Publications

The relaxation of the irreversible magnetization of optimally doped YBa2Cu3O7-delta (YBCO) films and YBa2Cu3O7-delta /PrBa2Cu3O7-delta (YBCO/PrBCO) superlattices in a magnetic field H oriented along the c axis was investigated over a large temperature T interval. The observed behavior is dominated by the presence of a crossover elastic vortex creep at low T-plastic creep at high T generated by the T-dependent current density J of the macroscopic currents induced in the specimen during experiments. Magnetization relaxation in the flux-creep annealing regime indicates the reduction of the creep crossover temperature with decreasing J, which suggests that in static conditions the disordered vortex phase at high H behaves like a plastically pinned vortex assembly, rather than an elastic vortex glass. The often reported scaling of the electric field E-transport current density J characteristics in agreement with an elastic vortex glass-vortex fluid transition seems to originate from the creep crossover generated by an increasing J.

The attractive properties of ceria, particularly the conductivity and chemical stability, have led to vast research efforts to investigate, characterize and develop such materials. One of the main applications of this ceramic is in the solid oxides fuel cells for intermediate temperatures IT-SOFC. The aim of this work is the preparation and characterization of cubic ceria nanopowders doped with 10 mol % yttria or Scandia. A thermal treatment (calcinations) was applied on the obtained nanopowders, which were consequently investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and selected aria electron diffraction (SAED).

The combination of two methods: Ag substrate decoration and introduction of BZO nano-inclusions has been used in a pulsed laser deposition (PLD) method to increase the critical density (J (c) ) of YBCO films. The films were deposited on single crystal SrTiO3 (STO) substrates decorated with various architecture of Ag nano-dots. We have studied the diameter and density of Ag nano-dots and their influence on J (c) of BZO-added YBCO films. We found that 15 laser pulses on the Ag target gives an optimum result in increasing J (c) in comparison with BZO-doped YBCO films of the same thickness in self-field and low applied magnetic fields. A higher number of laser pulses on the Ag target led to increasing critical current density in high applied magnetic fields only (above 2 T). We have studied films of the thickness from 0.4 mu m to 3.8 mu m and found that the highest J (c) at all applied fields investigated is achieved for a 1.2 mu m thick film. The transmission electron microscopy clearly shows BZO nano-rods that provide strong c-axis pinning centres in the films.

In this study, we report on the nanocrystalline powders of TiO2 and Fe-doped TiO2 (anatase and rutile phases) prepared by sol-gel method. The X-ray diffraction and Raman spectroscopy measurements indicated the presence of anatase or rutile phase in nanopowders. TEM micrographs showed 10 and 112 nm average particle sizes for anatase and rutile, respectively. Furthermore, their thermoluminescence properties were analyzed.

Magnetic shielding properties of MgB2 bulk samples synthesized by the SPS (Spark-Plasma-Sintering) technique were characterized in low applied magnetic fields at temperatures ranging from 20 to 37 K. The used growth technique allows one to produce this compound in different shapes and sizes required for shielding applications. In this framework, shielding magnetic-induction field profiles generated by MgB2-based shield components, shaped as planar thick disks, were measured by means of a suitable Hall probe in-plane array. The magnetic field distribution at different vertical distances above the sample was also obtained by a micrometric motion of the probe ensemble. Magnetic field profiles were then analyzed in the framework of the critical state model and the critical current density, J (c) , was evaluated. The J (c) magnitude indicates that the material under test is a good candidate for passive magnetic shield manufacturing up to temperatures close to the transition one.

The discovery of superconductivity in MgB2 and, more recently, in iron pnictides, revived the interest in two-component and other exotic superconductors, including in the field of vortex matter, as was shown recently by the discovery of "type 1.5" superconductivity. However, even some "older" exotic cuprates grown by high-pressure techniques showed interesting anomalies related to the interplay between Josephson and magnetic coupling and/or two-gap superconductivity. Here, we will present two such examples of exotic vortex matter: magnetically-coupled pancake-vortex molecules in super-multilayered cuprates, and vortex molecules composed of fractional flux quanta glued by an interband phase difference soliton, and will discuss the major differences between MgB2 and such multilayer cuprates in terms of the relative strength of the interband interaction and, respectively, in terms of the coherence and penetration lengths.

A range of nano techniques is explored in order to increase the critical current in pulsed laser deposited (PLD) superconducting YBa2Cu3O (x) (YBCO) thin films. The structural measurements are linked with magnetic and transport measurements of the films. The effectiveness of PLD techniques is analyzed from the point of view of the dimensionality of nanostructures formed prior to and during the film growth. It is shown that a combination of two-dimensional substrate decoration with nanoparticles before the film deposition and one-dimensional growth of external phase nanorods during the deposition offers a high critical current in magnetic field both along the c-axis and in the ab-plane of YBCO.

Yttria doped ceria reinforced with yttria doped alumina compound for IT-SOFC applications has been prepared by sol-gel method and sintered at 1300 degrees C, 1400 degrees C, 1500 degrees C. XRD, and SEM show the presence of a needle-like cerium-magnetoplumbite (CeAl11O17) phase in the compound; the oxygen deficient phase grows from the alumina phase by using ceria from the surrounding matrix and releasing oxygen ions As the sintering temperature is increased, the alumina phase is gradually transformed into CeAl11O17. Compared to the yttria doped ceria without reinforcement, the obtained compounds with ceria-magnetoplumbite show only a slight decrease of the Young elasticity modulus. However, the samples become brittle after backing in oxygen atmosphere (1000 degrees C, and 1500 degrees C).

The rad-hard EPI diode was characterized envisaging its application in on-line 1.5 MeV electron beam dosimetry in radiation processing. As expected from a current sensitivity loss (13.5%) to the accumulated dose up to 750 kGy, the EPI diode exhibited good short-term repeatability (CV = 1.9%) which is better than that required for CTA dosimeters, routinely applied in radiation processing. The dose-response curve of the EPI diode was fitted by a second order polynomial function for doses up to 775 kGy. In addition, some preliminary studies on the radiation damage effects induced in this diode using a Capacitance Deep Level Transient Fourier Spectroscopy system are presented. The results showed that up to almost 1.5 MGy only 3 defects (VO, V-2 and CiOi) can influence the carrier lifetime and current generated. Further radiation damage studies are under way.

The paper presents the experimental methods for determining lubricants wear degree and their durability, which led to the development of a global methodology for the lubricant behavior study. It is achieved a complex, service life, monitoring tool, based on four modules, input and output targets and the logical interconnections between elements.