National Institute Of Materials Physics - Romania

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873 articles found

701. Barium strontium titanate-based perovskite materials for microwave applications

Authors: Ioachim, A; Toacsan, MI; Banciu, MG; Nedelcu, L; Vasiliu, F; Alexandru, HV; Berbecaru, C; Stoica, G

Published: 2007, PROGRESS IN SOLID STATE CHEMISTRY, 35, 520, DOI: 10.1016/j.progsolidstchem.2007.01.017

Ba1-xSrxTiO3 solid solutions were prepared by solid-state reaction from raw materials. Four compositions with x = 0.25, 0.50, 0.75 and 0.90 have been investigated. The perovskite type and polycrystalline structure of the BST samples were revealed by X-ray diffraction data. The morphology, grain size distribution, porous structure and elemental composition of the sintered ceramics were analyzed by using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) microanalysis. The temperature dependence of permittivity and of dielectric loss tangent at low frequency (1 kHz) showed decrease of Curie temperature with increase of Sr content. Microwave measurements (1 GHz) showed substantial decrease of the dielectric constant from about 1600 to 200 and also of the losses from 12% to less than 2% with the Sr concentration increase from x = 0.25 to x = 0.90. Moreover, the addition of MgO and MnO2 1 wt.% each, improved sintering process and lowered the microwave losses up to 0.2%. (c) 2007 Elsevier Ltd. All rights reserved.

702. Dielectric properties of fine grains barium titanate ceramics prepared by mechanochemical synthesis

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

Published: 2007, 2006 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, +, DOI:

Barium titanate was prepared by the advanced procedure of mechanochemical synthesis from barium and titanium oxides after 50 hours of milling. The X-ray examination of the milled powders showed the phase evolution during synthesis and the perovskite phase was initiated after 5 hours and was completed after 50 hours. Sintered samples from these nanopowders show different dielectric properties for fine and coarse grained ceramics. Samples with an average grain size of 2 mu m showed the highest dielectric constant of 5800 at room temperature. A sharp maximum of the dielectric constant with values of about 16000 was recorded at the Curie temperature.

703. Effect of the sintering temperature on the Ba(Zn1/3Ta2/3)O-3 dielectric properties

Authors: Ioachim, A; Toacsan, MI; Banciu, MG; Nedelcu, L; Dutu, CA; Feder, M; Plapcianu, C; Lifei, F; Nita, P

Published: 2007, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 27, 1122, DOI: 10.1016/j.jeurceramsoc.2006.05.023

Preparation of dielectric materials with optimal properties for wireless applications requires special thermal treatments due to the difficult control of the cationic ordering. The BZT samples prepared by solid-state reaction were sintered at temperatures in the range 1400-1600 degrees C for 4 h. For compositional, structural and morphological characterization, XRD, SEM and EDX were employed. The order-disorder transition of the BZT material was analyzed. With the increase of the sintering temperature, a long-range order with a 2:1 ratio of Ta and Zn cations on the octahedral positions of the perovskite structure was observed. The dielectric parameters were measured in the microwave range and were correlated with morphological and structural properties. In order to improve the microwave properties, annealing treatment at 1400 degrees C for 10 h was performed. Sintering temperatures greater than 1550 degrees C are required for undoped BZT compositions, in order to obtain low microwave loss (Qf > 100,000). (c) 2006 Elsevier Ltd. All rights reserved.

704. A. comparative study of micro crystalline and nanocrystalline lead sulfide based PbS/SiO2/Si heterostructures

Authors: Stancu, V; Pentia, E; Goldenblum, A; Buda, M; Iordache, G; Botila, T

Published: 2007, ROMANIAN JOURNAL OF INFORMATION SCIENCE AND TECHNOLOGY, 10, 66, DOI:

The PbS micro-crystalline and nano-crystalline films were obtained using the Chemical Bath Deposition method. We investigated comparatively the structural, electrical and photoconductive properties of these films deposited on glass. PbS/SiO2/Si heterostructures made with nanocrystalline PbS layers present interesting peculiarities. Their C-V curves show hysterezis. In a field effect arrangement it is possible to control the photoconductive short and long wavelength ratio response. The heterostructure properties were explained by taking into account the interface charged traps.

705. Thermal treatments effects on microwave dielectric properties of Ba(Zn1/3Ta2/3)O-3 ceramics

Authors: Ioachim, A; Toacsan, MI; Nedelcu, L; Banciu, MG; Dutu, CA; Andronescu, E; Jinga, S

Published: 2007, ROMANIAN JOURNAL OF INFORMATION SCIENCE AND TECHNOLOGY, 10, 268, DOI:

Ba(Zn1/3Ta2/3)O-3 dielectric materials were prepared by solid state reaction. The samples were sintered at temperatures in the range 1 400 divided by 1 600 degrees C for 4 h. Morphostructural characterization was performed by using SEM and XRD. The dielectric properties were measured in the microwave range (6 divided by 7 GHz). An additional annealing at 1 400 degrees C for 10 hours was performed in order to improve the dielectric parameters. The best parameters were achieved for the samples sintered at 1 600 degrees C with additional thermal treatment.

706. Annealing effects on properties of Ba(Zn1/3Ta2/3)O-3 dielectric materials

Authors: Ioachim, A; Toacsan, MI; Banciu, MG; Nedelcu, L; Dutu, CA; Andronescu, E; Jinga, S

Published: 2007, 2006 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, +, DOI:

Ba(Zn1/3Ta2/3)O-3 dielectric materials were prepared by, solid state reaction. The samples were sintered at temperatures in the range 1400 divided by. 1600 degrees C for 4 h. Morphostructural characterization was performed by using SE l and XRD. The dielectric properties were measured in the microwave range (6 divided by 7 GHz). An additional annealing at 1400 degrees C for 10 hours was performed in order to improve the dielectric parameters. The best parameters were achieved for the samples sintered at 1600 degrees C with additional thermal treatment.

707. Ferroelectric ceramics based on the BaO-SrO-TiO2 ternary system for microwave applications

Authors: Ioachim, A; Ramer, R; Toacsan, MI; Banciu, MG; Nedelcu, L; Dutu, CA; Vasiliu, F; Alexandru, HV; Berbecaru, C; Stoica, G; Nita, P

Published: 2007, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 27, 1180, DOI: 10.1016/j.jeurceramsoc.2006.05.086

Ba1-xSrxTiO3 solid solutions with x = 0.25, 0.5, 0.75 and 0.9 were prepared by solid-state reaction from powder oxides with high purity. In order to improve the granular growth 1 wt.% MgO and 1 wt.% MnO2 was added to the calcined powders. Samples were sintered for 2 h at 1230 and 1260 degrees C. Structural parameters, grain sizes, bulk densities and microwave dielectric parameters were determined. A monotonic decrease of the Curie temperature with the increase of strontium content was determined by low-frequency dielectric measurements. Microwave measurements around 1 GHz showed substantial decrease of the permittivity with the x increase from about 1080 to 200. Also, the variation of losses from 11 % to less than 0.2% was observed. The results indicate the BST ceramic as dielectric material, which can be utilized in paraelectric state for microwave devices. (c) 2006 Elsevier Ltd. All rights reserved.

708. Characterization of Ba0.5Sr0.5TiO3 thin films for tuneable devices

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

Published: 2007, 2006 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, +, DOI:

Barium strontium titanate (BST) bulk ceramic c 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, using 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 tit 100 kHz were performed versus temperature.

709. Memory effects in Si/SiO2/nano-crystalline PbS reterostructures

Authors: Buda, M; Stancu, V; Pentia, E; Botila, T

Published: 2007, 2006 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, +, DOI:

The mechanism of charge storage in p Si/SiO2 /nano-crystalline PbS heterostructures is investigated using capacitance - voltage (C-V) and conductance-voltage (G-V) measurements at different frequencies. The nano-crystalline thin PbS films were obtained using the Chemical Bath Deposition method with a shorter reaction time and without doping element in the reducing bath. The C-V curves show hysterezis indicating charge storage with a maximum charge density of 3x10(11) cm(-2) for the highest measurement frequency of 100 kHz. The charge storage capacity is enhanced in the rase of using a nano-crystalline PbS thin film instead of a standard macro-crystalline film.

710. Effect of temperature on the main piezoelectric parameters of a soft PZT ceramic

Authors: Miclea, C; Tanasoiu, C; Amarande, L; Miclea, CF; Plavitu, C; Cioangher, M; Trupina, L; Miclea, CT; David, C

Published: 2007, ROMANIAN JOURNAL OF INFORMATION SCIENCE AND TECHNOLOGY, 10, 250, DOI:

The temperature behavior of the main piezoelectric parameters, such as the electromechanical coupling factor k(p), the mechanical quality factor Qm, the dielectric permittivity epsilon (real and imaginary part), the loss tangent tan delta, the piezoelectric charge constants d(33) and d(31) and the voltage constants 933 and 931 of a soft type piezoelectric material was investigated. The results showed that temperatures under 150 degrees C do not influence these parameters, which indicate that every transducer made from this type of material may be successfully used up to this temperature. Between 150 degrees C and 250 degrees C, the piezoelectric properties undergo more or less important changes, mainly due to the depoling effect and above that, at temperatures over 250 degrees C, they degrade very rapidly, tending to zero.