National Institute Of Materials Physics - Romania

Publications

5840 articles found

3801. Dielectric properties of fine grains barium titanate ceramics prepared by mechanochemical synthesis

Authors: Miclea, C; Tanasoiu, C; Spanulescu, I; Miclea, CF; Gheorghiu, A; Amarande, L; Cioangher, M

Published: 2007, 2006 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, +, DOI:

Barium titanate was prepared by the advanced procedure of mechanochemical synthesis from barium and titanium oxides after 50 hours of milling. The X-ray examination of the milled powders showed the phase evolution during synthesis and the perovskite phase was initiated after 5 hours and was completed after 50 hours. Sintered samples from these nanopowders show different dielectric properties for fine and coarse grained ceramics. Samples with an average grain size of 2 mu m showed the highest dielectric constant of 5800 at room temperature. A sharp maximum of the dielectric constant with values of about 16000 was recorded at the Curie temperature.

3802. Preliminary study on detection of irradiated foodstuffs from the Romanian market

Authors: Cutrubinis, M; Chirita, D; Savu, D; Secu, CE; Mihai, R; Secu, M; Ponta, C

Published: AUG-SEP 2007, RADIATION PHYSICS AND CHEMISTRY, 76, 1454, DOI: 10.1016/j.radphyschem.2007.02.049

In order to fulfil the European task for market survey in food irradiation the first Romanian laboratory for detection of irradiated foodstuffs was established at IRASM Irradiation Centre. In this preliminary study, a wide range of Romanian food samples (spices, vegetables and meat) gamma irradiated at IRASM have been studied using different detection methods: (1) DNA comet assay, (2) thermoluminescence (TL) and (3) electron spin resonance (ESR) for foodstuffs containing bone or cellulose. The results suggest that there is no general available detection method and there is no perfect detection method. In conclusion, in order to carry out a correct identification of radiation treatment of a food sample it is recommended to use at least two standardised detection methods. (c) 2007 Elsevier Ltd. All rights reserved.

3803. Percolation phenomena in silicon - Based nanocrystalline systems

Authors: Lepadatu, AM; Rusnac, E; Stavarache, I

Published: 2007, CAS 2007 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, PROCEEDINGS, 578, DOI: 10.1109/SMICND.2007.4519789

The present paper analyzes the appearance of voltage percolation thresholds in the current - voltage characteristics measured on silicon-based nanocrystalline systems that present random space distribution of the nanocrystallites. This percolation phenomenon is explained on the basis of the probability of tunneling under applied bias and is related to the samples microstructure.

3804. Some contributions to the understanding of the puzzle of physical processes of degradation in irradiated silicon

Authors: Lazanu, S; Lazanu, I; Ciurea, ML

Published: 2007, CAS 2007 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, PROCEEDINGS, +, DOI:

In the present paper, we intend to bring some clarifications related to the role played by primary defects in long term degradation, to the dependence of degradation on the orientation of the wafer, as well as on the spatial distribution of the degradation produced by low energy particle irradiation.

3805. Optical and Mossbauer studies on YAG : Eu nanocrystals synthesized by a sol-gel method

Authors: Georgescu, S; Constantinescu, S; Chinie, AM; Stefan, AS; Toma, O; Bibicu, I

Published: 2007, ROMOPTO 2006: EIGHTH CONFERENCE ON OPTICS, 6785, DOI: 10.1117/12.755960

Optical and Mossbauer spectroscopy were used to put into evidence the morphological changes induced by the thermal treatments in the YAG:Eu nanocrystals synthesized by a sol-gel method. Both methods exhibit a drastic change of the monitored parameters (ratio of the areas of the electric and the magnetic dipole transitions - for optical spectroscopy and Mossbauer normalized area - for Mbssbauer spectroscopy) at the phase transition amorphous-crystalline, followed by a slow evolution of these parameters with the increase of the annealing temperature. This slow evolution is due to the increase in size of the nanocrystals.

3806. On the anomalous microwave power dependency of both non-resonant and CU2+ resonant microwave absorption in a YBa2CU3O7-delta type superconductor

Authors: Velter-Stefanescu, M; Duhu, OG

Published: 2007, SIX INTERNATIONAL CONFERENCE OF THE BALKAN PHYSICAL UNION, 899, 668, DOI:

A ceramic high temperature superconductor [HTS] of Y-Ba-Cu-O type has been investigated at 77 K by using a standard X-band Electron Paramagnetic Resonance (EPR) configuration. At very low microwave power (< 1 mW) the non-resonant or zero field signal (ZFS) was in phase with DPPH signal, pleading for an unambiguous absorption process, but it commutes to a typical superconductor signal (i.e. opposite to DPPH signal phase) with increasing the microwave power. At the same time, CU2+ signal appreciably changes its shape with increasing microwave power. These anomalous behaviors could be in part explained by a conventional SQUID response at microwave frequency by taking into account that the sample itself could be described by a collection of both Josephson and proximity junctions.

3807. Anomalous suppression of Bi2212 superconductivity in Bi1.8Pb0.4Sr2Ca2-xYxCu3-yZnyOw samples

Authors: Mihalache, PV; Aldica, G

Published: 2007, SIX INTERNATIONAL CONFERENCE OF THE BALKAN PHYSICAL UNION, 899, 628, DOI:

AC-susceptibility vs temperature measurements performed on (Bi,Pb)(2)Sr2Ca1-x YxCu2-yZnyOz phase present in sintered Bi1.8Pb0.4Sr2Ca2-x YxCu3-yZnyOw polycrystalline samples, 0 <= x <= 0.45 and y = 0 and 0.03. We report an anomalous suppression of superconductivity for x approximate to 0.3. For the first time in Bi-based cuprates, we report the presence of this anomaly not only in the Zn doped samples but also in the samples without Zn.

3808. Obtaining of Ni base intermetallic alloys by solidification control

Authors: Lucaci, M; Orban, RL; Lazarescu, M; Gavriliu, S; Lungu, M; Patroi, D

Published: 2007, MATERIALS AND TECHNOLOGIES, 23, +, DOI: 10.4028/www.scientific.net/AMR.23.283

Directional solidification techniques have been applied to produce Ni based intermetallic alloys with preferentially oriented columnar crystals extended along the complete length and parallel to the solidification direction. Enhanced ductility is expected from such alloys. In this paper we present the research results concerning the application of this technique to some complex Ni3Al-Fe-B alloys obtained from compacted mixtures of elemental powders. The corresponding master alloys have been obtained in a vacuum induction furnace by the known Exo-Melt process [1]. The directional solidification of these alloys was subsequently performed on cylindrical samples, at two solidification rates, 30 and 15 mm/h. The influence of the rate and composition used on the dimensional variations, densities, microstructure, constituent phases and lattice parameters, as well as on the surface chemical composition have been documented and are presented in the paper.

3809. Effect of the sintering temperature on the Ba(Zn1/3Ta2/3)O-3 dielectric properties

Authors: Ioachim, A; Toacsan, MI; Banciu, MG; Nedelcu, L; Dutu, CA; Feder, M; Plapcianu, C; Lifei, F; Nita, P

Published: 2007, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 27, 1122, DOI: 10.1016/j.jeurceramsoc.2006.05.023

Preparation of dielectric materials with optimal properties for wireless applications requires special thermal treatments due to the difficult control of the cationic ordering. The BZT samples prepared by solid-state reaction were sintered at temperatures in the range 1400-1600 degrees C for 4 h. For compositional, structural and morphological characterization, XRD, SEM and EDX were employed. The order-disorder transition of the BZT material was analyzed. With the increase of the sintering temperature, a long-range order with a 2:1 ratio of Ta and Zn cations on the octahedral positions of the perovskite structure was observed. The dielectric parameters were measured in the microwave range and were correlated with morphological and structural properties. In order to improve the microwave properties, annealing treatment at 1400 degrees C for 10 h was performed. Sintering temperatures greater than 1550 degrees C are required for undoped BZT compositions, in order to obtain low microwave loss (Qf > 100,000). (c) 2006 Elsevier Ltd. All rights reserved.

3810. A. comparative study of micro crystalline and nanocrystalline lead sulfide based PbS/SiO2/Si heterostructures

Authors: Stancu, V; Pentia, E; Goldenblum, A; Buda, M; Iordache, G; Botila, T

Published: 2007, ROMANIAN JOURNAL OF INFORMATION SCIENCE AND TECHNOLOGY, 10, 66, DOI:

The PbS micro-crystalline and nano-crystalline films were obtained using the Chemical Bath Deposition method. We investigated comparatively the structural, electrical and photoconductive properties of these films deposited on glass. PbS/SiO2/Si heterostructures made with nanocrystalline PbS layers present interesting peculiarities. Their C-V curves show hysterezis. In a field effect arrangement it is possible to control the photoconductive short and long wavelength ratio response. The heterostructure properties were explained by taking into account the interface charged traps.