National Institute Of Materials Physics - Romania

Publications

849 articles found

791. Chemically prepared nanocrystalline PbS thin films

Authors: Pentia, E; Pintilie, L; Matei, I; Botila, T; Ozbay, E

Published: JUN 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 530, DOI:

PbS nanocrystalline thin films were prepared by Chemical Bath Deposition (CBD) technique. A comparative study between "standard" and "nanocrystalline" PbS thin films was performed. We denoted "standard" the PbS film with a good photosensitivity for to use as IR detector. This film was deposited after 1 hour from chemical bath containing reducing agent and Bi ions as doping element. The "nanocrystalline" film was obtained at shorter reaction time (after 17 minutes) from reducing bath without doping element. The other parameters: concentration of the reactants, pH, temperature were kept constant for the all depositions. The morphological properties of the films were determined by SEM analysis. Also, the electrical and photoelectrical behaviors were investigated for the both types of PbS films. The "nanocrystalline" film had a very high electrical resistance (10(10)-10(11)Omega/square) compared with the "standard" film (10(5)-10(6)Omega/square). Both types of films proved to be sensitive to the surrounding atmosphere, air or vacuum. Thermally Stimulated Current (TSC) measurement had shown the presence of trap concentration in the both cases, probably due to the large amount of disordered regions.

792. Influence of Sb3+ ions on photoconductive properties of chemically deposited PbS films

Authors: Pentia, E; Pintilie, L; Tivarus, C; Pintilie, I; Botila, T

Published: MAR 22 2001, MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY, 80, 26, DOI: 10.1016/S0921-5107(00)00578-X

PbS films were obtained on glass substrates using the chemical bath deposition (CBD) method. The infrared (IR) photosensitivity increases of about 1000 times when a reducing agent (hydroxylamine hydrochloride NH2OHHCl) is added in the deposition bath. A further enhancement was tried by adding small amounts of antimony chloride (SbCl3) solution in the deposition bath. The result was just opposite. It was found that the photosensitivity decreases with increasing the Sb salt content. The changes in PbS photoconjuctive properties are correlated with the changes in film morphology due to the two compounds added in the bath - the reducing agent and the Sb salt. (C) 2001 Elsevier Science B.V. All rights reserved.

793. Ferroelectrics: new wide-gap materials for UV detection

Authors: Pintilie, L; Pintilie, I

Published: MAR 22 2001, MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY, 80, 391, DOI: 10.1016/S0921-5107(00)00605-X

Photoconductive properties of some sol-gel deposited. ferroelectrie thin films are investigated in the ultraviolet (UV) domain. The investigated materials are: Bi4Ti3O12 (BiT), SrBi2Ta2O9 (SBT) and Pb(Zr0.45Ti0.55)O-3 (PZT). It was found that all these materials exhibit pronounced photoconductivity in the 250-500 nm domain. The best current responsivity was obtained for Bi4Ti3O12 (BiT) films. (C) 2001 Elsevier Science B.V. All rights reserved.

794. Advanced technology for making PZT type ceramics by fast firing

Authors: Miclea, C; Tanasoiu, C; Miclea, CF; Amarande, L; Iorgulescu, R; Tanasoiu, V; Moscu, S

Published: MAR 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 87, DOI:

Densification and piezoelectric performances of some fast fired lead zirconate-titanate ceramics were investigated in comparison with those made by conventionally sintering technique. Micro and nano PZT powders were used as initial powders for the compacts subjected to the Cast and conventionally sinterings. Density maxims of about 98 % of the theoretical density, were obtained for nanopowder compacts fast fired at 1350 degreesC for 20 minutes. The piezoelectric properties of the fast fired and conventionally sintered compacts were determined. Significant increase for d(33) piezoelectric charge constant was observed in the case of fast fired samples compared to conventionally sintered ones. The electromechanical planar coupling factor k(p) was also increased From 0.62 to 0.65 for fast fired samples. The densification mechanism was discussed in terms of a predominantly transient stresses induced during the initial stage of densification by the rather high temperature gradient of the fast fired samples.

795. Investigations of pyroelectric properties of pure and alanine doped TGS crystals

Authors: Costache, M; Matei, I; Pintilie, L; Alexandru, HV; Berbecaru, C

Published: MAR 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 81, DOI:

Pyroelectric measurements were performed on pure and on L or D alanine doped TCS. Crystals were grown in paraelectric phase (similar to 52 degreesC) from solutions by slow evaporation of the solvent. Pyroelectric current was measured by, crossing the Curie point, both on heating and cooling. Spontaneous polarization P-S(T) was also recorded using the charge integration method. The pyroelectric current of pure TGS samples along with the spontaneous polarization were detected only on heating, using a poling procedure similar to those applied to ceramic ferroelectrics. The remarkable asymmetry of measured pyroelectric coefficient of D and I. alanine doped samples suggests a non-equivalent substitution of glycine in the host lattice.

796. Thermally stimulated current method applied on diodes with high concentration of deep trapping levels

Authors: Pintilie, I; Pintilie, L; Moll, M; Fretwurst, E; Lindstroem, G

Published: JAN 22 2001, APPLIED PHYSICS LETTERS, 78, 552, DOI: 10.1063/1.1335852

We propose an improved method of thermally stimulated currents (TSC) spectra analysis in the case of diodes having a concentration of traps higher than that of doping impurities. Beside the calculation of trap concentrations from TSC peaks analysis, the method allows us to evaluate the density and the type of the very deep trapping level which, due to the contribution of leakage current, can not be detected in a real TSC experiment. The proposed method is applied to a p(+)-n Silicon diode irradiated with 1.82x10(13)neutrons/cm(2). (C) 2001 American Institute of Physics.

797. Mechanical and electromechanical nonlinearities of a piezoelectric trimorph type actuator

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

Published: 2001, CAS: 2002 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, PROCEEDINGS, 74, DOI:

An experimental study was made of the mechanical and electromechanical nonlinearities of a PZT trimorph type actuator. The actuator consisted of two piezoceramic poled plates, sandwiched on a thin metallic sheet, forming the usual trimorph structure, with one end fixed and the other one free. The experiments were conducted in two steps. In the first step a force was applied to the free end of the trimorph and its displacement was measured as a function of the applied force either for increasing and decreasing force. The nonlinearities in this case must be pure mechanical and they give information about the structural arrangement of the piezoceramic elements, glue and metallic sheet. For the second step the actuator was electrically activated with increasing and decreasing DC voltages and the displacement of the free end was determined as a function of applied DC voltage. The nonlinearities in this case are of electromechanical nature and they were the result of the combined effect of intrinsic material nonlinearities and structural arrangement. The C, experimental results showed that pure mechanical nonlinearities are practically inexistent even for forces up to 0.7 N. The displacement of the free end follows the theoretical predictions. When the actuator was electrically activated the displacement of the free end was entirely hysteretic and the electromechanical nonlinearities were different from the theoretical predictions. The results were discussed in terms of the displacement of ferroelastic-ferroelectric domain walls.

798. Sintering behaviour of piezoceramic powders prepared by conventional ceramic and mechanical activation process

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

Published: 2001, 2001 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOL 1 & 2, PROCEEDINGS, 300, DOI: 10.1109/SMICND.2001.967469

Conventional and mechanical activation techniques were used to prepare a soft PZT type piezoceramic material. The resulting powders exhibit micro and nanostructures, respectively as indicated by X-ray and electron microscopy. Average crystallite sizes of 1 mu and 50 nm respectively were estimated for the powders. The sintered behavior of pressed samples from the two types of powders was investigated within the 8001300 degreesC temperature range and the densities, structural morphology and dielectric and piezoelectric properties were investigated. Optimum sintering temperature were about 100 degreesC lower for samples made from mechanical activated powder compared to the conventionally ones. Sintered samples from this powder exhibited also enhanced properties compared to those made from the conventionaly prepared powder. It is concluded that the mechanical activation technique is a reliable and simple method to prepare high quality PZT type materials.

799. Equivalent pyroelectric coefficient of a pyroelectric bimorph structure

Authors: Pintilie, L; Pintilie, I; Matei, I

Published: DEC 15 2000, JOURNAL OF APPLIED PHYSICS, 88, 7271, DOI: 10.1063/1.1327284

A detailed formula for the equivalent pyroelectric coefficient of a bimorph structure acting as a pyroelectric detector was deduced. It is shown that electric fields occur in the structure when it is subjected to a temperature variation, due to the unequal charges generated by the two components. The field dependence of the ferroelectric polarization has to be considered in this case and the (partial derivativeP/partial derivativeE) derivative appears explicitly in the deduced formula. The effect is that the equivalent pyroelectric coefficient has different values for heating and cooling. This could lead to a redressing effect on the pyroelectric signal if the temperature difference varies periodically. The equivalent pyroelectric coefficient is, also, thickness dependent. This fact offers the possibility of designing structures with high values of pyroelectric coefficient compared with the values of the component phases. (C) 2000 American Institute of Physics. [S0021- 8979(00)04701-6].

800. Ferroelectric properties of Pb1-3y/2Lay(Zr0.4Ti0.6)O-3 structures with La concentration gradients

Authors: Boerasu, I; Pintilie, L; Kosec, M

Published: OCT 2 2000, APPLIED PHYSICS LETTERS, 77, 2233, DOI: 10.1063/1.1313814

Graded ferroelectric (GF) structures were obtained by successive deposition of Pb1-3y/2Lay(Zr0.4Ti0.6)O-3 films with different La contents on Pt/TiO2Si substrates. The method used for deposition was sol gel. The final structure consists of four layers, starting from the Pt electrode to the top gold electrode: (1) no La; (2) 4% La; (3) 8% La; and (4) 12% La. Ferroelectric properties of the GF structure were investigated, and an anomalous shift of the hysteresis loop along the polarization axis was found. The sense of this shift depends on the initial direction of the ferroelectric polarization. The presence of hysteresis displacement "up" or "down" can be explained if the presence of a built-in charge in the GF structure is admitted. The built-in potential produced by this charge is computed using a simple theoretical model. (C) 2000 American Institute of Physics. [S0003-6951(00)01040-8].