Small angle neutron scattering from micellar solutions of triton X-100

Micellar solutions of non-ionic surfactant triton X-100 (8% by weight) show phase separation at cloud pointT _cp ～ 335 K. This paper reports results of small angle neutron scattering (SANS) experiments from this solution as a function of temperature between 298 and 332 K. The range of wave-vector transferQ, covered in these experiments is from 0.02 to 0.15 Å^?1. It is seen that as one approachesT _cp, the neutron scattering cross section diverges in the region of lowQ (<0.06 Å^?1) while it is independent of temperature in region of largeQ(>0.06 Å^?1). We believe that the divergence of scattering at lowQ with an increase in temperature is because of changes in the structure factorS(Q) of the solution. The measured distributions have been analyzed using four different models for inter-micellar potential. The models used to calculate the structure factorS(Q) are (1) mean spherical approximation (MSA) with Yukawa tail for attractive potential, (2) MSA with an attractive square well potential, (3) random phase approximation (RPA) with an attractive square-well potential and (4) Sticky hard sphere model (attractive square-well potential with Percus-Yevick approximation). The strengths of the attractive potential required to fit the SANS data are (?6.6 to ? 14.4)/kt for model (1), (? 6.6 to ? 15.0)/kt for model (2), (? 3.8 to ? 7.3)/k _B T for model (3) and (?2 to ?2.7)/kt for model (4). On the basis of reasonableness of the derived strength of the potential near the phase separation temperature and its relative temperature dependence, it is concluded that present data favour the Sticky hard sphere model.     

A new crystalline HMX polymorph: ɛ-HMX

A new crystalline HMX polymorph, ?-HMX, was obtained. ?-HMX crystals were studied by X-ray structure analysis, optical microscopy, and differential scanning calorimetry. Their space group is P2₁/c. The unit cell parameters are a = 21.799(3) Å, b = 10.913(2) Å, c = 10.819(2) Å, and β = 97.43(2)°, V = 2552.15 ų, Z = 4. ?-HMX molecules are not equivalent in crystals and have chair conformations. The heat of the polymorphic transition of ?-HMX into the δ-polymorph was measured. The transition occurred with the intermediate formation of β-HMX. The dependence between the heats of polymorphic transitions and the densities of crystals of various HMX polymorphs was demonstrated. The character of this dependence was to a substantial extent determined by the type of HMX molecule conformation.     

Two new superstructures Ba4Ti5O10 and Ba4Ti4O11 in epitaxial barium titanate nanodomains determined by nanobeam electron diffraction and high-resolution transmission electron microscopy

Barium titanate thin films deposited on MgO (0?0?1) by RF magnetron sputtering are composed of two new superstructures Ba₄Ti₅O₁₀ and Ba₄Ti₄O₁₁ formed as epitaxial nanodomain structures. Due to the nanometre scale size of domains and the complexity of the structure in the film, the single-crystal X-ray diffraction technique does not have the capability for the crystallographic structure determination of the two new superstructures. We used nanobeam electron diffraction to reconstruct the three-dimensional diffraction space and hence the symmetry of the new superstructures. Both Ba₄Ti₅O₁₀ and Ba₄Ti₄O₁₁ are monoclinic structures with a space group of Cm (b-unique axis). Ba₄Ti₅O₁₀ has a lattice parameter a?=?16.49?Å, b?=?3.94?Å, c?=?8.94?Å and β?=?103°, while Ba₄Ti₄O₁₁ has a?=?17.88?Å, b?=?3.94?Å, c?=?7.21?Å and β?=?98°. Atomic structural models for the two new superstructures were established by reconstructing the high-resolution transmission electron microscopy (HRTEM) images taken from the three major axes and refined by matching the simulated HRTEM images and calculated electron diffraction patterns with the experimental results. The two superstructures are epitaxially grown on MgO with their b-axis parallel to the growth direction.     

Universal dynamics behavior in superionic conducting glasses

The inelastic neutron scattering experiment on superionic glass system AgI-AgPO₃ have been performed in the energy and momentum transfer range from ? 5 to 15 meV and 0 to 8 Å^? 1, respectively by using a time of flight MARI instrument at Rutherford Appleton Laboratory, ISIS, UK. The E-dependence of the inelastic data show an excess intensity at low energy around 3 meV, the so-called Boson peak, which increased with the dopant salt. The Q-dependence of the elastic scattering reveals a prepeak at anomalously low Q value around 0.8 Å^? 1, which is not observed in the undoped AgPO₃ glass. The Q-dependence in the energy region from 1 to 3 meV shows clearly an excess intensity at Q ~ 2.2 Å ^? 1compared with the undoped AgPO₃. All these features correlate with the increasing mobility of Ag⁺ ions due to the expansion of the network structure caused by salt doping, which leads to the increase of ionic conductivity. Similar results have also been observed in the corresponding superionic glass system AgI-Ag₂S-AgPO₃ that was observed by both MARI and NEAT instrument at HMI, Berlin. The results show a universal dynamic behavior in silver phosphate glasses.     

X-ray diffraction analysis and occurrence of multiple phases in Bi-Sr-Ca-Cu-O superconductors

Starting composition 1112 for Bi-Sr-Ca-Cu-oxide yields multiphase super-conductors with the proportion of constituent phases depending sensitively on the annealing temperature. The R-T curves show zero resistivity and the transition corresponding toT _c = 80 K phase prominently. However, indexing of X-ray diffraction peaks reveals presence of 80 K (lowT _c) as well as 108 K (highT _c) phase. The lowT _c phase thus corresponds to the orthorhombic structure with a unit cell ofa = 5.4Å,b = 27 Å andc = 30.56 Å. This is further understood to be composed of a pseudotetragonal cell ofa =b = 5.41 Å. The highT _c phase similarly pertains to the orthorhombic structure withc = 36 Å.     

Superparamagnetism and magnetic granulometry of vitroceramics containing iron-lithium ferrite

Magnetic properties of lithium ferrite crystallites distributed in a glassy matrix vary with their average size d: (1) d ? 100 Å: superparamagnetism d and the limits of the distribution have been calculated by fitting magnetisation curves vs applied field. (2) d ? 150 Å: ferrimagnetism with a hysteresis loop maximum for the monodomain size (260 ± 40 Å). (3) 100 ? d ? 150 Å: superposition of the two preceding phenomena.     

In the wonderland of ultra-parallel neutron beams

Bragg reflections from single crystals yield angular widths of a few arcsec for thermal neutron beams. The Bonse-Hart proposal to attain a sharp, nearly rectangular profile by Bragg reflecting neutrons multiply from a channel-cut single crystal, was realized in its totality three and a half decades later by achieving the corresponding Darwin reflection curves for 5.23 Å neutrons. This facilitated SUSANS (Super USANS) measurements in the Q ～ 10^?5 Å^?1 range. The polarized neutron option was introduced into the SUSANS set-up by separating the up- and down-spin neutron beams by ～10 arcsec with a magnetic (air) prism. The neutron angular width has recently been reduced further by an order of magnitude to ～0.6 arcsec by diffracting 5.3 Å neutrons from a judiciously optimized Bragg prism. This constitutes the most parallel monochromatic neutron beam produced to date. I present the first SUSANS spectra probing the Q ～ 10^?6 Å^?1 domain, recorded with this beam.     

Evaluation of NaFeTiO<Subscript>4</Subscript> as an electrode for energy storage application

We report a polycrystalline NaFeTiO₄ prepared via conventional solid-state reaction route. X-ray diffraction (XRD) results and Rietveld refinement confirmed single-phase NaFeTiO₄ having an orthorhombic unit cell with lattice parameters a = 9.17051 Å, b = 2.96310 Å, and c = 10.73676 Å and Pnma space group (No. 62). Energy dispersive spectrum (EDS) yielded sample stoichiometry that agrees well with its molecular formula. The surface morphology indicated a cylindrical rod-like microstructure comprising well-defined grains having variable dimension, i.e., diameter ~?250 to 350 nm and length ~?1 to 5 μm. Vibrational spectroscopy (FTIR/Raman) results indicated presence of FeO₆ and TiO₆ octahedra in good agreement with crystallographic study. Brunner-Emmet-Teller (BET) surface area measurement yielded a specific surface area as high as ~?4.28 m² g^?1. Electrical impedance spectrum indicated presence of grains separated by well-defined grain boundaries in agreement with microstructural analysis. Electrical conductivity of the material was estimated to be ~?6.05 × 10^?6 S cm^?1. The structural model obtained using XRD and vibrational spectrum results suggest layered tunnel/cage structure of cage dimension ~?4.65 Å, along [010] direction in the xz plane, which is larger than the size of Na⁺ ion (0.98 Å). So, easier Na⁺ migration feasibility exists in NaFeTiO₄ crystal lattice making it a good candidate for electrode applications.     

Microwave spectrum,centrifugal distortion,substitution structure,and dipole moment of sulfine,CH2SO

The microwave spectrum of the reactive species sulfine (CH₂SO) has been studied. Assignments of 86 transitions of the ground vibrational state normal isotopic species, with J up to 60, have allowed a thorough centrifugal distortion analysis. With planarity implied by the I_c-I_a-I_b value of 0.1333 amu $\text{A}\text{?}{}^2$, spectral assignments of seven other isotopic modifications have resulted in the following substitution bond lengths and angles: CH_syn = 1.085 Å, CH_anti = 1.077 Å, CS = 1.610 Å, SO = 1.469 Å, ?HCH = 121.86^°, ?SCH_syn = 122.51^°, ?SCH_anti = 115.63^°, and ?CSO = 122.51^°. From Stark effect measurements of the normal and d₂ species, the dipole moment has been determined to be 2.994 D, oriented 25.50° relative to the SO bond and 9.61° relative to the normal species “a” axis. At an initial pressure of 30 mTorr in a clean brass waveguide, the lifetime of sulfine at 25°C is ～30 min.     

The effect of Cu on precipitation in Al–Mg–Si alloys

TEM investigations of two alloys isothermally heat treated at 175°C and 260°C show how Cu additions to the Al–Mg–Si system affect precipitation. Both alloys had a solute content Mg?+?Si?=?1.3 at.%, 0.127 at.% Cu, but with Mg/Si 0.8 and 1.25. Cu-containing Guinier-Preston (GP) zones and three types of Q′ precursors are identified as most common phases at peak-hardness conditions, whereas β″ accounts for maximum 30% of the total number of precipitates. The precursors have needle (L and S precipitates) or plate (C precipitate) morphologies. They consist of different arrangements of Al, Mg and Cu atoms on a grid defined by triangularly arranged Si planes parallel with and having the same period as {100} Al planes. The Si grid is composed of nearly hexagonal sub-cells of a?=?b?=?4.05?Å, c?=?4.05?Å. The Cu arrangement on the grid is often disordered in the needle precursors. The plate precursor is ordered, with a monoclinic unit cell of a?=?10.32?Å, b?=?8.1?Å, c?=?4.05?Å, γ?=?101°.     

Cation disorder and structural studies on Bi4−x Nd x Ti3O12 (0.0≤x≤2.0)

Here we report the results of combined powder X-ray and neutron diffraction studies of Bi_4?x Nd _x Ti₃O₁₂ (0.0 ≤ x ≤ 2.0) compositions. The parent Bi₄Ti₃O₁₂ has an orthorhombic lattice (space group: B2cb) with unit cell parameters a = 5.4432(5) Å, b = 5.4099(5) Å and c = 32.821(2) Å, and V = 966.5(1) ų. This orthorhombic lattice is retained in all the studied compositions. The unit cell parameters gradually decrease with Nd³⁺ ion concentration with a discontinuity at x = 0.75. Orthorhombicity of the lattice decreases with increase in Nd³⁺ content in the lattice. The orthorhombic unit cell parameters for a representative Bi₂Nd₂Ti₃O₁₂ composition are: a = 5.3834(9), b = 5.3846(9) and c = 32.784(1) Å. The observed orthorhombic distortion at x = 2.0 is very small and thus the crystal structure apparently has a pseudo-tetragonal lattice. In addition, Nd³⁺ preferentially substitutes in the perovskite slab of the Aurivillius structure. The fraction of Nd³⁺ in the fluorite slab increases with increase in Nd³⁺ contents.     

The problem of satellites of spectral lines in the Jabłoński theory

This paper presents a calculation of the intensity distribution of a spectral line perturbed by interactions with foreign atoms. The calculation is based on the statistical version of the Jab?oński theory developed for the Lennard-Jones interaction potential.The calculated line profile shows a distinct satellite on the red wing, at a frequency b and a trace of another band at about 2b, where b is the depth of the difference potential. The positions of these bands are in good agreement with previously reported experimental data for the Hg 2537 Å resonance line broadened by krypton. It is shown that the present method describes both the core of the broadened line and its far red wing with the satellite structure.     

ΔT-window neutron spectrometer

A high resolution neutron spectrometer making use of a ΔT-window filter for the analyser and time-of-flight technique for analysing incident neutron energy has been designed. The spectrometer will provide a continuously variable energy resolution ΔE from 40–50μeV at ∼ 5230μeV. The range of energy transfer allowed is −1450μeV to +2950μeV and the range of wavevector transferQ allowed is 0·82–3·06 ?⁻¹. Depending on the resolution used, the counting rates are expected to vary from 28–60 × 10³ counts/hr if one assumes 10% isotropic elastic scattering from the sample.     

Syntheses and structure characterization of inorganic/organic coordination polymers: Ag(dpa), Co(O3PH)(4,4′-bpy)(H2O), Zn(O3PH)(4,4′-bpy)0.5 and Mn[O2PH(C6H5)]2(4,4′-bpy) (dpa=2,2′-dipyridylamine; 4,4′-bpy=4,4′-bipyridine)

Four novel coordination polymers: Ag(dpa) I, Co(O₃PH)(4,4′-bpy)(H₂O) II, Zn(O₃PH)(4,4′-bpy)_0.5 III and Mn[O₂PH(C₆H₅)]₂(4,4′-bpy) IV (dpa=2,2′-dipyridylamine; 4,4′-bpy=4,4′-bipyridine), were synthesized by microwave heating and characterized by X-ray crystallography. I crystallizes in monoclinic space group P21/n with a=11.576(2) Å, b=5.585(2) Å, c=15.243(4) Å, β=109.00(2)°, V=931.8(3) ų. II crystallizes in monoclinic Cc space group with a=22.477(7) Å, b=5.280(1) Å, c=10.404(4) Å, β=96.08(3)°, V=1227.8(7) ų. III crystallizes in monoclinic P21/c space group with a=9.758(2) Å, b=7.449(3) Å, c=10.277(2) Å, β=100.02(2)°, V=735.6(4) ų. IV crystallizes in monoclinic space group P2/c with a=10.174(1) Å, b=11.817(3) Å, c=18.784(4) Å, β=102.14(1)°, V=2207.8(8) ų. I consists of linear metal–metal chains wrapped by dpa ligands. II and III consist of two-dimensional M^II(O₃PH) inorganic sheets cross-linked by 4,4′-bpy ligands, while IV is formed by Mn[O₂PH(C₆H₅)]₂ sheets cross-linked by 4,4′-bpy ligands. I exhibits two-step thermal decomposition at ~200 and ~250°C, resulting in the reduction of Ag⁺ to Ag metal. II loses its coordination water at ~100°C, leaving vacant coordination sites at Co²⁺ ions, while the original framework remains intact. The removal of 4,4′-bpy in II–IV occurs at elevated temperatures above 250, 200 and 400°C respectively.     

Thin ferroelectric Nd-doped BiFeO<Subscript>3</Subscript> films with orthorhombic structure

X-ray diffraction and Raman spectroscopy of epitaxial Nd-doped bismuth ferrite films on MgO substrates reveal their orthorhombic symmetry Fmm2 (a = 7.914 Å, b = 7.913 Å, and c = 7.937 Å).     

Electric moments of the first excited state of 18O

The static quadrupole moment Q_2⁺ and the B(E2; 0⁺ → 2⁺) value of the first excited state of ¹⁸O at e_x = 1.982 MeV have been determined using the reorientation effect in Coulomb excitation. Surface-barrier detectors at laboratory angles of 90° and 174° were used to detect ¹⁸O ions elastically and inelastically scattered from ²⁰⁸Pb. At both angles, we determined experimentally the maximum bombarding energies at which nuclear interference effects were negligible. It is found that Q_⁺ = ?0.023 ± 0.021 e · b (?0.052 ± 0.021 e · b) for destructive (constructive) interference from higher states. This result is in good agreement with theoretical expectation. For the transition moment we find B(E2; 0⁺ → 2⁺) = 0.00390 ± 0.00018 e² · b² (0.00371 ± 0.00018 e² · b²) for destructive (constructive) interference.     

A new crystalline form of carbon based on the C36 fullerene: Simulating its crystal and electronic structure

A new crystalline allotropic form of carbon consisting of covalently bound fullerenes C₃₆ of symmetry D _6h is suggested. The structure of the unit cell of this compound was simulated. The unit-cell parameters obtained (a=b=6.695 Å and c=6.763 Å) are close to experimental data. The band structure of the spectrum of valence electrons was calculated by the method of crystal orbitals. The bandgap was found to be ～1.9 eV. The energy-band structure of quasi-one-dimensional macromolecules [C₃₆]_n(n?1) is discussed depending on the way in which the monomers are bound in them.     

Pressure induced phase transition in mercurous chloride

Pressure induced phase transition in mercurous chloride has been studied by high pressure x-ray diamond anvil cell. The change in diffraction pattern started and ended at a pressure of about 5 kbar and 20 kbar respectively. The patterns recorded at 20 kbar could be indexed basing on an orthorhombic lattice, with lattice parametersa=4.23 Å,b=4.54 Å andc=10.44 Å.     

Neutron-interferometric measurement of the coherent scattering length of the isotopes of silver

Employing a new measuring scheme with the D 18 Neutron Interferometer at the ILL, Grenoble, the thermal neutron coherent scattering lengthb _c for bound atoms of natural Ag,¹⁰⁷Ag and¹⁰⁹Ag have been measured at the wavelengthλ=1.8742 Å. The results, corrected for composition and density of the actual samples, are nat Ag:b _c =5.922 (7) fm¹⁰⁷Ag:¹⁰⁷ b _c =7.555 (11) fm¹⁰⁹Ag:¹⁰⁹ b _c =4.165 (11) fm The result is in agreement with an earlier value obtained with the interferometer for nat Ag (5.932 (6)) using a different measuring scheme and a totally different sample. For nat Ag and¹⁰⁷Ag the values determined interferometrically are ?0.05 and ?0.08 fm smaller, repectively, than those measured with the Christiansen filter method.     

Anomalously high electric field gradients for Hg in Zn,Cd and Re below 0.05 K

Nuclear orientation and time differential perturbed angular correlation studies of the electric quadrupole interaction of Hg in Zn, Cd and Re have been performed. The interaction frequencies found in the nuclear orientation experiments for ^197mHg below 0.05 K, ν_Q = +480(20) MHz, ν_Q = +430(30) MHz and ν_Q = ?110(15) MHz in Zn, Cd and Re, respectively, are a factor of about 4 higher than expected from the extrapolation of angular correlation data available down to 105 K.