National Institute Of Materials Physics - Romania

Publications

860 articles found

761. Effect of ytrium substitution on the structure and piezoelectric properties of lead titanate ceramics

Authors: Miclea, C; Amarande, L; Tanasoiu, C; Miclea, CF; Sandu, V; Gheorghiu, A

Published: 2004, 2004 International Semiconductor Conference, Vols 1and 2, Proceedings, 414, DOI:

Lead titanate (PT) is well known as a good piezoelectric material with high Curie temperature (similar to 490 degrees C) and low dielectric constant (similar to 200). Pure lead titanate cannot be sintered as ceramic bodies, due to its high crystalline anisotropy (c/a=1.064), but dense ceramic bodies can be obtained if small additions of other elements are used. In this regard we investigated the effect of Y addition on the structure and piezoelectric properties of PT ceramics, with general formula (Pb1-3x/2Yx)(Ti0.98Mn0.02)O-3, and x=0.04, 0.06, 0.08 and 0.10. Density and coupling factors were determined as a function of sintering temperatures, and doping level. Temperature dependence of the electromechanical behaviour was also investigated for temperatures as high as 500 degrees C. The Y modified PT ceramics have low dielectric constant (< 140), high Curie point (T-C > 450 degrees C), and large electromechanical anisotropy.

762. New planar compact dual mode filters for mobile communications

Authors: Banciu, MG; Lojewski, G; Ioachim, A; Nedelcu, L; Militaru, N; Shen, A; Ramer, R

Published: 2004, 2004 International Semiconductor Conference, Vols 1and 2, Proceedings, 140, DOI:

A new type of dual mode filter is proposed for mobile communications systems in 900 MHz frequency bandwidth such as GSM or GPRS. The planar filters were developed on a 0.635 mm substrate with a 10.8 dielectric constant. Several methods of modes coupling were investigated. Each dual mode resonator has a square-shape with the edge 20.5 mm and contributes with two poles to the filter response.

763. Electric and ferroelectric properties of Pb(Zr0.2Ti0.8)O-3 thin films deposited by pulsed laser deposition on single crystalline substrates

Authors: Pintilie, L; Lisca, M; Alexe, M

Published: 2004, 2004 International Semiconductor Conference, Vols 1and 2, Proceedings, 418, DOI:

Epitaxial Pb(Zr0.2Ti0.8)O-3 (PZT) thin films were grown on single crystalline Nb-doped SrTiO3 (STON) substrates by Pulsed Laser Deposition (PLD). The top electrode was SrRuO3. The investigated electric and ferroelectric properties have revealed a strong asymmetry of the two PZT-electrode interfaces. A qualitative explanation based on the possible existence of a n(+) - p junction at the STON-PZT interface is suggested.

764. Growth and properties of Pb(Zr0.92Ti0.08)O-3 thin films

Authors: Boerasu, I; Pintilie, L; Gomes, MJM; Pereira, M

Published: 2004, INTEGRATED FERROELECTRICS, 62, 87, DOI: 10.1080/10584580490460556

Lead zirconate-titanate (PZT) thin films with Zr/Ti ratio of 92/8 were deposited by sol-gel on Pt(111)-coated Si(100) and single crystal MgO(100) substrates. The films crystallize differently on the two type of substrates: in case of the films deposited on Pt the perovskite structure is established only after oxygen annealing, while for the films deposited on MgO annealing in air is enough. The films are polycrystalline with some preferred orientation that is substrate dependent. Average values of 2.1 muC/cm(2) and 78 kV/cm were obtained for remnant polarization and coercive field, respectively. The I-V characteristic at low to medium voltages is dominated by field enhanced Schottky emission, with Ln(J)similar to(V + V-bi)(1/4) dependence of the current density. A value of about 3.85 eV was estimated for the band-gap from optical measurements.

765. Dielectric ceramics based on the ZrO2-SnO2-TiO2 ternary system for microwave and milimeter wave applications

Authors: Ioachim, A; Toacsan, MI; Banciu, MG; Nedelcu, L; Ghetu, D; Stoica, G; Annino, G; Cassetari, M; Martinelli, M

Published: 2004, 2004 International Semiconductor Conference, Vols 1and 2, Proceedings, 426, DOI:

The paper describes the investigations of (Zr0.8Sn0.2)TiO4 compounds prepared by solid-state reaction techniques. The effect of La2O3, ZnO and NiO addition on microwave dielectric properties was investigated. The samples were sintered at temperatures T-s = 1280 divided by 1400 degrees C The inaterials exhibit a dielectric constant epsilon(r) similar to 36 and high values of the Q f productfroin 30,000 to 55,000 at microwave frequencies. The measured temperature coefficient of the resonance frequency tau(f) takes values in the range (-2 divided by+4) ppm/degrees C.

766. Synthesis and piezoelectric properties of nanocrystalline PZT-based ceramics prepared by high energy ball milling process

Authors: Miclea, C; Tanasoiu, C; Gheorghiu, A; Miclea, CF; Tanasoiu, V

Published: AUG-SEP 2004, JOURNAL OF MATERIALS SCIENCE, 39, 5434, DOI: 10.1023/B:JMSC.0000039260.82430.f9

Nanocrystalline powders of a soft FeNbLi-doped PZT material have been prepared by a novel mechanochemical process consisting of mixing the stoichiometric oxides in a planetary ball mill for prolonged times up to 80 h. The constituent oxides were reacted in a tungsten carbide vial with balls of 5, 10 and 20 mm in diameter and a ball/powder ratio of 15/1. The chemical reaction between the component oxides was triggered after 20 h of energetic milling and was completed after 80 h. The XRD of the reacted nanopowder showed the well known perovskite structure. Compacted samples of this powder were sintered between 800-1300degreesC for 3 h and the main piezoelectric properties were determined. The density of the sintered samples reached nearly 99% of the theoretical density at 1100degreesC and showed good piezoelectric characteristics: planar coupling factor of 0.66, dielectric displacement constant d(33) of 550 pm/V, mechanical quality factor of 85, and relative dielectric constant of 3800. The possible mechanisms for solid state reaction of mechanically activated nanopowders such as local heating and pressure at collision as well as defects diffusion are discussed. (C) 2004 Kluwer Academic Publishers.

767. Structural, electrical, and photoelectrical properties of CdxPb1-xS thin films prepared by chemical bath deposition

Authors: Pentia, E; Draghici, V; Sarau, G; Mereu, B; Pintilie, L; Sava, F; Popescu, M

Published: 2004, JOURNAL OF THE ELECTROCHEMICAL SOCIETY, 151, G733, DOI: 10.1149/1.1800673

CdxPb1-xS (0 less than or equal to x less than or equal to 1) thin films were prepared on glass substrates using the chemical bath deposition method. The structural, electrical, and photoelectrical properties of the films were investigated, and all were dependent on the x value. For x > 0.5 (high Cd content), the films show a poor crystallinity and weak photoconductivity. For x < 0.5 (high Pb content), the films exhibit a good crystallinity, with an average size of the crystallites of 100 nm, and good photoconductivity. The threshold voltage of photoconductivity is shifted to lower wavelengths with increasing Cd content. The experimental results point toward possible ternary deposition on some composition ranges (near pure PbS or CdS); whereas, for the rest, the deposited film is rather a mixture of phases [not CdxPb1-xS but (CdS)(x)(PbS)(1-x)]. (C) 2004 The Electrochemical Society.

768. Radiation hardness of silicon - a challenge for defect engineering

Authors: Stahl, J; Fretwurst, E; Lindstroem, G; Pintilie, I

Published: DEC 31 2003, PHYSICA B-CONDENSED MATTER, 340, 709, DOI: 10.1016/j.physb.2003.09.238

Thermally stimulated current measurements of silicon particle detectors have been performed for defect characterization after high levels of gamma- and proton-irradiation. Two defects closely correlated with the detector performance were monitored: a deep acceptor (1) and a bistable donor (BD). In oxygen rich silicon the deep acceptor is largely suppressed while the BD generation is strongly enhanced. The influence of the starting material (standard float zone (FZ), oxygen enriched FZ, Cz, epitaxial silicon) on the formation of these two defects is discussed. Identification of the I-defect with the V2O complex, and of BD with the thermal double donor TDD2 is suggested. (C) 2003 Elsevier B.V. All rights reserved.

769. Second-order generation of point defects in highly irradiated float zone silicon - annealing studies

Authors: Pintilie, I; Fretwurst, E; Kramberger, G; Lindstroem, G; Li, Z; Stahl, J

Published: DEC 31 2003, PHYSICA B-CONDENSED MATTER, 340, 582, DOI: 10.1016/j.physb.2003.09.131

Isothermal and isochronal annealing experiments have shown that the I defect (the main cause for the changes in silicon diodes characteristics after high levels of gamma-irradiation) is stable up to 325-350degreesC. Possible reactions, which can explain the behavior of different defects formed during the annealing experiments, are discussed. All the experimental results concerning the I center (second-order irradiation induced defect, formed most likely via VO center, suppressed in oxygen rich material, high thermal stability) make it the favorite for being associated with the V2O2 complex. (C) 2003 Elsevier B.V. All rights reserved.

770. Superior radiation tolerance of thin epitaxial silicon detectors

Authors: Kramberger, G; Contarato, D; Fretwurst, E; Honniger, F; Lindstrom, G; Pintilie, I; Roder, R; Schramm, A; Stahl, J

Published: DEC 11 2003, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 515, 670, DOI: 10.1016/j.nima.2003.07.021

For the LHC upgrade (fluences up to 10(16) p/cm(2)) epi-Si devices are shown to be a viable solution. No type inversion was measured up to 1.3 x 10(15) 24 GeV/c protons/cm(2) and the charge collection efficiency (CCE) remained close to 100%. For reactor neutrons CCE was measured to be 60% at 8 x 10(15) n/cm(2). Annealing measurements have shown that only moderate cooling during beam off periods would be necessary. As a tentative explanation for the superior quality of these devices, we assume that radiation-induced donor generation leads to compensation effects of deep acceptors. In the future, we will extend the experiments to fluences up to 10(16) p/cm(2) and use also different variants of the epi-Si material and device geometry. (C) 2003 Elsevier B.V. All rights reserved.