to the total strain could be separated.
Fluorides containing lanthanides and yttrium at extreme conditions
Authors: Grzechnik Andrzej , Friese Karen
Published: November 2015

We are interested in crystal structures and stabilities of fluoride materials containing lanthanides and yttrium that are related to the CaF2 structure. These compounds are laser hosts and luminescent materials, oxygen sensors as well as components of solar cells. They exhibit various schemes of (dis)ordering of cations and anions in fluorite superstructures and anion-excess fluorites. In the last few years, we have performed a series of studies on the bulk AMF4 and MF3 materials (A = Li, Na, K; M = Y, lanthanide) at different pressure-temperature conditions. Among them, ordered LiYF4 is a commercial host for solid state lasers, while partially ordered NaYF4 doped with lanthanides is the most efficient material for green and blue up-conversion known to date. In the system KF–YF3, we have studied not only KYF4 [1] but also KY3F10, which is an anion-excess 2×2×2 superstructure of fluorite at atmospheric conditions. At high temperatures and high pressures, it converts to another fluorite superstructure with disordered fluorine atoms. The pressure-induced LaF3 post-tysonite structure is another example of the anion-excess fluorite [2]. Our work on the fluorite-related materials at extreme conditions provides information on their structural instabilities that could further be used to better understand and control their materials properties. For instance, we demonstrated that the NaMF4 up-converters are unstable and that the ordering of the cations and vacancies in their structure is a slow process [3]. Consequently, the order–disorder transformations have a profound influence over the luminescent properties of these materials when doped.
Thermal expansion of Carbonate-Nosean: a phase-transition kinetics model
Authors: Gesing Thorsten , Murshed M. , Robben Lars
Published: November 2015

The description of a Landau phase-transition considers group-subgroup relations with respect to the initial phase at thermodynamic equilibrium. Accordingly, the Gibbs free energy is modified in terms of an order parameter Q [1]. Data collection on a particular phase at equilibrium is challenging in case of associated kinetic effects. Thus describing a phase-transition using the Landau theory leads quite often to a marked discrepancy between the observed and calculated data close to Tc. Evaluating an accurate order parameter consequently must be a hurdle. In some cases the order parameter is proportional to the unit-cell volume of the phase. Similar effect could be seen while evaluating the lattice volume of a phase using Debye-Einstein-Anharmonicity model [2] where the internal energy of a crystalline lattice volume is considered to be sum of the Einstein harmonic, Debye quasi-harmonic and anharmonic vibrational potentials. The DEA-model gives possibility to compare the experimental thermal expansion coefficient (TEC) with that of the theoretical one. For example, in dehydrated carbonate-nosean [3] the kinetic effect close to the P23-P23 phase-transition could be seen in terms of the decrease of the TEC over several data points around 800 K (Figure). In this case, a pure Landau transition would have sharply dropped the TEC leaving no intermediate values. These deviations in the experimental data could be theoretically modeled by overlapping the TEC's of the low-temperature (TECLT) and the high-temperature (TECHT) phase using a sigmoidal term fs(T) {0 < fs(T) < 1}: TECtotal(T) = fs(T)·TEClow(T) + (1- fs(T))·TEChigh(T). The slope of this sigmoidal function corresponds to the deviation of the model used for the volume calculation close to the phase-transition and therefore carries information about the reaction kinetics. The same could be calculated for the dehydration process of the hydrated carbonate-nosean |Na8(CO3)(H2O)4|[AlSiO4]6around 400 K. Figure: Experimental temperature-dependent volume change of hydrated carbonate-nosean and respective DEA-model calculation results. The individual DEA-models as well as TEC changes including kinetic overlaps are given inserted.
First evidence of a phase transition in a high-pressure metal iodate.
Authors: Suffren Yan , Gautier-Luneau Isabelle , Darie Céline , Goujon Céline , Legendre Murielle , Leynaud Olivier
Published: November 2015

In the 1970s, a large number of metal iodates compounds were extensively investigated for their nonlinear optics (NLO) properties as well as for their ferroelectric, piezoelectric, and pyroelectric properties. Interest in these compounds resumed in the early 2000s. We have shown that metal iodates are particularly interesting for for quadratic NLO in mid IR, as they possess a large domain of transparency from the visible region to the beginning of the far IR region (12.5 μm), thus covering the three atmospheric transparency windows. The synthesis of metal iodates has so far been mainly investigated by solution chemistry, under hydrothermal conditions or by the flux method. The solid state synthesis of these compounds at high pressure has never been explored. To date, only the structural evolution of α-LiIO3 with pressure has been studied by X-ray powder diffraction [1]. It was shown that, at room temperature, α-LiIO3 is stable up to 75 GPa; only compression of the lattice parameters with pressure was observed. In this work, we present a new phase of silver iodate obtained at high pressure from α-AgIO3 and characterized by X-ray powder diffraction. The α-AgIO3 to β-AgIO3 transition was characterized by differential thermal analysis (DTA) at high pressure [2-3]. The thermal behaviors of α-AgIO3 and β-AgIO3 were studied by differential scanning calorimetry (DSC) at ambient pressure and in situ temperature-dependent X-ray powder diffraction. Structural studies of these two phases were carried out to understand the formation of β-AgIO3.
Structural modulations in multiferroic tetragonal tungsten bronze KxMnxFe1+xF3
Authors: Drathen Christina , Yusenko Kirill , Margadonna Serena
Published: November 2015

Multiferroic materials showing coupling of the different order parameters (ferroelectric, ferromagnetic, ferroelastic) are interesting not only from a fundamental perspective, but also from a technological point of view, e.g. for to the development of new storage technologies. However, the coexistence of (ferro)magnetism and ferroelectricity is considered a rare phenomenon. Whilst this may be true for perovskite oxides, where emptyd-shells favor the off-centering of ions but counteract magnetism, this intrinsic limitation can be avoided by moving to different structure types, and/or away from oxides. An example of non-perovskite, non-oxide multiferroic systems are the tetragonal tungsten bronze (TTB) fluorides KxM2+xM3+1+xF3(x= 0.4 – 0.6), which show coexistence of electric and magnetic ordering 1. Here we present a detailed structural study on a series of TTB fluorides, KxMnxFe1+xF3(x = 0.4 – 0.55). KMnFeF6has been previously described as tetragonalP42bcand orders ferrimagnetically belowT = 148 K 2. Additional satellite reflections were found in transmission electron microscopy experiments and attributed to ferroelastic domains arising from tilting ofMF6octahedra, but the reported bulk powder XRD measurements indicated only tetragonal symmetry 3. We used high-resolution powder diffraction techniques to reinvestigate the crystal structure as a function of temperature in comparison with DSC data. Our results reveal a structural distortion to orthorhombic symmetry (Ccc2) at room temperature, which diminished when moving to the end members of the series (x → 0.4 andx → 0.6). Although structurally subtle, this distortion may indicate a ferroelectric state, similar to KxFeF3, where ferroelectricity is observed only in the orthorhombic phase. On heating, an anomaly in thec-axis lattice parameter accompanies a phase transition to centrosymmetricP42/mbcaround 320 – 350 K, marking the transition from ferroelectric – paraelectric state.
Overlooked cation-ordered brownmillerite in Ba2(In1-xGax)2O5
Authors: Didier Christophe , Claridge John , Rosseinsky Matthew
Published: November 2015

As Goodenough showed 20 years ago, [1] Ba2In2O5 undergoes a transition from brownmillerite to cubic perovskite at higher temperatures, where it becomes a good oxygen ionic conductor. Past studies on doping gallium onto the indium sites [2] showed that higher Ga contents decrease the temperature required for the disordering to occur, in accordance with a higher structural disorder on the B site. In this work, we have showed that past studies on Ba2(In1-xGax)2O5 have overlooked a special ordering for the Ba2InGaO5 composition. Combined structure refinements of neutron and X ray powder diffraction show that this material adopts a brownmilleite structure below 1200°C with a layered ordering of In and Ga. This is one of a few examples of such an ordering in the brownmillerite structure only due to size difference between the B cations. This ordering further stabilizes the brownmillerite crystal structure compared to other compositions at smaller Ga contents. As could be expected, such stronger ordering is detrimental to ionic conductivity. At 1300°C, the material disorders into a cubic perovskite structure, which was already observed in past studies. However this polymorph has an unreported red colour, which was unexpected for a material with no incompletely filled orbitals. Incorporation of oxygen interstitial defects, on the basis of conductivity versus variable oxygen experiments and spectroscopic measurements, could be at the origin of this colouration much like in TiO2. [3] Unfortunately photocatalytic activity for water splitting could not be tested due to the strong instability of this material towards water.
X-Ray Diffraction Study of Oxygen-Conducting Compounds Ln2Mo2O9(Ln = La, Pr)
Authors: Antipin Alexander , Alekseeva Olga , Sorokina Natalya , Kuskova Alexandra , Presniakov Michail , Kharitonova Elena , Voronkova Valentina
Published: November 2015

Lanthanum molibdate La2Mo2O9(LM) and the compounds on its basis (LAMOX) attract much attention because of the high oxygen conductivity (6x10-2Sm/cm), which were found by Lacorre group. LM has the first-order phase transition at about 5800C and two phases: low-temperature monoclinic α-phase (P21) and high-temperature β-phase (P213) [1]. In the present work single crystals Ln2Mo2O9(Ln = La, Pr) were obtained by spontaneous flux crystallization in the Ln2O3–MoO3oxide systems. The LM and PM single crystals are studied by precision X-ray diffraction and high-resolution transmission microscopy. A cubic cell with a = 7.155(1) and 7.155(1) Å was chosen for two LM samples (LM_I and LM_II, respectively). More than 90% (LM_I) and 60% (LM_II) of the reflections measured were indexed in this cell. The unit cell parameter of the PM compound is slightly shorter: a = 7.087(1) and 7.089(1) Å for the PM_I and PM_II samples, respectively. More than 90% of the reflections measured were indexed for both PM crystals. It was found that the LM_II crystal consists of two cubic components grown together; a ≍ 7.155 Å for both components. The crystal structures for two LM and two PM samples are determined in space group P213. It is found that La and Pr atoms, as well as Mo1 and O1 atoms, are located in the vicinity of 3-fold axes rather than on the axes like in the high-temperature cubic phase. In both structures, the O2 and O3 positions are partially occupied. The coexistence of different configurations of the Mo coordination environment facilitates the oxygen ion migration in the structure. Based on the X-ray data, activation energies of oxygen atoms are calculated and migration paths of oxygen ions in the structures are analyzed. The conductivity of PM crystals is close to that of LM crystals. Oxygen atoms O2 and O3 make main contributions to ion conductivity of LM and PM. This study was supported in part by part by the Russian Foundation for Basic Research (project no. 14-02-00531).
Electric field induced pyroelectricity in strontium titanate
Authors: Mehner Erik , Hanzig Juliane , Jachalke Sven , Hanzig Florian , Zschornak Matthias , Stöcker Hartmut , Meyer Dirk
Published: November 2015

Pyroelectric materials have a broad spectrum for practical application. Apart from the established infrared sensor technology, recently the pyroelectric effect has been employed unconventionally in waste heat recovery, X-ray generation or water disinfection. This coupling phenomenon is the temperature dependence of a ferroelectric's spontaneous polarisation. A crystal structure that allows pyroelectricity cannot have an inversion centre, if it had a polar axis would not exist. Hence the well-known perovskite strontium titanate, crystallizing in the space group Pm-3m, is known to be dielectric. Nonetheless, under an external electric field of 1MV/m charged defects like oxygen vacancies redistribute in a strontium titanate single crystal, leading to a distortion of the unit cell and subsequently to the formation of a defect structure called the migration-induced field-stabilized polar (MFP) phase [1]. Raman scattering shows that the MFP phase of strontium titanate may exhibit broken centrosymmetry, suggesting the existence of a polar axis. Here, we investigate the pyroelectric properties of strontium titanate single crystals at room temperature during these electroformation cycles with a modified Sharp-Garn method [2]. Our frequency and field dependent measurements indicate the pyroelectricity of the MFP phase. Additionally the measurement method elucidates the kinetics of the oxygen vacancy migration as well as electric properties during electroformation. Inducing pyroelectricity in a centro-symmetric crystal structure opens the scope for a new class of pyroelectric materials.
Local Study on the Composition and Temperature Induced Structural Change of PZT
Authors: Zhang Nan , Yokota Hiroko , Glazer A. , Ye Zuo-Guang
Published: November 2015

The crystal structure and its relationship with the high piezoelectric performance of PbZr1-xTixO3 (PZT) have been studied for years, especially near the morphotropic phase boundary (MPB). Now the bridging monoclinic Cm phase in the MPB separating the not-group-subgroup-related R3c and P4mm has been widely accepted. However, in recent high-resolution powder diffraction experiments and Rietveld refinement analyses, the presence of the monoclinic Cm phase was found across the whole composition from the MPB to the rhombohedral region. Around the MPB, the structure seems to become more complicated, with a mixture of three phases[1]. It was also found that the local structure of PZT can be different from its average structure by examining the anisotropic displacement ellipsoids of both Pb and O: 1) the Pb atoms in the rhombohedral phase are displaced away from the threefold symmetry axes to create locally monoclinic symmetry that averages out to form an overall rhombohedral symmetry[2]; 2) at high temperature, the local effect of the low-temperature oxygen octahedra tilts remained even in the cubic phase[3]. In order to better study the local structures of PZT, we have carried out a series of high-resolution neutron diffraction experiments on both powder samples using Pair Distribution Function (PDF) analysis and single crystal samples using Diffuse Scattering (DS) analysis. The difference between the average and local structures is confirmed. The local distribution of the Pb displacements directions are plotted out for different compositions in PZT (x = 0.20, 0.30 and 0.40), which reveals on approaching MPB, the Pb atoms are tend to displace on one monoclinic mirror plane forming a macroscopic monoclinic phase. This is the first time that the local monoclinic short range order in Zr-rich PZT has been observed.
A Convergence of Beauty and Utility
Authors: Steeds John
Published: November 2015

The effective routine achievement of useful convergent beam electron diffraction (CBED) patterns was frustrated for many years until transmission electron microscopes (TEMs) were developed that overcame the practical difficulties. Because specimen thickness and orientation are two critical parameters in electron diffraction and are not under good control because of the difficulty of producing thin enough regions it was necessary to have TEMs capable of forming small focussed probes of less than 100nm diameter in local environments where the hydrocarbon level was sufficiently low to reduce carbon contamination to a reasonable level. Once these problems were overcome the importance of three-dimensional diffraction became apparent but to exploit this property it was necessary to develop TEMs with a large angular range in the diffraction plane. With appropriately designed instruments very beautiful CBED patterns could be obtained from crystalline samples and a variety of experimental techniques were exploited to extract meaningful information from them.
Atomistic Modeling of Crystal Nucleation and Growth
Authors: Parrinello Michele
Published: November 2015

Understanding crystal growth from solution is crucial to control the development of crystal morphologies. Since the interaction of crystals with their environment occurs through their surface, their shape controls a wide variety of properties. This is particularly important not only in nanotechnology, where shape-function relations play a key role, but also in medicine where, e.g., changing the morphology of particles allows for a better targeting of cancer cells. In this work we combine experiments, molecular simulations and theory to examine the morphology of urea crystals grown in different solutions. In order to get a rational representation of all the possible habits we introduce a Shape Diagram in which the habit dependence on the relative growth rates is displayed. A wide portion of the habit space can be experimentally explored by varying the composition of the mother solution. By doing so we obtain morphologies ranging from the paradigmatic needle-like habit obtained in water to regular tetrahedra obtained in acetonitrile/biuret mixtures. By combining advanced molecular simulation techniques and theory we can predict urea steady state crystal habits and their dependence on additive concentration and/or supersaturation, paving the way towards a rational control of the habit of crystals grown from solution. We present also some other example of nucleation processes which will lead to some rather surprising results even in the case of humble NaCl. Finally we discuss some recent advances that allow us to calculate nucleation rates.
A modulation wave approach to the long range order hidden in nominal 'disorder'
Authors: Withers Ray
Published: November 2015

While the definition of a crystal in terms of pure point diffraction/sharp Bragg reflections only is undoubtedly an excellent approximation for many crystalline materials, there exists a large and growing family of phases for which such a description is grossly inadequate: namely crystalline materials whose reciprocal spaces exhibit highly structured, continuous, diffuse intensity distributions which are essentially long range ordered in at least one or more dimensions (see e.g. Fig.1). To gain insight into both the local order, as well as the long range order, hidden in disordered materials of this type it is very helpful, if not essential, to use the language of modulated structures. An approach of this type automatically emphasizes the close relationship between the crystallography of disordered structures and aperiodic crystallography in general. In this contribution, the use of such an approach to understand the often highly structured shapes of such diffuse distributions, the characteristic extinction conditions frequently associated with them and the long range crystal chemical rules underlying their existence will be highlighted. Fig.1: <11-2> and <-110> zone axis electron diffraction patterns of (a) β-cristobalite and (b) SiO2-tridymite.
The future is bright-- structural biology at FELs
Authors: Schlichting Ilme
Published: November 2015

Protein crystallography using synchrotron radiation sources has had tremendous impact on biology, having yielded the structures of thousands of proteins and given detailed insight into their working mechanisms. However, the technique is limited by the requirement for macroscopic crystals, which can be difficult to obtain, as well as by the often severe radiation damage caused in diffraction experiments, in particular when using tiny crystals. To slow radiation damage, data collection is typically performed at cryogenic temperatures. With the advent of X-ray free-electron lasers (FELs) this situation appears remedied. Theoretical considerations had predicted that with sufficiently short pulses useful diffraction data can be collected before the onset of significant radiation damage that ultimately results in Coulomb explosion of the sample. This has been shown recently at the first hard X-ray FEL, the LCLS at Stanford. High resolution data collected of a stream of microcrystals of the model system lysozyme agree well with conventional data collected of a large macroscopic crystal [1] With the demonstration that de-novo phasing is feasible [2], serial femtosecond crystallography has been established as a useful tool for the analysis of tiny crystals [3] and thus the large group of proteins that resist yielding macroscopic crystals such as membrane proteins. In addition to ensure the required fast exchange of the microcrystals upon exposure, liquid jet delivery has the advantage of allowing data collection at room temperature. As demonstrated recently, this is important since structural dynamics and thus the observed conformation is often temperature dependent. Recent results will be described.
Structural Genomics of Chromatin Regulators for Biological Discovery & Epigenetic Therapy
Authors: Arrowsmith Cheryl
Published: November 2015

We are taking a protein family approach to understand how human protein domains, enzymes and complexes recognize specific histone tail sequences and their posttranslational modifications. These are key mechanisms of nuclear signaling that regulate epigenetic cellular states and gene expression programs. Systematic structural and biochemical analyses are revealing key features of selectivity and regulation among these factors, enabling structure-based development of potent, selective, cell-active small molecule inhibitors of individual epigenetic regulatory proteins.
The Experience of "Voyage dans le cristal" Travelling Museum Exhibition
Authors: Hodeau Jean-Louis
Published: November 2015

Crystallography is little-known to the public, even though it underpins much of research into matter in physics, chemistry, new materials and life sciences. On one side, crystallography is present in almost every field of scientific or technical activity and innovative applications. On the other side, origins of crystallography start from humanity's interaction and interrogation with crystals from prehistoric times to the present day. We can use these two characteristics to focus interest large publics on crystallography and show young pupils and students the importance of the scientific approach. To introduce Crystallography to a large public in the World, scientists and scientific organisations from the Steering Committee for the International Year of Crystallography in France and from the Grenoble "100 years of crystallography" group, have joined forces to create a set of multilingual hands-on travelling exhibitions. The complete version of this exhibition exists in English, French and Spanish and is planned in Arabic, Russian, and several other languages. For smaller events, a short version of this exhibition already exists in Flemish, French, Russian, Swedish, Arabic, English, Slovakian and many other languages. Now, they are taking to the road and several destinations have been programmed for 2014 in Africa, Asia, Europe and America. This travelling exhibition entitled "Journey into the Crystal" takes visitors on a journey of discovery of matter – but also on a journey through time to the beginnings of crystallography. Through this Journey into the Crystal, the public discover why crystal intrigues people so much, why it is so useful to science and why it plays such an important role in our daily lives. Learn about the birth of crystallography and the multiple facets of crystals: · An object of beauty · An object for science that brings us essential knowledge about matter · A contemporary object with numerous applications.
The expanding scope of crystallographic representational analysis
Authors: Campbell Branton , Stokes Harold
Published: November 2015

The characterization of a distorted crystal structure, such as might arise from a symmetry-lowering phase transition, is often enhanced by the use of a symmetry-motivated parameter set obtained from group representation theory. These "symmetry-mode" parameters effectively reorganize the traditional parameters (e.g. atomic coordinates, magnetic moments, site occupancies, and cell parameters) that describe how the distorted structure differs from its high-symmetry parent. Representational analysis has been an important facet of crystallography for over 75 years now, particularly as it relates to continuous phase transitions and magnetic structures. The growing interest in the subject today follows on the heels of greatly expanded capabilities, a broader range of applications, and more accessible resources. In this context, I will review key developments that have led us to the present state of the art, explore exciting examples from the current literature, and demonstrate that representational analysis is an area rich with opportunities to innovate.
Protein Structures Related to Diseases
Authors: Sharma Amit
Published: November 2015

Malaria continues to be a major cause of morbidity and mortality throughout the world. Our laboratory uses multi-disciplinary techniques within modern biology - including biochemistry, bioinformatics, cell biology, parasitology and protein crystallography to unravel the mechanism of action of important parasite proteins. Over the past few years, we have made significant progress in understanding various parasite motors involved in protein translation machinery. We have also explored structure-based inhibitor discovery routines against several malaria parasite targets. We will explore examples from our studies that highlight attributes of malaria proteins that can be exploited for discovering new inhibitors.
Triumphs of Crystallography in Tackling HIV/AIDS: Drugs by Design
Authors: Arnold Eddy
Published: November 2015

Crystallography has made extraordinary contributions to our understanding of the biology and chemistry of HIV. Judicious applications of structure-based drug design against HIV-1 protease and reverse transcriptase (RT) has led to the discovery of key drugs that are used in combinations to treat HIV infection. Extensive research and development efforts by pharma, academia, and government have made it possible for an HIV-infected person to live a nearly normal life. I will summarize the elegant structures that have been determined of components of HIV, with an emphasis on the enzyme RT, which my laboratory has studied since 1987. HIV-1 RT is responsible for converting the viral 10-kilobase single-stranded RNA genome to double-stranded DNA. This fascinating and essential enzyme is the target of 13 approved anti-AIDS drugs: 8 nucleoside analog RT inhibitors (NRTIs) and 5 non-nucleoside RT inhibitors (NNRTIs). We have determined crystal structures of wild-type and drug-resistant RTs in complexes with nucleic acid and/or inhibitors. We participated in structure-guided discovery and development of two anti-AIDS drugs with exceptional potency against drug-resistant variants. Crystal structures combined with biochemical data help to elucidate intriguing molecular mechanisms by which HIV-1 develops resistance to different anti-AIDS drugs. Recent crystallographic fragment screening has revealed new allosteric inhibitory binding pockets for future drug discovery. I am very grateful to my many co-workers, colleagues, and friends for their contributions, synchrotron resources at CHESS, BNLS, and APS, and generous funding from NIH in support of research on HIV-1 RT.