Experimental and theoretical study of the ferroelectric and piezoelectric behavior of strontium-doped PZT

Theoretical data using ab initio perturbed ion calculation were compared with ferroelectric and piezoelectric experimental data of strontium doped PZT. Various concentrations of SrO in PZT at constant temperature and sintering time were carried out. Experimental results, such as the remanent polarization, P-R of 6.9-8.9 muC/Cm-2, the coercive field, E-C of 6.6-7.8 kVcm, and the planar coupling factor, Kp of 0.45-0.53, were compared with the energy of Zr4+ and Ti4+ ion dislocation and the lattice interaction energy which show that strontium increment in PZT alter the energies and increase the values of piezoelectric and ferroelectric variables. Calculations of lattice energy of the rhombohedral phase show that a phase non-stability is coincident with increasing experimental values of the P-R, E-C and Kp. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

Dielectric and piezoelectric properties of the mechanochemically prepared PZT ceramics

Mechanochemical synthesis was applied to obtain nanocrystalline powders of composition Pb(Zr0.52Ti0.48)O-3 (PZT). Milling was performed in a planetary ball mill using vials and balls made of zirconia or steel-in order to investigate influence of milling media on the electrical properties of resulting ceramics. PZT ceramics showed high values for dielectric constant (epsilon(r)), reaching 970 at room temperature, as well as low dielectric loss (tandelta) under the optimal processing conditions. High values of remanent polarization (P-r) indicate high internal polarizability. The best samples showed piezoelectric strain constant d(33) = 347 pC/N and planar coupling factor k(P) = 0.44. Milling in ZrO2 medium prevents powder contamination and provides reproducibility of milling process. Also, PZT obtained from the powders milled in ZrO2 exhibited lower values of dielectric loss, in comparison with the PTZ obtained from the powders milled in Fe. This suggests that contamination of the powder with Fe could result in an increase of conductivity in final product. (C) 2004 Kluwer Academic Publishers.

Piezoelectric properties of Bi4Ti3O12 thin films annealed in different atmospheres

Bismuth titanate (Bi4Ti3O12-BIT) films were evaluated for use as lead-free piezoelectric thin-films in micro-electromechanical systems. The films were grown by the polymeric precursor method on Pt/Ti/SiO2/Si (1 0 0) (Pt) bottom electrodes at 700 degrees C for 2 h in static air and oxygen atmospheres. The domain structure was investigated by piezoresponse force microscopy (PFM). Annealing in static air leads to better ferroelectric properties, higher remanent polarization, lower drive voltages and higher piezoelectric coefficient. on the other hand, oxygen atmosphere favors the imprint phenomenon and reduces the piezoelectric coefficient dramatically. Impedance data, represented by means of Nyquist diagrams, show a dramatic increase in the resistivity for the films annealed in static air atmopshere. (c) 2006 Elsevier Ltd. All rights reserved.

Collagen-hydroxyapatite films: piezoelectric properties

In this paper we report a study of the physicochemical, dielectric and piezoelectric properties of anionic collagen and collagen-hydroxyapatite (HA) composites, considering the development of new biomaterials which have potential applications in support for cellular growth and in systems for bone regeneration. The piezoelectric strain tensor element d(14), the elastic constant s(55) and the dielectric permittivity 8(11), were measured for the anionic collagen and collagen-HA films. The thermal analysis shows that the denaturation endotherm is at 59.47 degreesC for the collagen sample. The collagen-HA composite film shows two transitions, at 48.9 and 80.65 degreesC. The X-ray diffraction pattern of the collagen film shows a broad band characteristic of an amorphous material. The main peaks associated to the crystalline HA is present in the sample of collagen-HA. In the collagen-HA composite, one can also notice the presence of other peaks with low intensities which is an indication of the formation of other crystalline phases of apatite. The scanning electron photomicrograph of anionic collagen membranes shows very thin bundles of collagen. The scanning electron photomicrography of collagen-HA film also show deposits of hydroxyapatite on the collagen fibers forming larger bundles and suggesting that a collagenous structure of reconstituted collagen fibers could act as nucleators for the formation of apatite crystal similar to those of bone. The piezoelectric strain tensor element d(14) was measured for the anionic collagen, with a value of 0.062 pC N-1, which is in good agreement compared with values reported in the literature obtained with other techniques. For the collagen-HA composite membranes, a slight decrease of the value of the piezoelectricity (0.041 pC N-1) was observed. The anionic collagen membranes present the highest density, dielectric permittivity and lowest frequency constant f.L. (C) 2001 Elsevier B.V. B.V. All rights reserved.

Designing Gaussian basis sets to the theoretical study of the piezoelectric effect of perovskite (BaTiO3)

Gaussian basis sets (24s14p, 30s19p14d, and 33s21p14d for O (P-3), Ti (S-5), and Ba (S-1) atoms, respectively), are designed with the strategy of the Generator Coordinate Hartree-Fock method. The basis sets are then contracted to [6s4p], [10s5p4d], and [16s9p5d] to O, Ti, and Ba atoms, respectively, and used in calculations of total and orbital energies of (TiO+2)-Ti-1 and (BaO)-Ba-1 fragments for quality evaluation in molecular studies. For O atom, the [6s4p] basis set is enriched with d polarization function and used along with the [10s5p4d] and [16s9p5d] basis sets for the theoretical study of the piezoelectric effect of perovskite (BaTiO3). The results of this work evidence that the piezoelectric properties in BaTiO3 can be caused by electrostatic interactions. (C) 2003 Elsevier B.V. All rights reserved.

An insight into the theoretical investigation of possible piezoelectric effect in samarium titanate (SmTiO3)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

The characteristics of a nonlinear vibration neutralizer

This paper concerns an investigation into the use of cubic nonlinearity in a vibration neutralizer to improve its effectiveness. It is assumed that the frequency of the harmonic excitation is well above the resonance frequency of the machine to which the neutralizer is attached, and that the machine acts as a simple mass. It is also assumed that the response of the system is predominantly at the harmonic excitation frequency of the machine. The harmonic balance method is used to analyze the system. It is shown how the nonlinearity has the effect of shifting the resonant peak to a higher frequency away from the tuned frequency of the neutralizer so that the device is robust to mistune. In a linear neutralizer this can only be achieved by adding mass to the neutralizer, so the nonlinearity has a similar effect to that of adding mass. Some characteristic features are highlighted, and the effects of the system parameters on the performance are discussed. It is shown that, for a particular combination of the system parameters, the effect of the nonlinearity is also to increase the bandwidth of the device compared to the linear neutralizer with similar mass and damping. Some approximate expressions are derived, which facilitate insight into the parameters which influence the dynamics of the system. The results are validated by some experimental work. (c) 2012 Elsevier Ltd. All rights reserved.

Jacalin interaction with human immunoglobulin A1 and bovine immunoglobulin G1: Affinity constant determined by piezoelectric biosensoring

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The gas flow rate increase obtained by an oscillating piezoelectric actuator on a micronozzle

Micronozzles with piezoelectric actuator were fabricated and investigated. The micronozzles were fabricated in glass substrates using a powder-blasting technique, and the actuator is a bimorph structure made from a piezoelectric polymer. The actuator was located at the nozzle outlet, and was driven in an oscillating mode by applying an alternating voltage across the actuator electrodes. With a pressure difference between inlet and outlet, the gas flow rate through the device was increased. This effect was quantified, and compared to a similar micronozzle with no actuator. The increase in the flow rate was defined as the gas flow through the micronozzle with actuator oscillating minus the gas flow without actuator, was found to depend on the inlet pressure, the pressure ratio, and the nozzle throat diameter. (C) 2008 Elsevier B.V. All rights reserved.

Evaluation by Free Vibration Method of Moisture Absorption Effects in Polyamide/Carbon Fiber Laminates

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Piezoelectric behavior of SrRuO(3) buffered lanthanum modified bismuth ferrite thin films grown by chemical method

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Piezoelectric effect in composite polyurethane-ferroelectric ceramics

Flexible and free-standing films of piezoelectric composites made up of lead zirconate titanate (PZT) ceramic powder dispersed in a castor oil-based polyurethane (PU) matrix were obtained by spin coating and characterized as materials for sensor applications. The piezoelectric coefficients d 31 and d 33 were measured with the usual technique. The piezoelectric charge constant d 33 yields values up to ≤24 pC/N, even at lower PZT content (33 vol%). Some desirable properties like piezoelectricity, flexibility and good mechanical resistance show this new material to be a good alternative for use as sensors and actuators.

Joint Vibration Analysis in Patients with Articular Inflammation

The study of articular sounds using a computerized system (SonoPAK) in patients with temporomandibular disorders (TMD) of inflammatory origin revealed an increase of vibratory energy when compared to asymptomatic individuals. The following conclusions were reached: 1. The amount of vibratory energy registered in these patients ranged from 8.50 to 57.61 Hz. The major vibrations occurred in the middle of the mandibular opening cycle; 2. The mean vibratory energy measured at less than 300 Hz was between 5.70 and 48.64 Hz and at higher than 300 Hz was between 3.70 and 8.99 Hz; 3. The peak amplitude in the patients with inflammation ranged from 0.35 to 3.96 Pascal and the peak of frequency from 83.20 to 120.20 Hz.

Revisão sobre técnicas de controle em estruturas inteligentes

One of the great challenges of structural dynamics is to ally structures lighther and stronger. The great difficulty is that light systems, in general, have a low inherent damping. Besides, they contain resonance frequencies in the low frequency range. So, any external disturbance can excite the system in some resonance and the resulting effect can be drastic. The methodologies of active damping, with control algorithms and piezoelectric sensors and actuators coupled in a base structure, are attractive in current days, in order to overcome the contradictory features of these requeriments. In this sense, this article contributes with a bibliographical review of the literature on the importance of active noise and vibration control in engineering applications, models of smart structures, techniques of optimal placement of piezoelectric sensors and actuators and methodologies of structural active control. Finally, it is discussed the future perspectives in this area.