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ternary sulfides. Neutron diffraction data from powders was collected on the 3T2 diffractometer at the Laboratoire LØon Brillouin, Saclay, France, to follow the crystal and magnetic structures of the title compound as a function of temperature. Rietveld refinements made use of the FullProf Rietveld program [18].Variable-temperature Mössbauer spectra with good statistics were measured from 300 K down to 4.2 K using a source of 57 Co in rhodium. The data were collected with the sample in a helium cryostat. The program MOSFUN [19] was used to analyze the data.First principles calculations of the electronic structures were performed using the LMTO-ASA method. A detailed description of the LMTO-ASA method, including its applications, can be found elsewhere [20]. The scalar± relativistic Kohn Sham equations were solved, taking all relativistic effects into account except for spin±orbit coupling. The basis set included the s, p, and d wavefunctions for Fe, Cu, Cr, and S. The S d wavefunctions were treated using the down-folding procedure. The k integrated functions were evaluated by the tetrahedron method on a grid of 735 k points in the irreducible part of the Brillouin zone (1/48 of the BZ). We used lattice constants from the neutron diffraction refinement and constructed a supercell with an ordered arrangement of Fe and Cu on the tetrahedral sites in the space group F43m. For comparison, we have also performed calculations on the end members in the series, that is FeCr 2 S 4 and CuCr 2 S 4 .Because of magnetic ordering, the calculations were performed (using the von Barth±Hedin [21] form of the exchange correlation within the local spin density approximation) with the assumption of a magnetic ground state (spin-polarized calculation) as these, in agreement with experiment, yielded more stable total energies.

Hybrid organic-inorganic ionic conductors, also called ormolytes (organically modified electrolytes), were obtained by dissolution of LiClO 4 in siloxane-poly(propylene glycol) matrixes. The dynamic features of these nanocomposites were studied and correlated to their electrical properties. Solid-state nuclear magnetic resonance (NMR) spectroscopy was used to probe the effects of the temperature and nanocomposite composition on the dynamic behaviors of both the ionic species ( 7 Li) and the polymer chains ( 13 C). NMR, dc ionic conductivity, and DSC results demonstrate that the Li + mobility is strongly assisted by the segmental motion of the polymer chain above its glass transition temperature. The ac ionic conductivity in such composites is explained by use of the random free energy barrier (RFEB) model, which is in agreement with their disordered and heterogeneous structures. These solid ormolytes are transparent and flexible, and they exhibit good ionic conductivity at room temperature (up to 10 -4 S/cm). Consequently, they are very promising candidates for use in several applications such as batteries, sensors, and electrochromic and photoelectrochemical devices.

The ac complex conductivity σ*(f) of polyaniline (PAN) films at different doping levels and different temperatures, in the 1–100 KHz frequency range, are reported. The results are typical of a disordered medium where the real component of ac conductivity is frequency independent at low frequencies, rising for higher values of frequencies. In order to interpret both the real and the imaginary components of σ*(f), we developed a model which considers the doped PAN as a disordered insulating matrix, sprinkled with conductive islands generated by doping, as indicated by energy dispersed x-ray microanalysis. The conduction through the insulating matrix obeys the random free energy barrier model, while in the conductive islands a metallic frequency-independent conductivity is considered. From the fittings we obtained the activation energy value of the maximum energy barrier of the doping mechanism and estimated the concentration of hopping sites.

A method for direct in situ thickness measurements of ultra-thin soft polymer films is presented in which an atomic force microscope (AFM) tip is used to create a furrow in the film, whereby the thickness is determined by scanning the sample across the furrow with the AFM. The sample does not need to be moved since the scratching and the measurements are performed with the same apparatus. This `furrow method' is applied to layer-by-layer polymer/polyelectrolyte ultra-thin films onto hydrophilic glass and silicon wafer substrates. This procedure is made possible because the polymeric film is less stiff than the substrates and the silicon tip. Results for 10-12-bilayer films are comparable to those obtained from profilometry, whose accuracy is only reasonable for films with more than ten bilayers. Taken together, the AFM and profilometer results show that film thickness increases linearly with the number of bilayers. Furthermore, the film thickness does not seem to depend on the substrate used but only on the number of bilayers deposited.

High molecular weight poly(o‐methoxyaniline) was synthesized using a novel method in which the polymerization occurs in the presence of a neutral salt. The molecular weight of the polymer was greatly affected by the quenching procedure employed to conclude the polymerization. Conventional doping of the base form of poly(o‐methoxyaniline) produced a yellow coloration of the doping solution and polymer degradation. It was found that the molecular weight of the polymer decreased significantly after washing or doping with certain aqueous acid media. The gelation conditions of N‐methyl pyrrolidinone (NMP) solutions and film preparation were also investigated for polymers of various molecular weights. The gelation time in NMP decreased drastically with the increase in the polymer molecular weight (the same for solution concentration and temperature), until a critical point was reached after which its decrease was very slow. Flexible, free‐standing, and stretchable films were readily obtained from the higher molecular weight polymers. Good quality doped gel films with conductivity of up to 1 S/cm were obtained under optimized doping conditions. © 1994 John Wiley & Sons, Inc.

Layer-by-layer (LBL) films of a semiconducting polymer (POMA) alternated with a polyelectrolyte (PVS), adsorbed onto silicon oxide, mica, ITO/glass, Au/Cr/glass, hydrophilic and hydrophobic glass were studied by atomic force microscopy (AFM). The samples were characterized LBL with the AFM operating in the contact, friction and tapping modes, which allowed us to determine their morphological surface properties such as roughness, mean grain size, grain boundaries and power spectrum density. Their film thickness was measured by AFM using the tip as a scraping tool. Surface roughness increases with the number of bilayers until a constant value is reached. This is in agreement with the observed increase in the adsorbed amount (per layer) of POMA as the number of bilayers is increased, which also saturates after several bilayers. It is shown that the 3D growth behaviour indicates a similar microscopic mechanism for all systems under study, pointing to a stochastic growth process of the Eden model type, but strongly influenced by initial roughness and water affinity of the virgin substrates. The crystalline or amorphous nature of the substrates does not seem to influence the growth process.