Photoelectron spectra of powder and single crystalline chromium-copper disulfides

2p _3/2,1/2 Photoelectron spectra of single crystalline specimens of chromium-copper disulfides CuCrS₂ and CuCr_0.85V_0.15S₂ are studied. It is shown that the spectra of single crystalline specimens substantially differ from the corresponding spectra of chromium-copper disulfides in the powder state.     

Influence of electrode rotation on the growth and impedance of a low band gap conducting polymer

Rotation of the electrode during the electrochemical polymerization of delta4,4'-di-cyclopenta[2,1-b;3',4'-b']-dithiophene results in enhanced rates of film growth on the electrode and changes in morphology from dominantly fibrilar to globular structures. The impedance of the resulting films shows their ionic conductivities to be higher than their electronic conductivities. Rotating the electrode during growth enhances electronic conductivities by as much as 2 orders of magnitude, and this is attributed to the dominance of growth of the polymer on the electrode surface (grafting) over the precipitation of material from the diffusion layer.     

13C NMR spectra of liquid crystalline substances in the isotropic,nematic and solid phases

A CP MAS ¹³C NMR spectrum indicates that some liquid crystalline substances containing both cyclohexane and benzene rings have a local molecular motion around the benzene plane in the solid state, and the cyclohexane ring has a rigid conformation. The reorientational diffusion of the whole molecule is also observed in the solid state.     

Infrared spectra of four p-n-alkoxybenzoic acids in the solid,liquid crystalline and isotropic phases*

Infrared spectra of four p-n-alkoxybenzoic acids (C₆C₉) in solid, liquid crystalline and isotropic phases were measured. The intensities of some internal vibrational bands changed abruptly at the various phase transitions. The changes of intensity were found to be dependent on the symmetry of the normal vibrations, and on the mechanism of the phase transitions.     

Synthesis and characterization of two polymorphic crystalline phases and an amorphous powder of nickel(II) bisimidazolate

Nickel(II) bisimidazolate is polymorphic. Depending on the synthetic strategy adopted, two crystalline phases (alpha- and beta-Ni(im)(2)) or an amorphous material of the same composition can be prepared. The thermodynamically stable alpha-Ni(im)(2) phase, which can be prepared in water at elevated temperatures, contains a two-dimensional polymer (of nearly square meshes) with square-planar NiN(4) chromophores and exo-bidentate imidazolate ligands bridging nickel atoms that are ca. 5.73 A apart. The beta-Ni(im)(2) phase can be kinetically stabilized at lower temperatures, but the structural complexity and the lack of single crystals prevented its full structural characterization, even in the presence of an indexed powder diffraction pattern. The spectroscopic features of these crystalline phases are compared with those of the amorphous material.     

Influence of the microstructure and its stability on the electrochemical properties of EMD produced from a range of precursors

The influence of the microstructure and the stable crystal structure on the electrochemical properties of the electrolytic manganese dioxide (EMD) produced from manganese cake (EMD_MC), low-grade manganese ore (EMD_LMO), and synthetic manganese sulfate solutions (EMD_SMS) is reported. X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry/differential thermal analysis, field emission scanning electron microscopy (FESEM), and chemical analyses were used to determine the structural and chemical characteristics of the EMD samples. The charge–discharge profile was studied in 9 M KOH using a galvanostatic charge–discharge unit. All the samples were found to contain predominantly γ-phase MnO₂, which is electrochemically active for energy storage applications. FESEM images show that preparation method significantly influences surface morphology, shape, and size of the EMD particles. In almost all cases, nanoparticles were obtained, with spindle-shaped nanoparticles for EMD_MC, platy nanoparticles in the case of EMD_LMO, and anisotropic growth of tetra-branched star-like nanoparticles of EMD_SMS. These nanoparticles arrange themselves in a near net-like fashion, resulting in porosity of the flakes of EMD during electrochemical deposition. Thermal studies showed loss of structural water and formation of lower manganese oxides. The EMD_MC showed superior discharge capacity of ~280 mAh g^?1 as compared to EMD_LMO (275 mAh g^?1) and EMD_SMS (245 mAh g^?1).     

Highly fluorescent crystalline and liquid crystalline columnar phases of pyrene-based structures

A concept for highly ordered solid-state structures with bright fluorescence is proposed: liquid crystals based on tetraethynylpyrene chromophores, where the rigid core is functionalized with flexible, promesogenic alkoxy chains. The synthesis of this novel material is presented. The thermotropic properties are studied by means of differential scanning calorimetry (DSC), cross-polarized optical microscopy (POM), and X-ray diffraction. The mesogen possesses an enantiotropic Col(h) phase over a large temperature range before clearing. The material is highly fluorescent in solution and, most remarkably, in the condensed state, with a broad, strongly red shifted emission. Fluorescence quantum yields (Phi(F)) have been determined to be 70% in dichloromethane solution and 62% in the solid state. Concentration- and temperature-dependent absorption and emission studies as well as quantum-chemical calculations on isolated molecules and dimers are used to clarify the type of intermolecular interactions present as well as their influence on the fluorescence quantum yield and spectral properties of the material. The high luminescence efficiency in the solid state is ascribed to rotated chromophores, leading to an optically allowed lowest optical transition.     

Trap phosphorescence spectra and lifetimes from crystalline tetramethylcyclobutane-1,3-dithione

Phosphorescence spectra and lifetimes of single crystal tetramethylcyclobutane-1,3-dithione (TMCBDT) have been measured over the temperature range 1.6–30 K. Analysis of the phosphorescence intensities as a function of temperature shows that the emission originates from a series of defect traps. At low-temperature emission is observed from the individual triplet spin sublevels of a deep-lying trap. The influence of spin-lattice relaxation on the decay from this trap is modelled. Highly selective intersystem crossing into two of the triplet sublevels is shown to occur. First-order spin-orbit coupling of various excited singlets to two sublevels of the emissive ³A_u state is suggested as the primary mechanism for S-T intersystem crossing. Evidence is presented that the deepest trap is a thio-dione impurity, probably TMTCBD (tetramethyl-3-thio-1,3-cyclobutanedione).     

The structure of 2,2'-difluorobiphenyl in solid crystalline and liquid crystalline phases

The structure of 2,2-difluorobiphenyl in the solid, crystalline phase has been determined by X-ray diffraction. In this phase the molecules are all in a single conformation having the two fluorine nuclei in a syn -arrangment, with the two ring normals at 58 to one another. The structure of the same molecule, but dissolved in a liquid crystalline solvent has been investigated by NMR spectroscopy. In the liquid crystalline phase there is rotation about the inter-ring bond through an angle phi , with a probability distribution P(phi) which has an absolute maximum at the syn-form with phi about 51 . There is also a second maximum in P(phi) at about 130 , corresponding to the anti-form. The syn- and anti-forms are present in the approximate ratio 0.58:0.42.     

Stability and possible transformations of superfulleride crystalline phases

The results of our calculations describe well the relative stability and possible interconversions of mixed phases of superfullerides with alkali and alkaline-earth dopants for body-centered and face-centered lattices with anionic charge up to 12.L. M. Litvinenko Institute of Physical Organic Chemistry and Coal Chemistry, National Academy of Sciences of Ukraine, 70 ul. R. Lyuksemburg, Donetsk 340114, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 1, pp. 13–16, January–February, 1996. Original article submitted March 14, 1995.     

Electrodeposition of mesoporous semimetal and magnetic metal films from lyotropic liquid crystalline phases

Mesoporous semimetal bismuth film and magnetic metal nickel and cobalt thin films have been electrodeposited from hexagonal or lamellar structured lyotropic liquid crystalline phases with polyoxyethylene surfactant. The liquid crystalline templates are characterized by low-angle X-ray diffraction (XRD) and polarized-light optical microscopy (POM). The metal films are characterized by low-angle and wide-angle XRD, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The magnetic measurements on the mesoporous nickel and cobalt films are shown to have higher coercivity (Hc) than the nonporous polycrystalline films.     

Raman and infrared spectra of crystalline fluoroform

Raman and far-infrared spectra of crystalline fluoroform at temperatures between 20 and 106 K have been recorded. There is no evidence for any solid-state phase transitions, nor for hydrogen bonding. The rich lattice spectra and crystal field splittings suggest that the unit cell is rather large, and possible structures are discussed.     

Raman and infrared spectra of crystalline chloroform

Raman and far-infrared spectra of polycrystalline samples of chloroform at 20 and 80 K are reported. Crystal field spilttings of the intramolecular fundamentals are observed as well as nine Raman and six infrared lattice modes. Spectra are interpreted in terms of a group theoretical analysis based on the molecular and crystal symmetries.     

Approximability of impedance spectra by RC elements and implications for impedance analysis

A commonly used class of impedance spectra validity tests is based on fitting serially connected parallel coupled pairs of resistor and capacitor (RC elements) to a measured impedance spectrum. If the model approximates the spectrum well, the measurement is considered valid. It is considered invalid if approximation is poor. Despite being widely used, theoretical justification is still missing. It is not clear which electrochemical processes could be approximated by such a model and hence, for which processes a poor approximation of the spectrum truly indicates a false measurement, instead of merely a lack of generality of the model. The scope of this paper is to derive from a system theory point of view, which class of systems can be approximated by serially connected RC elements and from that to conclude for which electrochemical systems the mentioned class of validity tests is applicable. Moreover, the results will yield theoretical justification for generalizing the concept of distribution function of relaxation times (DRT) by using positive and negative RC elements so that its benefits can be utilized not only for strictly capacitive, but for any possible non-oscillating electrochemical system.     

Local structure and chemical durability of FeOOH-fixed sodium silicate glass prepared from water glass

A 12M HCl solution of iron oxyhydroxide (a-FeOOH: goethite) was mixed with water glass (18Na₂O^.36SiO₂ ^.46H₂O) at room temperature. The mixture (sol) changed into a dry gel when dried at 25 °C for 120 hours in air. Glass-ceramic and glass samples were prepared when the dry gel was heated for 1-3 hours in an electric furnace at 800 and 900 °C, respectively. The ⁵⁷Fe Mössbauer spectrum of the dry gel is composed of a magnetic hyperfine structure owing to the formation of g-FeOOH (lepidocrocite). By contrast, the ⁵⁷Fe Mössbauer spectrum of glass-ceramic and glasses is composed of paramagnetic Fe(III) with distorted tetrahedral symmetry. This proves that Fe(III) atoms occupy network-forming Si(IV) sites in the FeOOH-fixed sodium silicate glass. A leaching test of the silicate glass in the acid rain simulant composed of HNO₃ (pH 3.5) and H₂SO₄ (pH 3.5) revealed high chemical durability, indicating that Fe(III) is firmly fixed in the glass matrix.     

Growth of anisotropic gold nanostructures on conducting glass surfaces

In this paper, we describe a method for the growth of gold nanowires and nanoplates starting from a bilayer array of gold seeds, anchored on electrically conducting indium tin oxide (ITO) substrates. This is based on a seed-mediated growth approach, where the nanoparticles attached on the substrate through molecular linkages are converted to nanowires and nanoplates at certain cetyltrimethylammonium bromide (CTAB) concentration. Our modified approach can be used to make nanowires of several tens of micrometers length at a lower CTAB concentration of 0.1 M. The length of the nanowires can be varied by adjusting the time of the reaction. As the concentration of CTAB was increased to 0.25 M, the nanoparticles got converted to nanoplates. These Au nanoplates are (111) oriented and are aligned parallel to the substrate.     

Transparent glass-ceramics doped with Cr(III): Low-temperature time-resolved spectra and characterization of gahnite and virgilite crystalline phases

Trivalent chromium in transparent glass-ceramics (73.6 SiO₂ :11.8 Al₂O₃:4.2 Li₂O: 7.0 ZnO: 1.6 TiO₂: 1.5 ZrO₂: 0.3 As₂O₃: 0.024 Cr₂O₃ mole%) enters mainly the gahnite phase after an equilibrium has been reached. The intermediate phase during heat treatment is of virgilite-type Li_xAl_xSi_3−xO₆. This glass-ceramic has been studied by X-ray diffraction and time-resolved spectroscopy at low temperatures under laser excitation     

Influence of aspect ratio of carbon nanotubes on crystalline phases and dielectric properties of poly(vinylidene fluoride)

Poly(vinylidene fluoride) (PVDF)-multiwalled carbon nanotube (MWNT) composites with different aspect ratios of MWNT were prepared by a coagulation method. Field emission scanning electron and transmission electron microscopic studies reveal that MWNT are well dispersed in the PVDF matrix. The X-ray diffraction and differential scanning calorimeter data indicate that the composites with high aspect ratio of MWNT have the β phase structure at the MWNT loading level of 2.0wt%, and have a mixture of α and β phase below 2wt% MWNT, and that those composites with low aspect ratio of MWNT, however, always have a mixture of α and β phase for MWNT concentrations ?2.0wt%. The dielectric constant values increase with the increase in MWNT loading level and the percent increase in dielectric constant is much greater in the composite filled with high aspect ratio of MWNT than in that loaded with low aspect ratio. And also, it has been found that the dielectric loss of the composites with MWNT loading level ?2.0wt% is still as low as neat PVDF, which is of significance for dielectric application.