National Institute Of Materials Physics - Romania

Publications

5914 articles found

4631. Dynamic behavior of hybrid organic-inorganic composites: liquid crystals confined in SBA-15 mesoporous materials

Authors: Frunza, L; Kosslick, H; Schonhals, A; Pitsch, I; Frunza, S

Published: 2002, LIQUID CRYSTALS VI, 4799, 238, DOI: 10.1117/12.453885

Molecular dynamics of a nematic liquid crystal, 4n-octylcyanobiphenyl, confined to two types of SBA-type nanoporous molecular sieves were studied by broadband dielectric spectroscopy in order to obtain information about the liquid crystal-surface interactions. The temperature interval of the dielectric measurements was large, covering all the states of the bulk liquid crystal. It is found that there are several relaxation processes covering the large frequency range. A bulk-like relaxation comes from the liquid crystal molecules located in the center of the pores, which rather do not feel the effect of the pore walls. Another relaxation comes from the molecules located in the surface layer. The latter process is much slower than the bulk-like relaxation. The differences observed between the dynamic behavior of the liquid crystal confined to the two types of nanoporous materials are related to pore size, pore shape and liquid crystal-surface interactions.

4632. Electrosynthesis and properties of some substituted polyanilines in phosphate buffer

Authors: Sima, M; Buda, M; Vasile, E; Visan, T

Published: JAN-FEB 2002, REVUE ROUMAINE DE CHIMIE, 47, 193, DOI:

The electropolymerizations of 2-aminohippuric acid methyl ester and 2-aminobenzoic acid methyl ester monomers in phosphate buffer (pH = 6.5) were studied. The formation of thin films at the platinum electrode surface is observed as main product and the electrosynthesis process of the two substituted polyanilines shows the voltammetric characteristics of the polyaniline film electrosynthesis. The necessary charge to deposit 0.05 mum poly(2-aminohippuric acid methyl ester) or poly(2-aminobenzoic acid methyl ester) films is about 60 mC/cm(2). The polymer films were investigated by electrochemical impedance spectroscopy. On the basis of the obtained results we propose the equivalent circuit for these polymer films.

4633. Quasi-optical dynamical surface resistance characterization of HTS laser ablated films

Authors: Branescu, M; Jaklovszky, J; Ristoscu, C; Mihailescu, IN

Published: 2002, ALT'01 INTERNATIONAL CONFERENCE ON ADVANCED LASER TECHNOLOGIES, 4762, 246, DOI: 10.1117/12.478643

The paper presents a syntheses of the last data concerning the optimal parameters of the deposition process to obtain the best dynamic quality HTS thin films in connection with the most precise dynamic measurement method known to date. The paper makes a comparison between the performances achieved by the classical dynamical surface resistance nondestructive measurement techniques of the HTS laser ablated thin films and the quasi-optical high performances one.

4634. Synthesis and structure of trinuclear iron acetate [Fe3O(CH3COO)(6)(H2O)(3)][AuCl4]center dot 6H(2)O

Authors: Turte, KI; Shova, SG; Meriacre, VM; Gdaniec, M; Simonov, YA; Lipkowski, J; Bartolome, J; Wagner, F; Filoti, G

Published: JAN-FEB 2002, JOURNAL OF STRUCTURAL CHEMISTRY, 43, 117, DOI: 10.1023/A:1016082018299

Iron acetate of composition [Fe3O(H3COO)(6)(H2O3)][AuCl4].6H(2)O (1) was synthesized and investigated by X-ray diffraction analysis and Mossbauer spectroscopy. The [Fe3O(CH3COO)(6)(H2O)(3)](+) complex cation has a structure typical for mu(3)-O bridged trinuclear ferric compounds with iron atoms lying at the vertices of a regular triangle with an oxygen atom at the center. The iron atoms are each coordinated by 4 oxygen atoms of the four bridging carboxylic groups, the mu(3)-O bridging atom, and the coordinated water molecule in the trans-position to the tatter. In the trinuclear cation, the Fe(Ill) ions are coupled by antiferromagnetic exchange interactions with the exchange parameter J = -29.0 cm(-1) (HDVV model for D-3h symmetry). The specific role of the solvate water molecules in structure formation is discussed.

4635. A model for structures growth by sodium electrodiffusion in quartz crystals

Authors: Enculescu, I; Iliescu, B; Enculescu, M; Covalcica, I

Published: 2002, CRYSTAL RESEARCH AND TECHNOLOGY, 37, 874, DOI: 10.1002/1521-4079(200208)37:8<868::AID-CRAT868>3.0.CO;2-J

Dendritic structures were grown inside the quartz crystal by electrodiffusion of sodium ions from a NaCl layer at the anode. The electric field was applied along the optical axis Z and the structures were grown in the xy plane. An experimental arrangement using a pointed cathode and a graphite plate anode was employed. X ray diffraction analysis shows that the structures' chemical composition is a mixture of sodium silicates. To explain the structures' growth a model is proposed. The model is a bidimensional one. The transport of the particles along the Z axis structural channels by the electric field was taken into account by introducing a probability of generating the particles in the growth plane as a function of the distance to the cathode. The computer generated results and the experimental ones were compared and a good correlation was found.

4636. Selective hydrogenation of unsaturated aromatic compounds upon Pd-Eu/gamma Al2O3 catalysts

Authors: Coman, S; Vasiliu, C; Parvulescu, VI

Published: MAR-APR 2002, REVUE ROUMAINE DE CHIMIE, 47, 362, DOI:

Pd-1wt% Eu/gammaAl(2)O(3) catalysts with different palladium loadings (0, 1, 03 and 0.5 wt%) were prepared by the wetness successive impregnation method. The state of the supported particles and their interaction with the support were evidenced by transmission electron microscopy (TEM) and electron diffraction (SAED) measurements. The deposition of palladium and europium was found to result in a heterogeneous surface. These catalysts were tested in the hydrogenation of the unsaturated aromatic compounds (styrene, divinylbenzene, indene) and the catalytic results were correlated with the TEM and SAED data. On the basis of this. correlation it was concluded that the hydrogenation occurs on both metallic palladium particles and mixed aluminium-europium oxides. Onto metallic particles hydrogenation occurs with radicalic hydrogen atoms while on the oxidic sites with hydrogen spilled over from palladium.

4637. Some experimental results on electrical Ni/Cr contacts on thermoconductive materials

Authors: Morosanu, C; Nedelcu, M

Published: 2002, XXI INTERNATIONAL CONFERENCE ON THERMOELECTRICS, PROCEEDINGS ICT '02, 570, DOI: 10.1109/ICT.2002.1190382

Some Cr, Ni films have been deposited by RF (1.78 MHz) magnetron sputtering onto thermoelectric materials substrates at low temperatures (<100 degreesC). We have found good adherence values (>100 kgf/cm(2)) onto n and p type substrates. Peltier devices prepared from these wafers and tested using the standard procedure (Melcor Corp.) demonstrated good values of various electrical parameters, similar with those obtained using classical contacts. This research proved the possibility of producing good quality Peltier devices using Ni/Cr electrical contacts obtained by a large scale and versatile deposition method.

4638. SIZE-STRAIN ROUND ROBIN: FIRST RESULTS AND THE COMPARATIVE ANALYSIS OF THE MEASUREMENTS

Authors: Balzar, D; Audebrand, N; Daymond, MR; Fitch, A; Hewat, A; Langford, JI; Le Bail, A; Louer, D; Masson, O; Popa, NC; Stephens, PW; Toby, B

Published: 2002, ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 58, C24, DOI: 10.1107/S010876730208604X

4639. Structural and piezoelectric properties of rare earth doped PbTiO3 ceramics

Authors: Dimitriu, E; Boerasu, I; Pereira, M; Gomes, MJM; Tanasoiu, C

Published: 2002, FERROELECTRICS, 273, 2650, DOI:

Structural and piezoelectric properties of PbTiO3 (PT) ceramics materials doped with different rare earth elements were investigated. The basic chemical formula was Pb(0.88)Ln(0.08)Ti(0.98)Mn(0.02)O(3), where Ln stands for rare earth element (Ce, Pr, Gd, Nd). The powders were prepared by conventional ceramic method. All samples showed a tetragonal perovskite structure at room temperature. After sintering, bulk materials with high density were achieved for all compositions. Followed by XRD, the cell evolution and the structural anisotropy depend on the lanthanide ionic radius. The crystallite size was estimated from XRD measurements. Piezoelectric measurements (d(33) and k(p)) were performed using resonance - antiresonance frequencies. Ce-doped PT showed the highest d(33) coefficient (similar to39pC/N), while for the other doped materials d(33) was only of the order 30 pC/N.

4640. Deep levels in as-grown 4H-SiC epitaxial layers and their correlation with CVD parameters

Authors: Pintilie, I; Pintilie, L; Irmscher, K; Thomas, B

Published: 2002, SILICON CARBIDE AND RELATED MATERIALS - 2002, 433-4, 466, DOI:

Nitrogen doped 4H-SiC epitaxial layers grown by hot-wall chemical vapor deposition were investigated by deep level transient spectroscopy in the as-grown state. Besides the Z(1,2) defect level at E-C - 0.66 eV, that seems to be omnipresent, four other electron traps labeled IL1 to IL4 With ionization energies between 0.87 and 1.31 eV could be detected. The dependence of the deep level concentrations on the incorporated N concentration ranging from few 10(14) to Some 10(15) cm(-3) and the C/Si ratio (1.2divided by3) was examined. The concentration of both Z(1,2) and IL1 increases with increasing N doping. For medium C/Si ratios this dependence is linear for Z(1,2) and quadratic for IL1. High C/Si ratios enhance the formation of Z(1,2) while they suppress that of IL1. These results suggest a complex of interstitial C and N on carbon site (C-i-N-C) for Z(1,2) and a nitrogen pair (N-C-N-i) for IL1. However, other possibilities like Si vacancy related defects cannot be ruled out at present.