National Institute Of Materials Physics - Romania

Publications

5840 articles found

3851. Sintering distorsion produced by differences in green density and sample shape of PZT compacted powders

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

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

A study was made to determine the effect of sample shape, compacting pressure and green density gradients on the final shape and density of sintered bodies. Experiments were carried out on a PZT type powder, pressed with a large range of shapes from long cylinders up to thin discs, at pressures ranging between 40 and 180 MPa. Important shape distorsion were found for both long cylinders and thin discs but surprisingly the final density was not essentially changed even if the green compacted density showed important changes within the samples. Differences in shrinkage of diameter and thickness brought about by sintering for samples with different shapes were found.

3852. Mossbauer investigation of static-disorder crystalline media. V. Hyperfine fields' dispersion in static-disordered crystalline media of tetragonal and trigonal iron germanates

Authors: Constantinescu, S

Published: 2007, ROMANIAN REPORTS IN PHYSICS, 59, 43, DOI:

The refined Fe-57 Mossbauer spectra of some static-disordered crystalline media (with melilite and Ca-gallate structure) evidenced observable electric and magnetic crystal field dispersions [1-4]. The data of the crystalline hyperfine fields and their dispersion parameters were calculated using the modeling procedure given in [5]. The obtained values of the magnetic and quadrupole splitting parameters compared with the experimental data showed the possibility to predict the dispersion of the crystal fields.

3853. Basic principles of Mossbauer spectroscopy and applications

Authors: Filoti, G

Published: 2007, NMR-MRI, mu-SR and Mossbauer Spectroscopies in Molecular Magnets, 247, DOI: 10.1007/978-88-470-0532-7_9

3854. Structural and dielectric investigations of donor-acceptor substituted PZT ceramics

Authors: Dimitriu, E; Iuga, A; Ramer, R; Sandu, I; Cernea, M

Published: 2007, FERROELECTRICS, 353, 582, DOI: 10.1080/00150190701368091

Scanning electron microscopy (SEM) and energy dispersive X-ray measurements reveal inhomogeneities in the distribution of elements in W-, Li- doped PZT materials with the composition PbZr0.51 Ti0.49-2.5x W1.5xLixO3 (x = 0.03 and 0.05). Increasing the tungsten concentration leads to an increase of inhomegenities number in the PZT matrix. The high sintering temperature and Li+ concentration contribute to the vitreous aspect Of the materials. X-ray diffraction patterns revealed the Presence of both rhombohedral and tetragonal phases in the two materials. Considering the materials as composites with a 0-3 connectivity pattern, a mathematical approach is proposed. This was used to calculate the contribution of the agglomerations to the experimental dielectric constant.

3855. Dynamics studies of condensed matter using rayleigh scattering of mossbauer radiation

Authors: Bibicu, I; Enescu, SE

Published: 2007, ROMANIAN JOURNAL OF PHYSICS, 52, 118, DOI:

The Rayleigh scattering of Mossbauer radiation (RSMR) is a well-established and successful method for dynamics and structural investigations of ordered and disordered systems. The recoilless emission and absorption of low-energy gamma rays, combined with the high selectivity of the nuclear resonance absorption phenomenon, permits an energy resolution of the order of 10(-8) eV for the 14.4 keV transition of Fe-57. The results of our studies by RSMR on pyrolytic graphite (C) and rubidium tetrachlorozincate (Rb(2)nCl(4)) are given. The contribution of the coherent inelastic scattering to the total intensity in C(002) is described like a consequence of the coupling motions of C atoms in the hexagonal plan. The normal-incommensurate phase transition in Rb2ZnCl4 is discussed in connection with the photon-phonon interaction.

3856. Organic thin film transistors with HfO2 high-k gate dielectric grown by anodic oxidation or deposited by sol-gel

Authors: Tardy, J; Erouej, M; Deman, AL; Gagnalre, A; Teodorescu, V; Blanchin, MG; Canut, B; Barau, A; Zaharescu, M

Published: FEB-MAR 2007, MICROELECTRONICS RELIABILITY, 47, 377, DOI: 10.1016/j.microrel.2006.01.012

We report here on pentacene based organic field effect transistors (OFETs) with a high-k HfO2 gate oxide. HfO2 layers were prepared by two different methods: anodic oxidation and sol-gel. A comparison of the two processes on the electrical properties of OFETs is given. Ultra thin nanoporous (20 nm) sol-gel deposited oxide films were obtained following an annealing at 450 degrees C. They lead to high mobility and stable devices (mu = 0.12 cm(2)/V S). On the other hand, devices with anodic HfO2 revealed a little bit more leaky and show some hysteresis. Anodization, however, presents the advantage of being a fully room temperature process, compatible with plastic substrates. Stability and response to a bias stress are also reported. (c) 2006 Elsevier Ltd. All rights reserved.

3857. XPS, AES and ESR studies of Herastrau Lake sediments, Bucharest, Romania

Authors: Seletchi, ED; Negrila, C; Duliu, OG; Turcas, CV

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

X-Ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES) have been used to investigate the elemental composition, chemical and electronic state of elements that exist within the Herastrau Lake (Bucharest, Romania) sediments. XPS spectra were obtained by irradiating the sediment samples with an Al source of X-rays (1486.6 eV). A very broad peak at 165-190 eV corresponds to sulfur oxides, sulfate and sulfite ions and sulfur hexafluoride. The measurements indicate metal oxides: (Al2O3, Fe2O3) at 528-531 eV, SiO2 at 533 eV, phosphates, nitrates at 531-533 eV, silicates at 532-533 eV, CaO, CaCO3 and CaS at 346-347 eV, CaSo(4) at 348 eV, Ca(NO3)(2) at 349 eV and slight traces of NH3. A very intense peak at 784 eV also appears due to CoSO4. The analysis of Electron Spin Resonance (ESR) spectra revealed an additional free radical peak in the center of Mn2+ sextet, at a g = 2.0038, attributed to SO3- species as well a very intense and broad signal due to Fe3+ ions.

3858. Microstructure and properties of barium titanate ceramics prepared by mechanochemical synthesis

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

Published: 2007, ROMANIAN JOURNAL OF INFORMATION SCIENCE AND TECHNOLOGY, 10, 345, DOI:

The new advanced procedure of mechanochemical synthesis was used to prepare barium titanate from barium and titanium oxides. The X-ray examination of the powders milled for different times showed the phase evolution during synthesis. The perovskite phase was initiated after 5 hours of milling and was completed after 50 hours. Sintered samples from these nanopowders show different dielectric properties depending on their morphostructure. Thus for samples with an average grain size of 2 mu m we obtained the highest dielectric constant of 5 800 at room temperature. A sharp maximum of the dielectric constant with values of about 16 000 was recorded at the Curie temperature.

3859. Defected ground dual-mode resonators and filters

Authors: Banciu, MG; Militaru, N; Lojewski, G

Published: 2007, 2007 IEEE 18TH INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, VOLS 1-9, +, DOI:

A microstrip defected ground structure dual mode filter is presented. Several methods for coupling between the dual modes are investigated. Defected ground structure is used to enhance the external coupling and to introduce the necessary perturbation to the initially symmetrical structure. The proposed device is compact, requiring a surface area of about 6 times smaller than the area needed for a conventional patch dual mode resonator.

3860. Evaluation of the accuracy in determining the mechanical quality factor for piezoceramic resonators

Authors: Amarande, L; Miclea, C; Tanasoiu, C

Published: 2007, FERROELECTRICS, 350, 47, DOI: 10.1080/00150190701369776

Accuracies of three methods used to determine the mechanical qualily-factors of-piezoceramic resonators were evaluated and discussed-for the specific case of five materials with different mechanical quality factors (between 20 and 3000) and electromechanical coupling coefficients (between 2.5% and 60%). The mechanical quality factor Q(m) was calculatedfor both radial and thickness modes. The three methods are: the equivalent circuit, the band width and the iterative method. The last two methods proved to be very accurate for all materials (the error of Q(m) is less than 0.1%), but for low Q(m) materials the second method requires to redefine the involved frequencies. The first method is less accurate, especially for materials with low mechanical quality and electromechanical coupling factors or large difference between the mechanical quality factors of the resonance and antiresonance bands (the error of Q(m) is more than 10-20%).