National Institute Of Materials Physics - Romania

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849 articles found

541. Microwave properties of Ba(Zn1/3Ta2/3)O-3 dielectric resonators

Authors: Nedelcu, L; Toacsan, MI; Banciu, MG; Ioachim, A

Published: JAN 12 2011, JOURNAL OF ALLOYS AND COMPOUNDS, 509, 481, DOI: 10.1016/j.jallcom.2010.09.069

Ba(Zn1/3Ta2/3)O-3 (BZT) dielectric resonators were prepared by solid-state reaction. The starting materials were BaCO3, ZnO, and Ta2O5 powders with high purity. The double calcined BZT pellets were sintered in air at temperatures of 1575, 1600, 1625, and 1650 degrees C for 4 h. The X-ray diffraction data allowed the study of the unit cell distortion degree and the presence of the secondary phases. A long-range order with a 2:1 ratio of Ta and Zn cations on the octahedral positions of the perovskite structure was observed with the increase of the sintering temperature. The dielectric constant of BZT resonators measured around 6 GHz was between 26 and 28. High values of Q x f product (120 THz) were obtained for BZT resonators sintered at 1650 degrees C/4 h. The temperature coefficient of the resonance frequency exhibits positive values less than 6 ppm/degrees C. The achieved dielectric parameters recommend BZT dielectric resonators for microwave and millimeter wave applications. (C) 2010 Elsevier B.V. All rights reserved.

542. Structural investigations of Ge nanoparticles embedded in an amorphous SiO2 matrix

Authors: Stavarache, I; Lepadatu, AM; Gheorghe, NG; Costescu, RM; Stan, GE; Marcov, D; Slav, A; Iordache, G; Stoica, TF; Iancu, V; Teodorescu, VS; Teodorescu, CM; Ciurea, ML

Published: JAN 2011, JOURNAL OF NANOPARTICLE RESEARCH, 13, 232, DOI: 10.1007/s11051-010-0021-4

Transmission electron microscopy and X-ray photoelectron spectroscopy analyses are performed to investigate Ge nanoparticles embedded in an amorphous SiO2 matrix. GeSiO thin films are prepared by two methods, sol-gel and radio frequency magnetron sputtering. After the deposition, the sol-gel films are annealed in either N-2 (at 1 atm and 800 A degrees C) or H-2 (at 2 atm and 500 A degrees C), and the sputtered films in H-2 (at 2 atm and 500 A degrees C), to allow Ge segregation. Amorphous Ge-rich nanoparticles (3-7 nm size) are observed in sol-gel films. Crystalline Ge nanoparticles in the high pressure tetragonal phase (10-50 nm size) are identified in the sputtered films. The size of the nanoparticles increases with Ge concentration in the volume of the film. At the film surface, the Ge concentration is much larger that in the volume for both sol-gel and sputtered films. At the same time, at the film surface, only oxidized Ge is observed.

543. Band-gap correlations in Bi4Ge3O12 amorphous and glass-ceramic materials

Authors: Polosan, S; Galca, AC; Secu, M

Published: JAN 2011, SOLID STATE SCIENCES, 13, 53, DOI: 10.1016/j.solidstatesciences.2010.10.007

The Bi4Ge3O12 (BGO) glass materials were sintered from a mixture of oxides powders, rapidly heated and melted at 1323 K and poured on the graphite plates heated at different temperatures. Their optical properties are compared with BGO single crystals being strongly dependent by the experimental conditions, which influence the further stability of the samples. The dielectric functions of the samples reveal a clear difference between the two phases (amorphous and crystalline). The refractive index of the amorphous phase has lower values which indicate that the density of the material is diminishes. Also, a sign of disorder is seen in optical absorption (extinction coefficient). From the optical band gap determinations of those two phases, it is confirmed the disorder structure and red-shifts of the band gap value compared with crystalline phase. The absorption spectra are in good agreement with the ellipsometric measurements, regarding the transparency and the edge of the band gap. (C) 2010 Elsevier Masson SAS. All rights reserved.

544. Short-term repeatability of a rad-hard EPI diode applied in electron processing dosimetry

Authors: dos Santos, TC; Goncalves, JAC; Pintilie, I; Bueno, CC

Published: 2011, 2011 IEEE NUCLEAR SCIENCE SYMPOSIUM AND MEDICAL IMAGING CONFERENCE (NSS/MIC), 236, DOI:

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.

545. EFFECT OF TEMPERATURE ON THE MAGNETIC PROPERTIES OF CERAMIC MAGNETIC MATERIALS USED FOR TEMPERATURE TRANSDUCERS

Authors: Miclea, C; Amarande, L; Cioangher, M; Trupina, L; Miclea, CT; Plavitu, C; Spanulescu, I; Mihailescu, M

Published: 2011, 2011 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS 2011), 34TH EDITION, VOLS 1 AND 2, 272, DOI:

Three ceramic magnetic compositions within the CuZnTi ferrite system, having the Curie temperatures centered around 60 degrees C, 80 degrees C and 100 degrees C, respectively were investigated in order to determine the time-temperature stability of their main magnetic properties. Rates of changes of 33, 66 and 100 ppm/h of the maximum slopes of permeability were found for the samples aged at 60 degrees C, 80 degrees C and 100 degrees C, respectively. The samples aged at temperatures higher than 200 degrees C show a rather sudden decrease of the maximum slope of permeability, but no shift of the Curie temperature and the working point, corresponding to the temperature where the slope has the maximum value. The results are discussed in terms of the migration processes of the cations, especially Cu2+, from metastable positions on which they were frozen during the rapid cooling of the samples from the sintering temperature, to the more stable ones, namely the octahedral sites into the spinel lattice.

546. INFLUENCE OF ANNEALING TREATMENT OF NANO-HYDROXYAPATITE BIOCERAMICS ON THE VIBRATIONAL PROPERTIES

Authors: Ciobanu, CS; Andronescu, E; Stoicu, A; Florea, O; Le Coustumer, P; Galaup, S; Djouadi, A; Mevellec, JY; Musa, I; Massuyeau, F; Prodan, AM; Lafdi, K; Trusca, R; Pasuk, I; Predoi, D

Published: APR-JUN 2011, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 6, 624, DOI:

Nano-hydroxyapatite bio-ceramics were synthesized by sol-gel method. The gel was dried at 80 degrees C for 96 h. The dried gels were individually heated at a rate of 5 degrees C/min up to 600 degrees C, 800 degrees C, and 1000 degrees C. X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used for to characterize the composition, morphology and particle size of samples. At 800 degrees C a small amount of CaO (about 0.3 wt%) was detected in which increased after annealing at 1000 degrees C (about 1.1 wt%). The crystallites are elongated along the c crystallographic axis, but the size anisotropy decreases with increasing temperature above 800 degrees C. The size along the elongation axis increased from 43 nm at 80 degrees C to about 143 nm at 1000 degrees C, as determined by XRD, and from 120 to 280 nm, as measured by TEM. The functional groups were analyzed using Fourier transform infrared (FTIR) and Raman spectroscopies confirming the presence of various and PO43 and OH- bands in the samples. After calcination at 1000 degrees C the bands are more intense which indicates an increase in the cristallynity. The photoluminescence (PL) of HAp treated at various temperatures (80, 600, 800, 1000 degrees C) was also studied. hFOB 1.19 osteoblats cells were used to determine cell proliferation, viability and citotoxicity after interaction with the prepared bioceramics. To evaluate cell proliferation rate quantitative by the hFOB 1.19 cells on HAp samples were cultured to 4 days. Cellular morphology was investigated using FESEM to obtain qualitative information of osteoblast cells on HAp samples. The number of hFOB 1.19 cells on control HAp_80, HAp_600, HAp_800 and HAp_1000 was 400 +/- 30, 360 +/- 25, 350 +/- 21, 320 +/- 16 and 300 +/- 10 after 4 days. Our results proved that the HAp sintered at 1000 degrees C promoted osteoblast cell attachment and adhesion.

547. PREPARATION AND ELECTRICAL CHARACTERIZATION OF SiGe NANOSTRUCTURES

Authors: Stavarache, I; Lepadatu, AM; Pasuk, I; Teodorescu, VS; Ciurea, ML

Published: 2011, 2011 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS 2011), 34TH EDITION, VOLS 1 AND 2, 52, DOI:

This paper presents the preparation and investigation of structure and electrical properties of nanostructures consisting of Si1-xGex nanocrystals. Nanostructures were prepared by RF magnetron sputtering, followed by thermal annealing. X-ray diffraction, TEM, high resolution TEM and SAED measurements were performed. Current-voltage and current-temperature characteristics were taken. Nanostructures have different electrical behavior. Current-voltage curves are linear, while current-temperature curves are dependent on the annealing temperature. In films annealed at 650 degrees C, electrical transport is controlled by quantum confinement effect and localized states (current-temperature characteristics), while in films annealed at 900 degrees C it is controlled by tunneling of thermally activated carriers between neighboring nanocrystals.

548. Charge Transport in Ferroelectric Thin Films

Authors: Pintilie, L

Published: 2011, FERROELECTRICS - PHYSICAL EFFECTS, 134, DOI:

549. Shape Memory NiTi Alloys Obtained by Powder Metallurgy Route

Authors: Lucaci, M; Valeanu, M; Orban, RL; Tsakiris, V; Cirstea, DC; Leonat, L

Published: 2011, RESEARCHES IN POWDER METALLURGY, 672, +, DOI: 10.4028/www.scientific.net/MSF.672.99

The effect of Fe, respective Cu, additions as substitute for Ni in NiTi shape memory alloys (SMAs) on the delaying of its phase transition and narrowing hysteresis are well known, NiTi-Fe and NiTi-Cu SMAs having applications especially to the actuators that require such properties. These SMAs are currently produced by conventional melting methods, which are energo-intensive and impose very severe processing conditions to avoid contamination. The results of researches presented in this paper prove the possibility of these SMAs obtaining by powder metallurgy via reactive sintering - more advantageous from both technical and economic point of view. A beneficial effect on both sintering and homogeneity of the obtained SMAs proved to have a controlled mechanical alloying applied to powder mixture before compacting and sintering.

550. The Influence of Magnetron Sputtering Conditions on the Physical Properties of (001) Oriented Nanostructured ZnO Thin Films

Authors: Simon, S; Besleaga, C; Stan, GE; Ion, L; Arghir, I; Antohe, S

Published: 2011, PHYSICS CONFERENCE (TIM-10), 1387, DOI: 10.1063/1.3647074

Smooth, transparent and highly oriented nanostructured ZnO films were synthesized by RF-magnetron sputtering onto Si(100) substrates. A mild-pressed zinc oxide powder target was used for all depositions. The sputtering parameters were varied in order to obtain structures with good adherence and crystallinity. The depositions were carried out in inert argon atmosphere at four sputtering pressures (0.2 Pa, 0.25 Pa, 0.3 Pa and 0.45 Pa). ZnO films were deposited at 150 degrees C. The films were characterized from structural (XRD) and morphological (AFM) point of view. The influence of each sputtering parameter on the morphological and structural properties is discussed.