Publications

A new noniterative method, for determining the dielectric, piezoelectric and elastic constants, in complex form, for piezoceramic materials, in the thickness extensional mode, was proposed. This method is very flexible, as it is based on the standard approach to determine the elastic stiffness, followed by the measurement of the impedance at two frequencies to calculate the dielectric and piezoelectric constants, by solving a system of two equations. The new method was tested on materials with various thickness coupling factors (k(t) = 4.5-60%) and mechanical quality factors (Q(m) = 20-1600), proving very good accuracy for all of them. The accuracy of standard method was also evaluated for the same materials. (C) 2014 Elsevier Ltd. All rights reserved.

Organic heterostructures were fabricated by matrix assisted pulsed laser evaporation (MAPLE) method using arylenevinylene oligomers based on triphenylamine (P78)/carbazole (P13) group and tris(8-hydroxyquinolinato)aluminum salt (Alq3). Optical properties of the organic multilayer structures were characterized by spectroscopic techniques: FTIR, UV-vis and photoluminescence (PL). A good transparency (over 60%) was remarked for the structures with two organic layers in the 550-800 nm range. Photoluminescence (PL) spectra proved that the emission characteristics of the materials have been preserved. I-V characteristics of (ITO/oligomer/Alq3/Al and ITO/Alq3/Al) heterostructures were symmetrically while rectifying properties of these heterostructures have not been observed. A comparison between the heterostructures made of layers with different thickness reveals that the higher current (8 x 10(-6) A at 1 V) was obtained for the ITO/P78/Alq3/Al heterostructure, which is characterized by a larger thickness of the double organic layer. AFM measurements revealed a similar topography while RMS values of the reported structures depend on the organic material. (C) 2013 Elsevier B.V. All rights reserved.

We report the continuous, single step synthesis of titania/iron-based magnetic nanocomposites in a single step using gas-phase laser pyrolysis technique by separately and simultaneously introducing the precursors (together with C2H4 sensitizer) in the reaction zone: Fe(CO)(5) on the central flow and, using air as carrier, TiCl4 on the annular coflow. The laser power and, for the last experiment, the injection geometry were modified in order to change the Fe/Ti ratio in the resulted nanopowders. Due to the specific geometry, the reaction zone (visible as a flame) have a reductive inner central zone surrounded by and oxidative environment, allowing the formation of the metallic-carbidic iron and/or iron-doped titania and iron oxide nanophases. The raw Fe-containing nanopowders have a ferromagnetic behavior, those synthesized at higher laser power and gas velocities show significant saturation magnetization M-s values (10-12 emu/g), whereas those obtained (with higher yield and carbon content) at lower laser power and gas velocities (using wider central nozzle cross-section) have a very weak magnetization (M-s similar to 0.05 emu/g) in spite of the higher ethylene carried Fe(CO)(5) flow. The powders were annealed in air at 400 degrees C show lower carbon content and, for those highly Fe-doped, the hematite phase formation. Preliminary tests using UV light confirm the photocatalytic action of the annealed nanopowders in salicylic acid degradation process in solution. (C) 2013 Elsevier B.V. All rights reserved.

This paper presents some studies about the bi-layer organic heterostructures realized with zinc phthalocyanine (ZnPc) as donor layer and 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA) as acceptor layer, on substrate of glass covered by Al doped ZnO (AZO) layer. These heterostructures have been prepared using laser techniques: pulsed laser deposition (PLD) in an atmosphere of oxygen for AZO films deposition and matrix assisted pulsed laser evaporation (MAPLE) for organic films deposition. The influence of the deposition conditions on the transmission of the organic films has been analysed. The effect of the oxygen plasma treatment, with duration of 5 min and 10 min, on the surface topography, structural and optical properties of AZO layers deposited by PLD and, as consequence, on the optical and electrical properties of the single layer (ZnPc) and bi-layer (ZnPc/NTCDA) organic heterostructure, deposited by MAPLE, was investigated. (C) 2014 Elsevier B.V. All rights reserved.

Vortex excitations and creep regimes in YBa2Cu3O7 (YBCO) films with nonsuperconducting nanorods (columnar defects) and/or nanoparticles in a low external magnetic field H oriented perpendicular to the film surface have been identified using standard DC magnetization relaxation measurements. It was found that by increasing the pinning energy dispersion through nanoparticle addition the relevant changes in the temperature T variation of the normalized magnetization relaxation rate S appear at relatively high temperatures (T similar to 65K for H = 2 kOe), owing to the inhibition of double vortex- kink formation. This indicates that the often observed S(T) maximum at low T (around 30 K) is not related to the excitation of double vortex kinks and super-kinks in specimens with columnar defects, as previously believed. The low-T S(T) maximum is present in the case of strongly pinned specimens without nanorods, as well, and depends on the film thickness, which definitely shows that it is caused by thermo-magnetic instabilities, as recently suggested. (C) 2014 Elsevier B.V.All rights reserved.

Multivalence Ce and Sn oxide doped materials are of critical importance in many renewable energy applications, especially in a porous form. Of special interest is the understanding of the basic properties of Ce-Sn-O nanoparticles and the effect of doping with different trivalent (Fe3+, Yb3+, Gd3+) elements, as well as developing Ce-Sn-O materials in the form of homogeneous and heterogeneous multilayers with unique properties at high temperature. We discuss various applications of nanosize metal-oxide sensors and energy conservation through improved energy efficiency such as renewable sources and fuel cells. In addition, ceria and ceria-based materials are studied for their electronic, magnetic, optical, and catalytic properties, which are important in applications such as gas sensors, heterogeneous catalysis, solid electrolyte fuel cells (SOFC), and UV-shielding application. Additionally, at the nanoscale, the surface area of metal oxide particles is dramatically increased, which not only increases oxygen exchange but also makes it easy for redox reactions.

In this work we have investigated the electrochemical processes by which Pt nanoparticles were included in (Bi,Sb)(2)Te-3 films and submicrometer wires. Solutions containing ions of Bi3+, HTeO2+ and Sb3+ as well as Pt nanoparticles or [PtCl6](2-) ions were used for this study. For comparison, a solution with the same composition in Bi3+, HTeO2+ and Sb3+ ions was used to study the electrodeposition process of (Bi,Sb)(2)Te-3 films and submicrometer wires. Linear and cyclic voltammetry was employed in experiments to find the influences of addition to electrodeposition bath of Pt nanoparticles or [PtCl6](2-) ions on deposition process of (Bi,Sb)(2)Te-3 film. Pt-(Bi,Sb)(2)Te-3 nanocomposites has been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectrometry (EDX) to determine structural, morphological and compositional properties. Two mechanisms for Pt nanoparticles embedding in (Bi,Sb)(2)Te-3 films and wires have been proposed. (c) 2014 Elsevier Ltd. All rights reserved.

xLi(2)O-(1 x)alpha-Fe2O3 (x=0.1, 0.3, 0.5, and 0.7) nanoparticle systems were successfully synthesized by mechanochemical activation of Li2O and alpha-Fe2O3 mixtures for 0-12 h of ball milling time. The study aims at exploring the formation of magnetic oxide semiconductors at the nanoscale, which is of crucial importance for catalysis, sensing and electrochemical applications. X-ray powder diffraction (XRD), Mossbauer spectroscopy and magnetic measurements were used to study the phase evolution of xLi(2)O-(1 x)alpha-Fe2O3 nanoparticle systems under the mechanochemical activation process. Rietveld refinement of the XRD patterns yielded the values of the particle size as function of composition and milling times and indicated the presence of Li-substituted hematite and tetra lithium iron oxide LiFeO2, along with the formation of multiple phases for large x values and long milling times. The Mossbauer studies showed that the spectrum of the mechanochemically activated composites evolved from a sextet for hematite to sextets and a doublet upon duration of the milling process with lithium oxide. Magnetic measurements recorded at 5 K to room temperature (RT) in an applied magnetic field of 50,000 Oe showed that the magnetization of the milled samples is larger at low temperatures than at RT and increases with decreasing particle size. Zero field cooling measurements made possible the determination of the blocking temperatures of the specimens as function of ball milling time and evidenced the occurrence of superparamagnetism in the studied samples. This result correlates well with the observed presence of a quadrupole-split doublet in the Mossbauer spectra. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Sintered bulks require new approaches for the control and improvement of their functional characteristics. Nanostructuring, synergy effects at interfaces in a composite, and technology specific features are essential in this regard. In this work, for a better understanding of challenges, complex relationships between materials and technology and different practical concepts such as "transferability", "composite within a composite", and "multilevel design", and "multifunctionality", a comparative analysis is proposed for very different nano structured materials such as La0.9Sr0.1Ga0.8Mg0.2O3-x x solid electrolyte, hard B4C-based materials, and doped MgB2 superconductors. Samples were obtained by reactive spark plasma sintering (SPS). SPS is reconfirmed as a powerful processing technique that generates high-density unique bulk materials impossible to fabricate by other methods. However, it is shown that SPS is not universal and its suitability should be carefully considered depending on materials and targeted applications. (C) 2014 The Japan Society of Applied Physics

The band bending at Cu/PZT(001) interfaces is investigated by X-ray photoelectron spectroscopy (XPS) for a PZT(001) layer which exhibits initial outwards ferroelectric polarization. Two competitive processes are identified: (a) formation of the Schottky barrier between the ferroelectric and unconnected Cu islands, and (b) coalescence of the Cu islands, realisation of an electrical contact to the ground of the system, inducing the apparent loss of the component of the ferroelectric polarization perpendicular to the sample surface, at least as it manifests in band bending. Three mechanisms are proposed to explain this loss of band bending when a full metal layer connected to ground is formed on the surface: (i) over-compensation of depolarization field in the sub-surface region, (ii) formation of domains with in-plane orientation of the polarization vector and (iii) loss of polarization in the near-surface layers of the ferroelectric due to electrons provided by the metal. These result in a non-monotonous variation of binding energies with the amount of Cu deposited. High resolution transmission electron microscopy and piezoresponse force microscopy confirmed these hypotheses. The XPS data allowed also to derive the surface PZT composition, its evolution with the deposition of copper and the formation of surface compounds.