Assessing locomotion deficiency in broiler chicken

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Synthesis and sintering of PZT ceramics

Lead zirconate powder, with Zr/Ti ratio of 50/50 was prepared by polymeric precursor method and doped with 3, 5 and 7 mol% of Sr+2 Or Ba+2, as well as by 0.2 to 5 mol% of Nb+5. The powder was calcined at 750 degrees C by 4 hours and milled during 1.5 h in isopropilic alcohol. Powders were characterized by surface area measurements (BET method), by infrared spectroscopy and by X-ray diffraction to characterize the crystal structure. Isostatically pressed samples were sintered in a dilatometer furnace by using a constant heating rate of 10 degrees C/min from ambient to 1200 degrees C. Synthetic air and air with water vapor were used as atmospheres. Both Sr+2 and Ba+2 substitute Pb+2 and favor the formation of rhombohedral phase. Otherwise, Nb+5 substitute preferentially Zr+4 favoring tetragonal phase. The concentration of dopants and the atmosphere influence the densification and the microstructure of the PZT, which alters the dielectric and piezoelectric properties of the ceramics.

GCHF basis sets and their application in the electronic structure study of PrMnO3

The approach called generator coordinate Hartree-Fock (GCHF) method is used in the selection of Gaussian basis set [25s18p for O ((3)p), 31s21p14d for Mn (S-6), and 33s22p16d9f for Pr ((4)J)] for atoms. The role of the weight functions in the assessment of the numerical integration range of the GCHF equations is shown. These basis sets are contracted to (25s18p/9s5p), (31s21p14d/9s6p4d), and (33s22pl6d9f118sl2p5d3f) by segmented contraction scheme of Dunning and they are utilized in calculations of Restricted-Open-HF (ROHF) Total and Orbital energies of the (MnO+1)-Mn-3 and (PrO+1)-Pr-1 fragments, to evaluate their quality in molecular studies. The addition of one d polarization function in the contracted (9s5p) basis set for O(P-3) atom and their application with the contracted (9s6p4d), (18s21p5d3f) basis sets for Mn (S-6) and Pr-Pr ((4)j) atoms lead to the electronic structure study of PrMnO3. The dipole moment, the total energy, and total atomic charges properties were calculated and were carried out at ROHF level with the [PrMnO3](2) fragment. The calculated values show that PrMnO3 does not present piezoelectric properties. (C) 2004 Elsevier B.V. All rights reserved.

Gaussian basis sets to the theoretical study of the electronic structure of perovskite (LaMnO3)

The Generator Coordinate Hartree-Fock (GCHF) method is applied to generate extended (20s14p), (30s19p13d), and (31s23p18d) Gaussian basis sets for the 0, Mn, and La atoms, respectively. The role of the weight functions (WFs) in the assessment of the numerical integration range of the GCHF equations is shown. These basis sets are then contracted to [5s3p] and [11s6p6d] for 0 and Mn atoms, respectively, and [17s11p7d] for La atom by a standard procedure. For quality evaluation of contracted basis sets in molecular calculations, we have accomplished calculations of total and orbital energies in the Hartree-Fock-Roothaan (HFR) method for (MnO1+)-Mn-5 and (LaO1+)-La-1 fragments. The results obtained with the contracted basis sets are compared with values obtained with the extended basis sets. The addition of one d polarization function in the contracted basis set for 0 atom and its utilization with the contracted basis sets for Mn and La atoms leads to the calculations of dipole moment and total atomic charges of perovskite (LaMnO3). The calculations were performed at the HFR level with the crystal [LaMnO3](2) fragment in space group C-2v the values of dipole moment, total energy, and total atomic charges showed that it is reasonable to believe that LaMnO3 presents behaviour of piezoelectric material. (C) 2003 Elsevier B.V. All rights reserved.

Soft chemical deposition of BiFeO3 multiferroic thin films

BiFeO3 thin films free of secondary phases were obtained by the soft chemical solution on Pt(111)/Ti/SiO2/Si substrates after annealing at 500 degrees C for 2 h. The film grown in the (100) direction presented a remanent polarization P-r of 31 mu C/cm(2) at room temperature. Electrical measurements using both quasistatic hysteresis and pulsed polarization confirm the existence of ferroelectricity with a switched polarization of 60-70 mu C/cm(2), Delta P=(P-*-P). Low leakage conduction and an out-of-plane piezoelectric (d(3)) coefficient of 40 pm/V were obtained by the improvement of preparation technology.

Hyperfine interaction measurements on ceramics: PZT revisited

The solid solution of PbZr1-xTixO3, known as lead-zirconate titanate (PZT), was probably one of the most studied ferroelectric materials, especially due to its excellent dielectric, ferroelectric and piezoelectric properties. The highest piezoelectric coefficients of the PZT are found near the morphotropic phase boundary (MPB) (0.46 <= x <= 0.49), between the tetragonal and rhombohedral regions of the composition-temperature phase diagram. Recently, a new monoclinic phase near the MPB was observed, which can be considered as a bridge between PZT's tetragonal and rhombohedral phases. This work is concerned with the study of the structural properties of the ferroelectric PZT (Zr/Ti = 52/48, 53/47) by hypertine interaction (HI) measurements obtained from experiments performed by using the nuclear spectroscopy time differential perturbed angular correlation (TDPAC) in a wide temperature range. (c) 2006 Elsevier B.V. All rights reserved.

Nature of defects for bismuth layered thin films grown on Pt electrodes

The authors investigated the influence of defects on the piezoelectric and dielectric properties of Bi4Ti3O12 (BIT), SrBi4Ti4O15 (SBTi) and CaBi4Ti4O15 (CBTi144) thin films by x-ray photoemission spectroscopy measurements. In the SBTi film, Sr which is a nonpolarizable ion restricting the movement of Ti4+ ions and thus leads to a low piezoresponse. Meanwhile, the oxygen environment is quite different in the BIT and CBTi144 films exhibiting excellent piezoelectric properties. The piezoelectric coefficient and the dielectric behavior were larger for a-b axis oriented than for c axis-oriented films due to the defects created during the films crystallization. (c) 2007 American Institute of Physics.

Characterization and application of PZT/PU and graphite doped PZT/PU composite

Composites, made of lead zirconate titanate (PZT) ceramic powder and castor oil-based polyurethane (PU), were prepared in the film form. The films were obtained in the thickness range 100-300 mum using up to 50/50 vol.% of ceramic. Another composite (PZT/C/PU) was obtained by adding a small amount (1.0 vol.%) of graphite (C) to the PZT/PU composite. By increasing the conductivity of PU-containing graphite, polarization of PZT could be carried out with better efficiency. A comparison of piezo- and pyroelectric activities and spatial distribution of polarization between graphite doped and undoped composites reveal the advantages of using semiconductor filler. These composites were used as sensors to detect acoustic emission (AE). The detection was made using two simulated sources of AE, i.e., ball bearing drop and pencil lead break. PZT/C/PU composite was able to detect both flexural and extensional components of wave vibration. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Composites PVDF-TrFE/BT used as bioactive membranes for enhancing bone regeneration

In this paper a piezoelectric composite membranes were developed for charge generator to promoter bone regeneration on defects sites. Is known that the osteogenesis process is induced by interactions between biological mechanisms and electrical phenomena. The membranes were prepared by mixing Barium Titanate (BT) powders and PVDF-TrFE (PVDF:TrFE = 60:40 mol%) on dimethylformamide medium. This precursor solution was dried and crystallized at 100degreesC for 12 hours. Composites membranes were obtained by following methods: solvent casting (SC), spincoating (SP), solvent extraction by water addition (WS) and hot pressing (HP).The microstructural analysis performed by SEM showed connectivity type 3-0 and 3-1 with high homogeneity for samples of ceramic volume fraction major than 0.50. Powder agglomerates within the polymer matrix was evidenced were observed for composites with the BT volume fraction major than 40%. The composite of ceramic fraction of 0.55 presented the best values of remanent polarization (similar to33 muC/cm(2)), but the flexibility of these composites with the larger ceramic fraction was significantly affected.For in vivo evaluation PVDF-TrFE/BT 90/10 membranes with 3cm larger were longitudinally implanted under tibiae of male rabbit. After 21 days the animals were sacrificed. By histological analyses were observed neo formed bone with a high mitotic activity. In the interface bone-membrane was evidenced a pronounced callus formation. These results encourage further applications of these membranes in bone-repair process.

Investigation of piezoelectricity in perovskite (LaFeO3): A theoretical study

In a previous report we studied theoretically the piezoelectric effect in barium titanate (BaTiO3) [O. Treu Filho, J.C. Pinheiro, R.T. Kondo, J. Mol. Struct. (THEOCHEM), 671 (2004) 71]. In this article we applied the Hartree-Fock (HF) theory in the investigation of piezoelectricity in LaFeO3. Initially, the generator coordinate HF (GCHF) method was used to build 22s14p, 30s19p13d, and 32s24p17d Gaussian basis sets for O(3p), Fe(D-5), and La(D-2) atoms. Then those basis sets were contracted to [7s6p], [13s8p6d], and [18s13p7d], respectively. The quality of the contracted basis sets in polyatomic calculations was evaluated through calculations of total and orbital energies (HOMO and HOMO-1) of (FeO1+)-Fe-2 and (LaO1+)-La-1. Finally, the contracted basis sets were supplemented with polarization and diffuse functions and used to investigate the piezoelectricity in LaFeO3. The calculated properties were dipole moment, total energy, and atomic charges and the analysis of those properties showed that covalent bonds constitute the electronic structure of [LaFCO3](2) fragment. Therefore, it is reasonable to believe that LaFeO3 does not present piezoelectric properties. (C) 2006 Elsevier B.V. All rights reserved.

Electromechanical properties of calcium bismuth titanate films: A potential candidate for lead-free thin-film piezoelectrics

CaBi4Ti4O15 (CBTi144) thin films were evaluated for use as lead-free thin-film piezoelectrics in microelectromechanical systems. The films were grown by the polymeric precursor method on (100)Pt/Ti/SiO2/Si substrates. The a/b-axis orientation of the ferroelectric film is considered to be associated with the preferred orientation of the Pt bottom electrode. The P-r and E-c were 14 mu C/cm(2) and 64 kV/cm, respectively, for a maximum applied field of 400 kV/cm. The domain structure was investigated by piezoresponse force microscopy. The film has a piezoelectric coefficient, d(33), equal to 60 pm/V and a current density of 0.7 mA/cm(2).

Fabrication and testing of a poly(vinylidene fluoride) (PVDF) microvalve for gas flow control

A microactuator made from poly(vinylidene fluoride) (PVDF), a piezoelectric polymer, was fabricated to control the gas flow rate through a glass micronozzle. The actuator was formed by gluing together two PVDF sheets with opposite polarization directions. The sheets were covered with thin conducting films on one side, that were then used as electrodes to apply an electric field to move the valve. The actuator has a rectangular shape, 3 mm x 6 mm. The device was incorporated with a micronozzle fabricated by a powder blasting technique. Upon applying a DC voltage across the actuator electrodes, one sheet expands while the other contracts, generating an opening motion. A voltage of +300 V DC was used to open the device by moving the actuator 30 mu m, and a voltage of -200 V DC was used to close the device by moving the actuator 20 mu m lower than the relaxed position. Flow measurements were performed in a low-pressure vacuum system, maintaining the microvalve inlet pressure constant at 266 Pa. Tests carried out with the actuator in the open position and with a pressure ratio (inlet pressure divided by outlet pressure) of 0.5, indicated a flow rate of 0.36 sccm. In the closed position, and with a pressure ratio of 0.2, a flow rate of 0.32 sccm was measured.

Voltage responsivity of pyroelectric sensor

Composites polymer-ceramic using castor oil-based polyurethane (PU) as non-ferroelectric matrix and Lead Zirconate Titanate (PZT) as ceramic powder have been prepared at thin films form by spin coating. The samples are poled by appropriated electric field to show piezo and pyroelectric activity. The pyroelectric coefficient p(T) at 343 K is obtained to be equal 5.8 X 10(-5) C m(-2) K-1 for a composite with 32 vol.% of ceramic. The figure of merit of this composite is six times higher than of PZT ceramic. The voltage responsivity of the pyroelectric is reduced when the thickness of the sample increases. It was used modulated white light as radiation source to excite the sensor film. The electric signal of the sensor decreases with the light modulation frequency by 1/f. (C) 1999 Elsevier B.V. S.A. All rights reserved.

High Curie point CaBi2Nb2O9 thin films: A potential candidate for lead-free thin-film piezoelectrics

CaBi2Nb2O9 (CBNO) thin films deposited on platinum coated silicon substrates by the polymeric precursor method exhibited good structural, dielectric, and piezoelectric characteristics. Capacitance-voltage measurements indicated good ferroelectric polarization switching characteristics. Remanent polarization and drive voltage values were 4.2 mu C/cm(2) and 1.7 V for a maximum applied voltage of 10 V. The film has a piezoelectric coefficient d(33) equal to 60 pm/V, current density of 0.7 mu A/cm(2), and Curie temperature of 940 degrees C. The polar-axis-oriented CBNO is a promising candidate for use in lead-free high Curie point in ferroelectric and piezoelectric devices. (c) 2006 American Institute of Physics.

An approach to analyzing synthesis, structure and properties of bismuth titanate ceramics

The family of bismuth titanate, Bi(4)Ti(3)O(12) (BIT) layered-structured ferroelectrics materials is attractive from the viewpoint of such as their application as electronic materials dielectrics, piezoelectrics and pyroelectrics, because they are characterized by good stability of piezoelectric properties, a high Curie temperature and a good resistance vs temperature. Bismuth titanate (Bi(4)Ti(3)O(12)) powders can be prepared using different methods, depending if the creation will be film coating or ceramics. The structure and properties of bismuth titanate materials show a significance dependence on the applied synthesis method. In this review paper, we made an attempt to give an approach to analyszing the structure, synthesis methods and properties of bismuth titanate ferroelectrics materials.