National Institute Of Materials Physics - Romania

SERS and FTIR spectra of M and S composites, provided by adding of single-walled carbon nanotubes (SWNTs) to the polyaniline (PANI) solution and chemical polymerization of aniline, respectively are different. The difference originates in the irreversible transformation of SWNTs in the polymerization medium. This explains the similarity of SERS and FTIR spectra of PANI/SWNTs and PANI/C-60 composites, chemically synthesized. For M composites, strong hindrance effects are evidenced by band at 773-755 cm(-1) associated to the vibration of deformation of the benzene and quinoid ring. The charge transfer is illustrated for all compounds by absorption band at 1144 cm(-1).

Lead zirconate-titanate (PZT) thin films with Zr/Ti ratio of 92/8 were deposited by sol-gel on Pt(111)-coated Si(100) and single crystal MgO(100) substrates. The films crystallize differently on the two type of substrates: in case of the films deposited on Pt the perovskite structure is established only after oxygen annealing, while for the films deposited on MgO annealing in air is enough. The films are polycrystalline with some preferred orientation that is substrate dependent. Average values of 2.1 muC/cm(2) and 78 kV/cm were obtained for remnant polarization and coercive field, respectively. The I-V characteristic at low to medium voltages is dominated by field enhanced Schottky emission, with Ln(J)similar to(V + V-bi)(1/4) dependence of the current density. A value of about 3.85 eV was estimated for the band-gap from optical measurements.

The paper describes the specific quasi-optical phenomena involved in the generation of the high coherent celestial and biological radiation. It examines the generation mechanism of the high coherent radiation in the living systems in the presence of the ambient celestial primordial isotropic background. Josephson and Kerr mechanisms provide an explanation of the concept of bio-coherence as a novel possibility of electromagnetic communication.

The paper describes the investigations of (Zr0.8Sn0.2)TiO4 compounds prepared by solid-state reaction techniques. The effect of La2O3, ZnO and NiO addition on microwave dielectric properties was investigated. The samples were sintered at temperatures T-s = 1280 divided by 1400 degrees C The inaterials exhibit a dielectric constant epsilon(r) similar to 36 and high values of the Q f productfroin 30,000 to 55,000 at microwave frequencies. The measured temperature coefficient of the resonance frequency tau(f) takes values in the range (-2 divided by+4) ppm/degrees C.

This paper reports an investigation of the gas-sensitive properties of thick film sensors based on mixed nanosized oxides (1-x)alpha Fe2O3-XSnO2 (x = 0.1 - 1.0), towards different reducing gases (CH4, CO, H2O). The samples were tested in the range of temperatures (200-400 degrees C). The mixed oxides proved a real sensitivity to CH4, being practically insensitive to detection limit of CO. The maximum response to CH4 takes place at 330 degrees, where the water interference was also studied.

Molecular dynamics of water confined to some molecular sieves is Studied by broadband dielectric spectroscopy (10(-2) to 10(9) Liz). Faujasite as well as molecular sieves with hexagonal cylindrical pores or cellular structure were used as confining matrix. It was found that the mean relaxation time of confined water has unusual non-monotonic saddle-like temperature dependence. Such temperature dependence was interpreted using a model recently developed by Ryabov et al. [J. Phys. Chem. B 2001, 105, 1845] to analyze the dynamics of water in nanoporous glasses. The unusual behavior is the result Of two competing processes: orientational fluctuations the water molecules following all Arrhenius-like temperature dependence and the formation of the defects necessary for this reorientation. The number of defects decreases with increasing the temperature. The temperature dependence of the relaxation time has been proven to be a quite fundamental phenomenon characteristic for water in confining geometries. The defects involved in the dynamics of confined water might be related to the presence of OH groups as defects of the confining framework.

We report an electron paramagnetic resonance (EPR) investigation of the spin dynamics in the paramagnetic regime of nanosized La0.67Ca0.33MnO3-delta manganites. The temperature dependences of the EPR line width and integral intensity have been analyzed in terms of the bottlenecked spin relaxation and small polaron hopping scenarios. The exchange coupling integral between Mn3+ and Mn4+ ions and the polaron activation energy decrease with the reduction of grain size. A discussion is given concerning the factors which could explain the observed changes.