National Institute Of Materials Physics - Romania

Publications

838 articles found

671. 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.

672. 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.

673. 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.

674. 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.

675. 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.

676. Accelerate ageing of PZT-type ceramics

Authors: Toacsan, MI; Ioachim, A; Nedelcu, L; Alexandru, HV

Published: 2007, PROGRESS IN SOLID STATE CHEMISTRY, 35, 537, DOI: 10.1016/j.progsolidstchem.2007.01.018

Accelerate ageing of lead zirconate-titanate ferroceramics (PZT) by fast neutron irradiation is investigated. The ferroelectric behavior of Pb1-wMw(Zr,Ti)O-3, where w < 0.5 wt%, M = Li, Nb, Cr, Bi, Mn, Sb, La for Zr/Ti ratio = 51.5/48.5, prepared by solid state reaction, is strongly affected by fast neutron irradiation at Phi(i) = (10(13) divided by 10(18)) n/cm(2) integrated fluxes. Structural investigations (XRD and SEM) reveal modifications of the microstructure, porosity and elementary cell parameters. High irradiation levels induce tetragonal-cubic at the same time with a ferro-paraelectric transition. The micrographs show the evolution of 90 degrees and 180 degrees walls as well as herringbone structure typical for tetragonal distortions with irradiation level. A relation between macroscopic characteristics (piezoelectric and dielectric) and microscopic properties (crystallographic parameters, porous structure and grain morphology) as function of irradiation doses can be established using a model based on microstructural parameters. These results offer opportunities to understand the fundamentals of radiation effects upon piezoelectric ceramics. (c) 2007 Elsevier Ltd. All rights reserved.

677. 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.

678. 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.

679. 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%).

680. 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.