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Dărăşti-Ilfov, Romania

Craciun F.,CNR Institute for Complex Systems | Galassi C.,CNR Institute of Science and Technology for Ceramics | Birjega R.,NILPRP
Journal of Applied Physics | Year: 2012

Complex dielectric susceptibility was used to investigate the relaxor properties and the ferroelectric phase transitions in (Na1/2Bi 1/2)1 - xBaxTiO3 (0 ≤ x ≤ 0.08) ceramics. XRD was used to characterize the ground states of poled and unpoled samples. Dielectric susceptibility vs. temperature studies allowed to obtain the relaxor properties and to identify the electric field-induced phase transitions in the morphotropic phase boundary (MPB) compositions (0.06 < x < 0.08) and the spontaneous relaxor-ferroelectric phase transitions in the rhombohedral compositions (x < 0.06). The frequency dispersion of the dielectric maximum at Tm was observed for all compositions, although of decreased extension for lower x. The relaxor properties have been analysed with Vogel-Fulcher law. The activation energy and attempt frequency for the MPB compositions are similar to those of classical relaxors like Pb(Mg 1/3Nb2/3)O3, while for rhombohedral compositions, they are similar to relaxor ferroelectrics with spontaneous relaxor-ferroelectric phase transitions, like Pb(Sc1/2Nb 1/2)O3. A relationship has been found between the relaxor dispersion degree and the hysteresis of the ferroelectric transition. © 2012 American Institute of Physics. Source

Ionita I.,University of Bucharest | Zamfirescu M.,NILPRP
2011 International Workshop on Biophotonics, BIOPHOTONICS 2011 | Year: 2011

We report here bone tissue ablation experiments performed with femtosecond laser. We determined ablation threshold value of human mandible which is the hardest bone of the skull. © 2011 IEEE. Source

D'Amato R.,ENEA | Falconieri M.,ENEA | Gagliardi S.,ENEA | Popovici E.,NILPRP | And 3 more authors.
Journal of Analytical and Applied Pyrolysis | Year: 2013

Nanoparticles are the building blocks of many approaches for realizing nanostructured materials and devices. The technique of CO2 laser pyrolysis of gas- or vapour-phase precursors for the synthesis of nanoparticles has proven to be a very flexible and versatile technique which permits to cope with several challenges in different sectors of nanotechnology. Different kinds of pyrolytic nanopowders with average size in the range 5-60 nm and a narrow size distribution, have been produced and tested for the fabrication of structural materials and/or for functional applications in various fields. Here we report new results on the synthesis of SiC, TiO2 and SiO 2 nanoparticles for energetic applications and cultural heritage preservation. © 2013 Elsevier B.V. All rights reserved. Source

Cachoncinlle C.,University of Orleans | Hebert C.,CNRS Nanosciences Institute of Paris | Perriere J.,CNRS Nanosciences Institute of Paris | Nistor M.,NILPRP | And 2 more authors.
Applied Surface Science | Year: 2015

Low-dimensional semiconductor structures on nanometer scale are of great interest because of their strong potential applications in nanotechnologies. We report here optical and structural properties on UV lasing in ZnO thin films. The ZnO films, 110 nm thick, were prepared using pulsed-laser deposition on c-cut sapphire substrates at 500 °C under 10-2 oxygen pressure. The ZnO films are nearly stoichiometric, dense and display the wurtzite phase. The films are highly textured along the ZnO c-axis and are constituted of nanocrystallites. According to Hall measurements these films are conductive (0.11 Ω cm). Photoluminescence measurements reveals a so-called random lasing in the range 390 to 410 nm, when illuminating at 355 nm with a tripled frequency pulsed Nd-YAG laser. Such random lasing is obtained at rather low optical pumping, 45 kW cm-2, a value lower than those classically reported for pulsed-laser deposition thin films. © 2014 Elsevier B.V. All rights reserved. Source

Scarisoreanu N.D.,NILPRP | Craciun F.,CNR Institute for Complex Systems | Chis A.,NILPRP | Birjega R.,NILPRP | And 3 more authors.
Applied Physics A: Materials Science and Processing | Year: 2010

Na0.5Bi0.5TiO3-BaTiO3 (NBT-BT) thin films grown by pulsed laser deposition have been investigated by X-ray diffraction, scanning electron microscopy, and dielectric spectroscopy in order to clarify the role of substrate temperature on crystalline structure, grain morphology, and dielectric properties. We have shown that the structural and dielectric properties of NBT-BT thin films with composition at morphotropic phase boundary (6% BT) critically depend on the substrate temperature: small variations of this parameter induce structural changes, shifting the morphotropic phase boundary toward tetragonal or rhombohedral side. Higher deposition temperature (1000 K) favor the formation of rhombohedral phase, films deposited at 923 K and 973 K have tetragonal symmetry at room temperature. Grains morphology depends also on the deposition temperature. Atomic force micrographs show grains with square or rectangular shape in a compact structure for films grown at lower temperatures, while grains with triangular shape in a porous structure are observed for films grown at 1000 K. Dielectric spectroscopy measurements evidenced the phase transition between ferroelectric and antiferroelectric phase at 370 K. Films grown at 1000 K shown low electrical resistivity due to their porous structure. High dielectric constant values (about 800 at room temperature and 2700 at 570 K) have been obtained for films grown at temperatures up to 973 K. © 2010 Springer-Verlag. Source

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