National Institute Of Materials Physics - Romania

Publications

5840 articles found

3861. Dielectric properties of (Ba,Sr)TiO3 thin films for applications in electronics

Authors: Ioachim, A; Toacsan, MI; Nedelcu, L; Banciu, MG; Dutu, CA; Buda, M; Sava, F; Popescu, M; Scarisoreanu, N; Dinescu, M

Published: 2007, ROMANIAN JOURNAL OF INFORMATION SCIENCE AND TECHNOLOGY, 10, 354, DOI:

Barium strontium titanate (BST) bulk ceramic was used as target for PLD thin film deposition. In order to avoid stoichiometry modification during the deposition, a more reactive oxidant ambient in the chamber was produced by rising a radiofrequency discharge 13.56 MHz, 150 W. Thin films of stoichiometric BST was deposited on alumina substrate with the thickness between 400 and 500 nm heated at 650 degrees C. An aditional anealing was made at 800 degrees C for 6 hours. XRD and SEM were used for sample characterization. Capacity measurements at 100 kHz were performed versus temperature.

3862. Mesoseopic ordering in the 0.9 Pb(Mg1/3Nb2/3)O-3-0.1 PbTiO3 relaxor ferroelectric: a HRTEM study

Authors: Nistor, LC; Ghica, C; Van Tendeloo, G

Published: 2007, PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 4, NO 3, 4, +, DOI: 10.1002/pssc.200673753

We report a microstructural and compositional study of a 90% Pb(Mg1/3Nb2/3)O-3 - 10% PbTiO3 ceramic sample. High resolution transmission electron microscopy (HRTEM) revealed the presence of compositional ordered nano-domains (1 - 4 mn), observable in two specific orientations, [0 (1) over bar 1] and [1 1 (2) over bar]. However, the visibility and the ordering degree of the nano-domains on the HRTEM images are not at all obvious. Fourier filtering of the images clearly revealed the ordered domains. Antiphase boundaries lying in the (111) planes separate them, while (100) and (111) facets separate the ordered domains from the disordered matrix. Their shape is plate-like, not uniformly spread in the disordered matrix. Their average size varies in different regions of the sample, most probably due to a non-uniform distribution of Ti, as observed by energy dispersive X-ray spectroscopy. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

3863. Effect of lead content on the structure and piezoelectric properties of hard type lead titanate-zirconate ceramics

Authors: Miclea, C; Tanasoiu, C; Miclea, CF; Amarande, L; Gheorghiu, A; Spanulescu, I; Plavitu, C; Miclea, CT; Cioangher, MC; Trupina, L; Iuga, A

Published: 2007, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 27, 4059, DOI: 10.1016/J.jeurceramsoc.2007.02.094

In the present investigation we studied the effect of lead content on a hard type ceramics starting from lack to excess PbO. Specimens of Pb-x(Mn0.017Sb0.033Zr0.48Ti0.47)O-3 with 0.96 <= x <= 1.06 were prepared by conventional oxide mixing technique and sintered at temperatures between 1280 and 1350 degrees C. In samples with lower Ph concentration the pyrochlore phase appeared, while in those with higher Pb an excess of PbO phase was detected. These phases proved detrimental for the properties of sintered ceramics. The highest values of piezoelectric properties were observed only for samples with an excess lead of about 2% sintered at 1340 degrees C, indicating that it represents the optimum amount of PbO. For such samples, the density p was 7.77 g/cm (3). the remnant polarization P, was 37 mu C/cm(3) the planar coupling coefficient k(P) was 0.57 and the charge constant d(33) was 340 C-P/N. (c) 2007 Elsevier Ltd. All rights reserved.

3864. Phase instability in ZrO2-TiB2 composites

Authors: Sarbu, C; Vleugels, J; Van der Biest, O

Published: 2007, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 27, 2208, DOI: 10.1016/j.jeurceramsoc.2006.07.014

2.5 mol% Y2O3-stabilised ZrO2 composites with 30 vol.% TiB2 particles, hot pressed in vacuum at 1450 degrees C, were investigated by means of quantitative electron energy loss spectroscopy (EELS) with a nanobeam analytical field emission gun transmission electron microscope (FEG-TEM). The experimental results revealed that B is diffusing out of the titanium boride grains, forming textured polycrystalline BN agglomerates leaving behind non-stoichiometric TiB2-x single crystal grains. The formation of BN was calculated to be thermodynamically favourable under the actual hot pressing conditions. Boron was also detected in the amorphous intergranular phase, together with Y, Si, O, Al, but not in the ZrO2 grains. Ti was only detected in the amorphous material in-between the TiB2-x grains and the micro-textured BN grains, but not in the zirconia grains nor in the intergranular amorphous phase in between. There are indications that Ti forms facetted carbide precipitates inside the TiB2-x grains. Zr was not detected in the titanium boride grains, nor in the intergranular amorphous phase in-between the zirconia grains. (c) 2006 Elsevier Ltd. All rights reserved.

3865. High K dielectric resonator antenna

Authors: Ioan, N; Andrei, I; Irina, T; Ionut, R; Gabriel, B

Published: 2007, TOPICS IN APPLIED ELECTROMAGNETICS AND COMMUNICATIONS: PROCEEDINGS OF THE 5TH WSEAS INTERNATIONAL CO, DOI:

The microwaves are used for both civilian and military applications for communication and detection. Due to the emerging applications and the need for more bandwidth as well as for high speed, there is a strong competition for ultra high frequencies devices. As it is know the size of different kind of microwave components is in a certain relation with the wavelength divided by root square of the dielectric permittivity. So the size of microwave component can be decreased by increasing the dielectric permittivity. Dielectric materials based on TiO2 are recommended for applications in electromagnetism and optics due to their nonlinear properties, to high value of the dielectric permittivity and their temperature behavior. The paper describes very shortly the technology applied to manufacture high dielectric permittivity materials based on TiO2 and a dielectric resonator antenna manufactured with these materials. The experimental data measured for dielectric antenna are presented.

3866. Tin nanoclusters obtained in potassium chloride by thermal annealing

Authors: Apostol, E; Enculescu, M; Polosan, S; Vasile, E; Topa, V

Published: 2007, PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 4, NO 3, 4, +, DOI: 10.1002/pssc.200673734

Tin nanoclusters were obtained in potassium chloride crystals following the electrolytic coloration of KCl:Sn2+ and KCl:Sn2++Ca2+ crystals and thermal annealing at various temperatures and times. Electrolytic coloration of KCl:Sn2+ crystals produces electronic centers inside of samples, presumably negative metal ions of tin. Optical absorption measurements were performed on as grown sample, colored and thermal annealed samples. The behavior of the samples with Sn colloids was compared with theoretical predictions according to Mie's theory. Tin nanoclusters in KCl exhibit an absorption band with a peak at 215 nm. The structure of the nanoclusters was studied by optical absorption and transmission electron microscopy means. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

3867. Comparative characterization of PbS macro- and nano-crystalline photoresistive detectors

Authors: Iordache, G; Buda, M; Stancu, V; Botila, T

Published: 2007, CAS 2007 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, PROCEEDINGS, 202, DOI: 10.1109/SMICND.2007.4519680

A comparative study of photodetector performance for nano- and micro-crystalline PbS thin layers is presented Both types of PbS films were obtained using the Chemical Bath Deposition method. To prepare nano-crystalline thin films we used a short reaction time with no doping Bi added At low levels of irradiance (0.1 mW/cm(2)) and room temperature (RT), the macro-crystalline PbS outperforms its nano-crystalline counterpart, by a factor of 6 for the value of Delta R/R-dark. However the nano-crystalline photodetectors show significantly lower optical quenching for large values of irradiance (approximate to 500 mW/cm(2)) at RT and better Delta R/R-dark performance at lower temperature, with an optimum temperature Of 150 K. The low frequency noise behavior is a superposition of 1/f flicker noise at low frequency and generation-recombination and thermal noise at higher frequency. The proportionaliiy factor between the 1/f noise and the DC dark current for the series resistor is 1.5 times larger for the nano-crystalline photodetector at room temperature.

3868. Dielectric resonators for microwave and millimeter wave applications

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

Published: 2007, CAS 2007 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, PROCEEDINGS, 278, DOI: 10.1109/SMICND.2007.4519700

Three types of materials for dielectric resonators are presented in this paper. The Pb-BNT materials show the highest dielectric constant (similar to 85). A very small controllable temperature coefficient if in the range (-2 divided by +4) ppm/degrees C can be achieved by using dielectric resonators Mg-(Zr0.8Sn0.2)TiO4. On the other hand, the resonators made of Ba(Zn1/3Ta2/3)O-3 exhibit the highest values for the Qxf product, ranging from 50000 to 130000 GHz, which make them attractive for millimetre wave applications.

3869. Structural (ME, XRD, NGR, ESR) investigations on some sulphides from costesti, valea lui stan and jidostita gold ores (Southern Carpathians, Romania)

Authors: Udubasa, SS; Constantinescu, S; Grecu, MN; Popescu-Pogrion, N; Udubasa, G; Popescu, GC; Tolea, F; Popescu, IV

Published: 2007, ROMANIAN JOURNAL OF PHYSICS, 52, 104, DOI:

An extensive investigation of the gold ores in the South Carpathians (Costesti, Valea lui Stan si Jidostita) has performed, using different chemical and physics experimental techniques. The used structural techniques have been the electron microscopy, X-ray diffraction, Mossbauer effect and electron spin resonance. The investigation of the representative samples by the structural techniques relieved new minerals in the gold ores, the presence of the "coral like" aggregates of nanometric gold solid bubbles.

3870. Angle-resolved photoemission study of the cobalt oxide superconductor NaxCoO2 center dot yH(2)O: Observation of the Fermi surface

Authors: Shimojima, T; Ishizaka, K; Tsuda, S; Kiss, T; Yokoya, T; Chainani, A; Shin, S; Badica, P; Yamada, K; Togano, K

Published: DEC 31 2006, PHYSICAL REVIEW LETTERS, 97, DOI: 10.1103/PhysRevLett.97.267003

The cobalt oxide superconductor NaxCoO2 center dot yH(2)O is studied by angle-resolved photoemission spectroscopy. We report the Fermi surface (FS) topology and electronic structure near the Fermi level (E-F) in the normal state of NaxCoO2 center dot yH(2)O. Our result indicates the presence of the hexagonal FS centered at the Gamma point, while the small pocket FSs along Gamma-K direction are absent, similar to NaxCoO2. The top of the e(g)(') band, which is expected in band calculations to form the small pocket FSs, extends to within similar to 30 meV below E-F, closer to E-F than in NaxCoO2. We discuss its possible role in superconductivity, comparing with other experimental and theoretical results.