National Institute Of Materials Physics - Romania

Publications

5781 articles found

3961. Piezoelectric material for high efficiency ultrasonic siren

Authors: Dimitriu, E; Iuga, A

Published: 2006, ADVANCED MATERIALS FORUM III, PTS 1 AND 2, 514-516, 229, DOI: 10.4028/www.scientific.net/MSF.514-516.225

A PZT-type material, doped with niobium and lithium was prepared by the ceramic technique. The microstructure of the sintered material at 1280 degrees C was performed by scanning electron microscopy (SEM), transmission electron microscopy and by X-ray diffraction. Dielectric and piezoelectric properties were measured. The good planar properties of the material made it possible to obtain ceramic disks with a strong radial mode. Two such disks, glued together, with opposed polarisation constitute a bimorf element, which successfully converts the radial mode into a flexural one. At the center of the bimorf a conical acoustical impedance adapter is fixed in order to increase the frontal acoustical emission of the device. This ultrasonic device provides a broad band, high acoustical emission, and is suitable to work as a high efficiency ultrasonic siren. It can be used in intruder alarm devices, ultrasonic telemeters.

3962. Couplings control in the defected ground star-geometry dual-mode filter

Authors: Banciu, MG; Shen, S; Ramer, R; Militaru, N; Lojewski, G

Published: 2006, 2006 EUROPEAN MICROWAVE CONFERENCE, VOLS 1-4, +, DOI:

Investigations on coupling coefficients in a stargeometry filter with defected ground are presented in this paper. The device is compact, requiring a surface area of more than 6 times smaller than the area needed for a conventional patch dual mode resonator.

3963. Preparation of Mo-V-Te-Nb mixed oxides using the template route

Authors: Florea, M; Gaigneaux, EM; Parvulescu, VI

Published: 2006, , DOI: 10.1016/S0167-2991(06)80979-1

3964. A penetration depth study on Li2Pd3B and Li2Pt3B

Authors: Yuan, HQ; Vandervelde, D; Salamon, MB; Badica, P; Togano, K

Published: 2006, LOW TEMPERATURE PHYSICS, PTS A AND B, 850, +, DOI:

In this paper we present a penetration depth study on the newly discovered superconductors Li2Pd3B and Li2Pt3B. Surprisingly, the low-temperature penetration depth lambda(T) demonstrates distinct behavior in these two isostructural compounds. In Li2Pd3B, lambda(T) follows an exponential decay and can be nicely fitted by a two-gap BCS superconducting model with a small gap Delta(1)=3.2K and a large gap Delta(2)=11.5K. However, linear temperature dependence of lambda(T) is observed in Li2Pt3B below 03T(c), giving evidence of line nodes in the energy gap.

3965. Giant magnetoresistive coatings using thermionic vacuum are technology

Authors: Anghel, A; Luncu, CP; Mustata, I; Zaroschi, V; Lungu. AM; Barbu, I; Badulescu, M; Pompilian, O; Schinteie, G; Predoi, D; Kunkser, V; Filoti, G; Apetroaei, N

Published: 2006, CZECHOSLOVAK JOURNAL OF PHYSICS, 56, B23, DOI: 10.1007/s10582-006-0173-8

Giant magnetoresistive (GMR) coatings on silicon, glass and Kapton were prepared by simultaneous thermionic vacuum are (TVA) discharges in high vacuum conditions. The magnetic metal or alloy (Fe, Co, Ni, Permalloy) together with the noble non magnetic metal were deposited on substrates having different positions relative to the discharges. Local magnetic interactions and Fe-phase composition were obtained by Mossbauer spectroscopy whereas the magnetoresistance effects were measured by a dc method using a four-point configuration with perpendicular to plane magnetic fields up to 0.8 T. The surface morphology of the coatings was characterized by atomic force microscopy (AFM) in contact mode.

3966. Predictions and measurement of mass loading effects on quartz bulk acoustic wave resonators

Authors: Mateescu, I; Bran, C; Ballandras, S; Gachon, D

Published: 2006, PROCEEDINGS OF THE 2006 IEEE INTERNATIONAL FREQUENCY CONTROL SYMPOSIUM AND EXPOSITION, VOLS 1 AND 2, +, DOI:

The use of a variationnal perturbation method combined with finite element analysis is presented here to simulate the influence of mass-loading effects on the resonance frequency of bulk acoustic wave resonator. Computations are conducted on 2D and 3D and any shape of resonator can be considered. Predictions are compared to experimental data.

3967. Thermodynamic properties and spin dynamics of some micro and nanostructured magnetoresistive lanthanum manganites

Authors: Tanasescu, S; Marinescu, C; Maxim, F; Raita, O; Grecu, MN; Giurgiu, L

Published: 2006, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 26, 3010, DOI: 10.1016/j.jeurceramsoc.2006.02.020

The spin dynamics and thermodynamic properties of micro- and nanostructured lanthanum manganites La0.67Ca0.33Mn1-xMeO3 (Me = Al; x = 0-0.05) have been studied in order to evidence new features related to the effect of different compositional variables on the thermodynamic and magnetic behaviour. By electron paramagnetic resonance (EPR) spectroscopy, the influence of the grain size and the Mn substitution effects on the spin dynamics were investigated. A solid state electrochemical method was used to obtain the relative partial molar free energies, enthalpies and entropies of oxygen dissolution in the perovskite phase, as well as the equilibrium partial pressures of oxygen. The influence of the oxygen stoichiometry change on the thermodynamic properties has been investigated. The results were correlated with the average Mn valence values as determined by redox titration. In this paper an alternative method is proposed to estimate the contribution made by oxygen vacancies in balancing the local charge in CMR manganites. (c) 2006 Elsevier Ltd. All rights reserved.

3968. CW blue laser emission by second harmonic generation of 900nm oscillation of Nd-doped strontium and lanthanum aluminate (ASL)

Authors: Varona, C; Loiseau, P; Aka, G; Ferrand, B; Lupen, V

Published: 2006, SOLID STATE LASERS AND AMPLIFIERS II, 6190, DOI: 10.1117/12.662742

Nd-doped strontium and lanthanum (ASL) crystals Sr1-xLax-yNdyMgxAl12-xO19 (0.05 <= x <= 0.5; y = 0.05) were grown by Czochralski pulling technique. Up to 1.67W of 900mn rR output laser power for an absorbed power of 2.53W was obtained under Ti:sapphire pumping at 792nm. Intracavity second harmonic generation experiments led to 320mW of blue laser power at 450mn with a 10mm-long BiB3O6 nonlinear crystal. Other nonlinear crystals were also evaluated such as LBO.

3969. Scaling of conductivity through the critical temperature in Y0.54Pr0.46Ba2Cu3O7

Authors: Sandu, V; Katuwal, T; Taylor, BJ; Maple, MB; Almasan, CC

Published: 2006, LOW TEMPERATURE PHYSICS, PTS A AND B, 850, +, DOI:

In-plane conductivity sigma(ab) curves of Y0.54Pr0.46Ba2Cu3O7 single crystals, measured at constant temperature T in magnetic fields H tilted with an angle theta relative to the c-axis, were found to map onto a single curve in a sigma(ab) vs Hcos theta plot. This scaling occurs both below and above the critical temperature T-c, maintaining the same convexity, and is consistent with the dissipation caused by the motion of two-dimensional (2D) vortices. This indicates the presence of 2D vortices above T-c. A second scaling sigma(ab)(Hcos theta) takes place at higher T-c with an opposite convexity. This scaling is consistent with the dissipation of quasiparticies. There is a T range between these two regimes where no scaling is found. We attribute the absence of scaling in this intermediate regime to a 2D to 3D crossover in the vortex matter.

3970. Anisotropy of Na0.35CoO2 center dot 1.3H(2)O superconductor

Authors: Badica, P; Kondo, T; Togano, K; Yamada, K

Published: JAN-MAR 2006, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 67, 593, DOI: 10.1016/j.jpcs.2005.10.128

Magnetization M(H,T) and M(T,H) curves with magnetic field approximately parallel and perpendicular to the c-axis of Na0.35CoO2.1.3H(2)O superconducting crystals have been measured (T-c = 3.7 K). The shape of the M(H,T) loops resembles Bi-based high-T-c superconductors (HTS), but the superconducting anisotropy is below that of Bi-system; this parameter is as for HTS with middle or moderately high anisotropy. (c) 2006 Elsevier Ltd. All rights reserved.