Diffuse Streaks Research Articles

Spin liquid in a single crystal of the frustrated diamond lattice antiferromagnet CoAl2O4

We study spin liquid in the frustrated diamond lattice antiferromagnet CoAl2O4 by means of single crystal neutron scattering in zero and applied magnetic field. The magnetically ordered phase appearing below TN=8 K remains nonconventional down to 1.5 K. The magnetic Bragg peaks at the q=0 positions remain broad and their profiles have strong Lorentzian contribution. Additionally, they are connected by weak diffuse streaks along the <111> directions. These observations are explained within the spiral spin liquid model as short-range magnetic correlations of spirals populated at these finite temperatures, as the energy minimum around q=0 is flat and the energy of excited states with q=(111) is low. The agreement is only qualitative, leading us to suspect that microstructure effects are also important. Magnetic field significantly perturbs spin correlations. The 1.5 K static magnetic moment increases from 1.58 mB/Co at zero field to 2.08 mB/Co at 10 T, while the magnetic peaks, being still broad, acquire almost Gaussian profile. Spin excitations are rather conventional spin waves at zero field, resulting in the exchange parameters J1=0.92(1) meV, J2=0.101(2) meV and the anisotropy term D=-0.0089(2) meV for CoAl2O4. The application of a magnetic field leads to a pronounced broadening of the excitations at the zone center, which at 10 T appear gapless and nearly featureless.

Neutron scattering study of acoustic phonon softening in BiVO4

Inelastic neutron scattering has been used to study the transverse acoustic (TA) phonon propagating on the (0,0,1) plane polarized on this plane in BiVO${}_{4}$ above the ferroelastic phase transition at $T$${}_{c}$$=528$ K. The energies of the TA phonon dispersion curve along $[0.7\ensuremath{\xi},\ensuremath{\xi},0]$ are slightly lower than those along $[\ensuremath{\xi},\ensuremath{\xi},0]$, indicating that the acoustic symmetry direction deviates from the high-symmetry $[\ensuremath{\xi},\ensuremath{\xi},0]$ direction. The $[0.7\ensuremath{\xi},\ensuremath{\xi},0]$ TA branch softens in a limited range $\ensuremath{\xi}\ensuremath{\lesssim}0.2$ as the temperature approaches $T$${}_{c}$ from above. The gradual decrease in the initial slope of the $[0.7\ensuremath{\xi},\ensuremath{\xi},0]$ TA branch is quite different from the complete softening of the TA mode reported from Brillouin scattering measurements. A temperature-dependent central peak is associated with the $[0.7\ensuremath{\xi},\ensuremath{\xi},0]$ TA mode. Furthermore, an elastic diffuse streak along $[1,\overline{1},0]$ exists up to 878 K. These precursor effects are discussed in connection with the TA phonon softening.

A new class of 2-(4-cyanophenyl amino)-4-(6-bromo-4-quinolinyloxy)-6-piperazinyl (piperidinyl)-1,3,5-triazine analogues with antimicrobial/antimycobacterial activity

This study presents the synthesis and in vitro pharmacological evaluations of novel 2-(4-cyanophenyl amino)-4-(6-bromo-4-quinolinyloxy)-6-piperazinyl (piperidinyl)-1,3,5-triazines. The title compounds were assayed for their in vitro antimicrobial activity against eight bacteria (Staphylococcus aureus, Bacillus cereus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Salmonella typhi, Proteus vulgaris, Shigella flexneria) and four fungi (Aspergillus niger, Aspergillus fumigatus, Aspergillus clavatus, Candida albicans) using paper disc diffusion and agar streak dilution method as well as against Mycobacterium tuberculosis H37Rv strain using BACTEC MGIT and Lowenstein-Jensen MIC method. The bioassay results indicate that nine compounds namely 5d, 5h, 5n, 5p, 5q, 5r, 5s, 5t and 5u could be considered as possible potential agents with dual antimicrobial and antimycobacterial activities. The structures of the compounds were elucidated with the aid of IR, 1H NMR, 13C NMR, 19F NMR spectroscopy and CHN analysis.

Lattice modulation and superelasticity in oxygen-added β-Ti alloys

The microstructure and martensitic transformation behavior of (Ti–23Nb)–1.0O (at.%) alloy have been closely and systematically investigated by transmission electron microscopy (TEM). Diffuse streaks along the 〈110〉β∗ directions with intensity maxima at 1/2 positions between basal spots are observed in selected area diffraction patterns obtained from the β phase. The streaks correspond to six variants of {110}β〈11¯0〉β transverse lattice modulation caused by randomly distributed oxygen atoms and their local strain fields. Nanosized modulated domains (nanodomains) in the β phase are confirmed in dark field micrographs. These nanodomains act as local barriers to martensitic transformation, thereby suppressing long-range martensitic transformation in the (Ti–23Nb)–1.0O alloy. We suggest a new mechanism for superelasticity in oxygen-containing β-Ti–Nb alloys based on the results of in situ X-ray diffraction measurements and in situ TEM observations.

(Bi9)4[Bi3Pb9Br47]: Probing the limits of the concept “crystal”

The bismuth-rich subbromide Bi39Pb9Br47 = (Bi95+)4[Bi3Pb9Br47]20– was crystallized from a melt of bismuth, lead, and BiBr3. X-ray diffraction on several crystals revealed a (predominantly) monoclinic structure (space group C2/m, no. 12) with lattice parameters a = 18.832(1) Å, b = 18.961(1) Å, c = 36.355(2) Å and β = 97.51(1)°. The unit cell, which contains C4v-symmetric Bi95+ polycations and a complex bromido-plumbate(II)-bismuthate(III) framework, can be interpreted as one layer, which for the most part follows the tetragonal layer symmetry p4/mbm. The stacking of the layers along [001] lowers the symmetry of the structure. The high pseudosymmetry causes local disorder as well as twinning with partial pseudo-coincidence along the tetragonal c-axis. Due to small domain sizes diffuse scattering occurs. Weak maxima on the diffuse streaks can be assigned to an emergäing superstructure with a period of two layers and orthoärhombic symmetry, which corresponds to a repetitive polysynthetic twin with domain size of one unit cell only.

On the Nature of the Multiple Ground States of the MMX Mixed-Valence Chain Compound, [PtII/III2(n-PenCS2)4I]∞

We present a comprehensive study of the temperature dependence of the crystal structure using single-crystal X-ray diffraction and diffuse scattering, and electrical transport and magnetic properties as well as some optical properties at room temperature to elucidate the origin and the form of multiple ground states demonstrated in a previous study of the heat-capacity of the MMX chain compound, [Pt(II/III)(2)(n-PenCS(2))(4)I](∞). The present results confirm the presence of the two phase transitions, one reversible of first order at 207 K and the other nonreversible monotropic at 324 K, separating the low temperature (LT), room temperature (RT), and high temperature (HT) phases. The unit cell displays a 3-fold periodicity of -Pt-Pt-I- in the RT and HT phases because of the structural disorder which is exhibited by the dithiocarboxylato groups and the n-pentyl groups belonging to the central diplatinum unit. In addition, for the HT-phase all the dimers show this disorder. This compound undergoes a metal-semiconductor transition at T(M-S) = 235 K. The presence of diffuse streaks corresponding to 2-fold -Pt-Pt-I- periodicity in the HT and RT phases indicates dynamic valence ordering of the type -Pt(2+)-Pt(2+)-I(-)-Pt(3+)-Pt(3+)-I(-)-or-Pt(2+)-Pt(3+)-I(-)-Pt(3+)-Pt(2+)-I(-)-. For the LT-phase the diffuse scattering is condensed into clear Bragg diffraction peaks while keeping the 3-fold periodicity. This fact suggests further localization through dimerization of charges and spins confirming the diamagnetic state in the magnetic susceptibility and the low electrical conduction below 207 K. The present results are further discussed in relation to those of previous studies on the homologues, [Pt(II/III)(2)(RCS(2))(4)I](∞), R = methyl, ethyl, n-propyl, and n-butyl.

Direct observation ofB-site cation displacements in Pb-based complex perovskite relaxor oxides

Electron diffraction patterns recorded using a scanning transmission electron microscope (STEM) from PbMg1/3Nb2/3O3(PMN) crystallites and PbZn1/3Nb2/3O3(PZN) crystals show weak and systematic continuous diffuse streaking along the 〈110〉 directions. Detailed high-angle annular dark-field (HAADF) images recordedviaan aberration-corrected STEM show that theB-site cations in PMN and PZN undergo correlated and long-range displacements towards the Pb2+ions on the (110) planes. The planarB-site displacement measured from the centres of the octahedra is about 0.3–0.5 Å in PMN and about 0.20–0.4 Å in PZN. In the HAADF images of the PMN crystallites and PZN crystals studied, there is insufficient evidence for systematic long-range planar displacements of the Pb2+ions. The observed Pb2+ion displacements in PMN and PZN appear randomly distributed, mostly displaced along 〈110〉 towards theB-site columns. There is also evidence of possible stress-related distortion in certain unit cells of PMN. In the relaxors studied, two distinct types of displacements were observed: one is the long-range planarB-site spatial displacement on the (110) planes, correlated with the Pb2+ions, possibly resulting in the observed diffuse streaking; the other is short-range Pb2+ion displacement on the (110) planes. The observed displacement status indicates a mutual attraction between the Pb ions and theB-site cations in which theBsites undergo the largest spatial displacements towards the Pb ions along 〈110〉.

Diffuse scattering study of aspirin forms (I) and (II)

Full three-dimensional diffuse scattering data have been recorded for both polymorphic forms [(I) and (II)] of aspirin and these data have been analysed using Monte Carlo computer modelling. The observed scattering in form (I) is well reproduced by a simple harmonic model of thermally induced displacements. The data for form (II) show, in addition to thermal diffuse scattering (TDS) similar to that in form (I), diffuse streaks originating from stacking fault-like defects as well as other effects that can be attributed to strain induced by these defects. The present study has provided strong evidence that the aspirin form (II) structure is a true polymorph with a structure quite distinct from that of form (I). The diffuse scattering evidence presented shows that crystals of form (II) are essentially composed of large single domains of the form (II) lattice with a relatively small volume fraction of intrinsic planar defects or faults comprising misoriented bilayers of molecular dimers. There is evidence of some local aggregation of these defect bilayers to form small included regions of the form (I) structure. Evidence is also presented that shows that the strain effects arise from the mismatch of molecular packing between the defect region and the surrounding form (II) lattice. This occurs at the edges of the planar defects in the b direction only.

TADPOLE GALAXIES IN THE HUBBLE ULTRA DEEP FIELD

Tadpole galaxies have a head-tail shape with a large clump of star formation at the head and a diffuse tail or streak of stars off to one side. We measured the head and tail masses, ages, surface brightnesses, and sizes for 66 tadpoles in the Hubble Ultra Deep Field (UDF), and we looked at the distribution of neighbor densities and tadpole orientations with respect to neighbors. The heads have masses of 10^7-10^8 Msun and photometric ages of ~0.1 Gyr for z~2. The tails have slightly larger masses than the heads, and comparable or slightly older ages. The most obvious interpretation of tadpoles as young merger remnants is difficult to verify. They have no enhanced proximity to other resolved galaxies as a class, and the heads, typically less than 0.2 kpc in diameter, usually have no obvious double-core structure. Another possibility is ram pressure interaction between a gas-rich galaxy and a diffuse cosmological flow. Ram pressure can trigger star formation on one side of a galaxy disk, giving the tadpole shape when viewed edge-on. Ram pressure can also strip away gas from a galaxy and put it into a tail, which then forms new stars and gravitationally drags along old stars with it. Such an effect might have been observed already in the Virgo cluster. Another possibility is that tadpoles are edge-on disks with large, off-center clumps. Analogous lop-sided star formation in UDF clump clusters are shown.

Use of zinc oxide nano particles for production of antimicrobial textiles

The application of nanoscale materials and structures, usually ranging from 1 to 100 nanometers (nm), is an emerging area of nanoscience and nanotechnology. Synthesis of noble metal nanoparticles for applications such as catalysis, electronics, textiles, environmental protection, and biotechnology is an area of constant interest. Recently, an awareness of general sanitation, contact disease transmission, and personal protection has led to the development of antimicrobial textiles. The development of antimicrobial cotton fabrics using Zinc oxide nanoparticles has been investigated in this present work. The ZnO nanoparticles were prepared by wet chemical method and were directly applied on to the 100% cotton woven fabric using pad-dry-cure method. The antibacterial activity of the finished fabrics was assessed qualitatively by agar diffusion and parallel streak method, quantitatively by percentage reduction test. The topographical analysis of the treated fabric and untreated fabric were studied and compared. The results show that the finished fabric demonstrated significant antibacterial activity against S. aureus in both qualitative and quantitative tests. The SEM analysis revealed the embedding of ZnO nanoparticles in treated fabrics. The wash durability study of the treated fabric was also carried out and found to withstand up to 25 wash cycles. Keywords: Nanoparticles, zinc oxide, antimicrobial finish, wash durability

Quantitative analysis of diffuse X-ray scattering in partially transformed 3C-SiC single crystals

The X-ray scattering of partially transformed 3C-SiC single crystals is considered in detail. Extended diffuse scattering streaks, originating from stacking faults (SFs) lying in the {111} planes, are clearly observed in the wide-range reciprocal-space maps. The intensity distribution along the diffuse streaks is simulated with a model including the contributions of the diffuse scattering originating from the SFs [based on the pioneering theoretical description given by Kabra, Pandey &amp; Lele (1986).J. Mater. Sci.21, 1654–1666], the coherent scattering emanating from untransformed areas of the crystals and all θ-dependent terms that affect the scattered intensity (the layer structure factor, the irradiated volume and the polarization of the beam). The quantitative simulation of the diffuse streaks reveals that the transformation occurs through the glide of partial dislocations and allows one to derive the transformation level. It is shown that the 3C polytype is indeed unstable at high temperature. However, it is further shown that defect-free 3C-SiC single crystals remain stable at temperatures where 3C-SiC is known to be usually unstable (2173 K). The origin of this apparent stability is very likely of kinetic nature,i.e.the lack of crystalline defects inhibits the transformation.

Pattern analysis and interpretation of scattering from short-range order stacking in the layered composite crystal 2H-NaxCoO2·yD2O (x≃ 0.35,y≃ 1.3)

Information about the features of Bragg reflections and/or diffuse streaks was obtained through simulation of a neutron powder diffraction pattern based on the model used in a successful analysis of the superconductor 2H-NaxCoO2·yD2O (x≃ 0.35,y≃ 1.3). Intensity distributions were calculated based on a superstructure expression of a commensurate composite crystal model, where the structures of the CoO2part (a1=b1= 2.82 Å) and the guest (a2 =b2= 3.26 Å) with short-range order stacking are described on a cell ofA=B= 2a1= 31/2a2= 5.64 Å, and with alternate stacking based onc= 4.9 Å. It is shown that the most conspicuous diffuse reflection band corresponds to the main reflection scattering of the guest sheet, with local maxima at half-integer positions of ζ′ based on the stacking distance 2c, and that the Bragg diffraction components of the host and guest are coherent in terms of the peak height at integer ζ′′ based on 4c.

Structure, charge ordering and physical properties of Yb2Fe3O7

The structural and physical properties of the layered Yb2Fe3O7 have been extensively investigated. Transmission electron microscopy (TEM) observations at room temperature reveal the presence of diffuse zigzag-type streaks at 1/3(h h l) running along the c* axis direction, suggesting the presence of a charge ordered state with a shorter coherence length in comparison with that in Lu2Fe3O7. The measurements of magnetization demonstrate that the replacement of Lu3+ by the magnetic Yb3+ ion in this layered system could result in visible effects on the low-temperature magnetic properties: the ferrimagnetic phase transition temperature decreases and an additional magnetic anomaly possibly attributed to antiferromagnetic coupling between Yb and Fe layers appears at around 50 K. Analysis of the dielectric properties shows that the Yb2Fe3O7 material in general has a large dielectric constant of about 5000 at room temperature, and a broader relaxation time distribution in comparison with ErFe2O4.

Doping effect on charge ordered structure in RFe2O4 (R=Lu and Yb)

Doping effects on the charge ordered (CO) structure in RFe2O4 (R=Lu, Yb) were investigated by an energy-filtered transmission electron microscope (EF-TEM), in combination with conventional magnetic measurement. The repalcement of Cu2+ and Co2+ for Fe2+ in RFe2O4 (R=Lu, Yb) destroyed drastically the CO structure. In LuFeCuO4, the CO structure with q=1/3 1/3 1/2 disappear and short-ranged domains consisting of cationic ordering of Fe3+ and Cu2+ ions are formed, which gives rise to characteristic zigzag-shaped diffuse streaks with diffuse spots at the h/3-δ h/3-δ 0-type positions (h: integer, δ=0.06) in reciprocal space. In addition, the magnetic measurement revealed that LuFeCuO4 exhibits a magnetic transition around 50K, which is much lower than the Neel temperature of 250K in LuFe2O4. In YbFeCoO4, clusters consisting of Fe3+ and Co2+ in the triangular lattice are formed and give rise to honeycomb-shaped diffuse streaks.

Sideronatrite, Na2Fe(SO4)2(OH){middle dot}3H2O: Crystal structure of the orthorhombic polytype and OD character analysis

Sideronatrite, Na2Fe(SO4)2(OH) ·3H2O, is a secondary hydrated sulfate occurring in desert areas as the result of pyrite alteration. It is one of the environmental indicators of soil-water processes operating in specific landscapes, and, as a consequence, an important marker of acid mine drainage pollution. Sideronatrite has been demonstrated from its peculiar diffraction pattern to belong to a family of OD structures formed by equivalent layers. In this work, a crystal with weak diffuse streaks proved to be suitable for a single-crystal X-ray diffraction study. The crystal structure was solved by direct methods and refined by full matrix least-squares ( R = 7.4% and R W = 8.0%) in the space group P 212121 with a = 7.265(2), b = 20.522(6), c = 7.120(2) A, V = 1061.5(5) A3, and Z = 4, using 798 reflections with I > 3.0 σ( I ). Sideronatrite is characterized by infinite [Fe3+(SO4)2(OH)]2− octahedral-tetrahedral chains of the type [M(TO4)2φ] running parallel to the c axis. These chains are cross-linked by a columnar system of corner-sharing, Na-distorted octahedra along c to form corrugated sheets parallel to the (010) plane. Adjacent sheets are hydrogen-bonded through water molecules coordinated by Na atoms. The present results allow a complete description of the OD character of the structure, with the derivation of the OD groupoid and MDO polytypes. Finally, chemical and structural relationships are taken into account to explain the possible paragenetic sequence concerning several sulfates associated with sideronatrite.

Antimicrobial effects of probiotic bacteria against selected species of yeasts and moulds in cheese‐based dips

SummaryThe antimicrobial properties of selected probiotic bacteria against Aspergillus niger, Penicillium roqueforti, Fusarium spp., Candida albicans and Saccharomyces cerevisiae were examined. Well diffusion and spot and streak methods showed strong inhibition effect of probiotic bacteria and their metabolites against moulds and minimal effect against yeasts. Among the moulds species tested, the inhibitory effect was strongest against Fusarium spp., moderate against Penicillium roqueforti and minimal against A. niger. All strains of Lactobacillus rhamnosus and L. paracasei subsp. paracasei showed maximum inhibitory effect. When probiotic bacteria and yeasts and moulds were co‐cultured in broth media, strains of L. rhamnosus showed maximum inhibitory effect, whereas L. paracasei subsp. paracasei, L. acidophilus, Bifidobacterium animalis and Propionibacterium showed moderate inhibitory effect against C. albicans. Saccharomyces cerevisiae was minimally controlled by probiotic bacteria. Pre‐grown probiotic bacterial culture metabolites controlled yeasts and moulds more effectively than their freeze‐dried or frozen forms. Adding metabolites of probiotic bacteria (5% w/w) showed an effective control against A. niger, Fusarium spp. and C. albicans during the shelf life of 10 weeks at 4 °C and no colonies of yeasts and moulds were formed on the surface of the dip.

Nanometer-Sized Domain Structures in LuFeMO4 (M = Cu, Co) Revealed by Energy-Filtered Transmission Electron Microscopy

Diluted effect on the charge ordered (CO) structure in dielectric materials LuFeMO4 (M = Cu, Co) were investigated by an energy-filtered transmission electron microscopy (TEM), in combination with a conventional TEM. It is revealed that partial substitution of Cu2 + and Co2 + for Fe2 +in LuFe2O4 destabilized the CO structure. In LuFeCuO4, there exist characteristic zigzag-shaped diffuse streaks and diffuse spots at the h/3-δ h/3-δ 0-type positions (h: integer, δ = 0.06) in reciprocal space, which originate from static cationic ordering of Fe3 + and Cu2 + ions in the triangular lattice. Moreover, real-space images by the energy-filtered TEM revealed that nanometer-sized domain structures with the 5∼10 nm size are formed. In contrast, honeycomb-shaped diffuse streaks were found in LuFeCoO4, in which no domain structures are observed in real-space images.

Monte Carlo Simulation Study of Diffuse Scattering in PZT, Pb(Zr,Ti)O3

Transverse polarized diffuse streaks have been observed in diffraction patterns of Pb(Zr1−x Ti x )O3 (PZT) ceramics for compositions ranging from x = 0.3 (rhombohedral phase) to x = 0.7 (tetragonal phase) including the important morphotropic phase boundary (MPB) region (x = 0.48). The streaks correspond to diffuse planes of scattering in three dimensions, and these are oriented normal to the (cubic) $$ \langle 111\rangle_{c} $$ directions. A Monte Carlo (MC) model has been developed that convincingly reproduces the observed diffraction patterns. In this model, the displacements of Pb ions running in chains along each of the $$ \langle 111\rangle_{c} $$ directions are directed along the chain and are strongly correlated from cell to cell. There is no evidence of lateral correlation. Neighboring chains are essentially independent. At this stage, it is not clear what role the local order revealed by the scattering might play in governing the exceptional piezo-electric properties of the material, but its presence requires the currently accepted models for the average structure to be reassessed.

Single-crystal diffuse scattering studies on polymorphs of molecular crystals. I. The room-temperature polymorphs of the drug benzocaine

The drug benzocaine (ethyl 4-aminobenzoate), commonly used as a local anaesthetic, is a bimorphic solid at room temperature. Form (I) is monoclinic P2(1)/c, while the metastable form (II) is orthorhombic P2(1)2(1)2(1). Three-dimensional diffuse X-ray scattering data have been collected for the two forms on the 11-ID-B beamline at the Advanced Photon Source (APS). Both forms show strong and highly structured diffuse scattering. The data have been interpreted and analysed using Monte Carlo (MC) modelling on the basis that the scattering is purely thermal in origin and indicates the presence of highly correlated molecular motions. In both forms (I) and (II) broad diffuse streaks are observed in the 0kl section which indicate strong longitudinal displacement correlations between molecules in the 031 directions, extending over distances of up to 50 A. Streaks extending between Bragg peaks in the hk0 section normal to [100] correspond to correlated motions of chains of molecules extending along a that are linked by N-H...O=C hydrogen bonds and which occur together as coplanar ribbon pairs. The main difference between the two forms is in the dynamical behaviour of the ribbon pairs and in particular how they are able to slide relative to each other. While for form (I) a model involving harmonic springs is able to describe the motion satisfactorily, as simple excursions away from the average structure, there is evidence in form (II) of anharmonic effects that are precursors of a phase transition to a new low-temperature phase, form (III), that was subsequently found.

Effects of stacking fault on the diffraction intensities of β-FeSi 2

β-FeSi 2 was synthesized by heating mixtures of Si and Fe powder sealed with Na metal and Ar gas in a stainless tube. Diffuse streaks elongated along the a axis were observed in the electron diffraction (ED) patterns of β-FeSi 2 prepared at 873 K in the Na melt. No streaks appeared on the spots indexed by k + l = 2 n ( n: integer), which indicated existence of stacking faults caused by a slip system of (1 0 0)[0 1 1]/2. The powder X-ray diffraction (XRD) patterns of the samples prepared at 873 K for 48 h in the Na melt and at 1173 K for 24 h under reduced Na vapor pressure were analyzed by the Rietveld method with a statistical split-site model based on the stacking fault structure. The powder X-ray diffraction patterns of the samples prepared at 873 K for 48 h in the Na melt and at 1173 K for 24 h in Na vapor which evaporated from a mixture of Na and Si were analyzed by the Rietveld method with a statistical split-site model based on the stacking fault structure. The ratios of the normal stacking layer and stacking fault layer of the samples prepared at 873 and 1173 K were estimated to be 0.95:0.05 and 0.84:0.16, respectively. Main features of the observed powder X-ray diffraction patterns were well reproduced by the calculation based on a general recursion method for calculating diffracted intensities from crystals containing stacking fault.