Publications

Nonlinear materials Y1-xRxCa4O(BO3)(3) (R = Lu or Sc) with 0 < x <= 0.5 were synthesized for the first time. The room temperature X-ray diffraction studies show that Y1-xLuxCa4O(BO3)(3) and Y1-xScxCa4O(BO3)(3) compounds with x < 0.4 and x = 0.4 and x > 0.2, respectively, reveal the presence of extra phases which imply their non-congruent melting and difficulties in crystals growth.

Plasma polymerization has been carried out in a parallel plate RF discharge reactor in mixtures of argon with pentacyclic precursors, namely thiophene, furan and pyrrole. The plasma characterization showed the presence of emission bands peculiar to each monomer. The deposition of highly transparent films with partial conservation of the pentacyclic structure, inclusion of various oligomers, roughness and surface energy depending on the precursor nature was demonstrated by material investigations results. The material conductivity is significantly improved upon iodine doping in the case of polythiophene and polypyrrole-like films, while an opposite behavior was observed for the polyfuran-like films.

(Bi0.5Na0.5)TiO3 doped with 8 mol% BaTiO3 (BNT-BT0.08) powder was prepared by an acetate-alkoxide sol-gel method. The evolution of the structure and microstructure of the precursor gel, heated at various temperatures as well as, the piezoelectric and ferroelectric properties of BNT-BT0.08 ceramics were studied. Nanopowder of BNT-BT0.08 with average particles size of 30 nm and, crystallized on the perovskitic structure of (Bi0.5Na0.5)TiO3, were obtained from the precursor gel by heating at 600 degrees C, 3 h in air. The ceramics of composition 0.92(Bi0.5Na10.5)TiO3-0.08BaTiO(3), manufactured from the as-prepared nanostructured powder, present good dielectric properties (epsilon(r,max) = 4000-4500, tan delta = 0.02-0.03) and high mechanical quality factor (Q(m) similar to 500). (C) 2009 Elsevier B.V. All rights reserved.

Ba(Mg1/3Ta2/3)O-3 (BMT) ceramic is a dielectric material possessing an extremely high Qxf product value (up to 400 THz) at microwave frequencies. This makes it suitable for applications as a dielectric resonator for wireless communications. BMT samples, prepared by solid-state reaction and doped with Nb5+, V5+ or Ga3+, were employed for compositional, structural morphological characterization. In the present study, we report on the influence of dopants (type and quantity) and sintering temperature on the dielectric properties. It was found that the quality factor is maximum when Nb5+ is used as dopant.

Maltol functionalized magnetite nanoparticles were synthesized by in situ decomposition of the precursor - polynuclear coordination compounds containing maltol as a ligand. X-ray diffraction, Mossbauer spectroscopy, Fourier transform infrared spectroscopy were used to characterize the nanoparticles system. The magnetic properties were measured by means of a superconducting quantum interference device. The particle size of the magnetite nanoparticles was estimated to be about 8 nm. At room temperature the magnetite nanoparticles were proved to be superparamagnetic with saturated magnetization of 67.29 emu/g and blocking temperature of about 175 K.

Gold layers were deposited at oblique incidence onto glass plates. A B30.2 Hochvakuum Bedampfungsanlage equipment was used in this aim. The deposition conditions were chosen in order to obtain nanostructured layers. Correlations were found among these conditions and the corresponding nomograms were then obtained. Examples of such depositions were given and the layers structure was characterized and additionally supported by observing the molecular alignment given in the liquid crystal cells obtained with these gold layers.

A simple and novel method for production of metal clusters as building blocks for nanoscale devices is presented. With this procedure, called the gas / cluster aggregation method, a wide range of clusters may be synthesised and, more important, these clusters may be subsequently modified and functionalized in-situ by adding atoms/molecules of different nature, on the surface of readily formed clusters. The cluster size is extremely well controlled by the vapour pressure of the picked-up species. Moreover, the method is versatile, since it allows multiple pick-up processes within the same rare gas cluster for producing, for example, core-shell nanoparticles with metal core and non-metallic shell or vice-versa, nano-onions, with different species successively attached to the surface of the initial picked-up cluster, and so on. Initial formation of Fe gas-stabilised clusters and core-shell nanoparticles with Fe core and Fe oxide shell, as well as their structure and morphology, are presented and discussed. The core-shell nanoparticles show incipient self-organization into hexagonal cluster superlattice. Structural, magnetic and Mossbauer spectroscopy investigations have been performed on the Fe cluster samples. The magnetic properties of supported Fe clusters show marked differences compared to the bulk. A small hysteresis is observed in the parallel applied field while in the perpendicular case, lack of saturation at the highest applied field is noticed. Such behaviour has been also observed in FeRh [1] and AgCo [2] bimetallic nanoparticles. This behaviour marks the occurrence of a strong planar magnetic anisotropy in the sample and may also be a consequence of increased surface spin disorder and finite size effects, which are typical for nanoparticles in the reported size range.

Samples of hematite were exposed to mechanochemical activation by high energy ball milling for 0-27 h. The milling-induced changes to the structural and magnetic properties of hematite were characterized by X-ray diffraction (XRD) and Mssbauer spectroscopy. The particle size was found to decrease from 80 to 16.5 nm after 8 h of ball milling time, followed by a small increase to 19.8 nm at the end of the milling period. An overall expansion of the crystalline lattice parameters a and c with the milling time was deduced. The magnetic hyperfine field decreased with the ball milling time, from 51.46 down to 50.68 T after 27 h of grinding. Magnetite and traces of iron were observed at the longest milling time employed. The recoilless fraction (f) was measured simultaneously using a dual Mssbauer absorber consisting of hematite and a stainless steel etalon. The f factor first decreased with the milling time due to occurrence of nanoparticles in the system, had a maximum at 12 h due to agglomerations of nanoparticles and exhibited a second maximum at 27 h, due to the appearance of magnetite in the system. More samples of hematite were subjected to magnetomechanical activation by magnetic ball milling for 52 and 134 h. A phase mixture of hematite and magnetite was observed.

The FePtNbB alloys are of interest as a new class of exchange spring magnets. In strictly defined compositional range and after proper conditions of annealing, they develop a microstructure made of small nanograins of hard and soft magnetic phases alternatively disposed and coupled through exchange interactions. Taking advantage of the high uniaxial aniosotropy of the tetragonal hard magnetic FePt phase and high saturation magnetization of the cubic soft magnetic FePt phases, an exchange coupled nanocomposite magnet can be derived. A compositional study of FePtNbB alloys is provided in order to understand the role of each additional element. The possibility of casting alloys where two or more magnetic phases can be obtained is discussed in terms of the eutectic point of the FePt phase diagram. Also, the formation and evolution of the magnetic phases is studied by differential scanning calorimetry (DSC) and detailed analysis of these DSC scans is provided. Activation energy determined from DSC scans provides essential informations about crystallization and disorder-order phase transformation in these alloys.

Mixed oxides nanocomposites of the type xCr(2)O(3)-(1-x)alpha-Fe2O3 (x = 0.0-1.0) were synthesized using hydrothermal technique and characterized by X-ray diffraction (XRD) and Mossbauer spectroscopy. The same characterization methods were applied to a set of samples annealed at 600 degrees C for 2 h. High chromium content correlated with occurrence of amorphization effects and onset of superparamagnetism in the as-obtained samples. The structure and properties of the thermally annealed samples, however, are dominated by the equilibrium of two phases, Cr:Fe2O3 and Fe:Cr2O3. The final (x = 1.0) particle size of the nanocomposite is close to 19 nm.