Advanced Materials Forum III

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Authors: Lucjan Kozielski, Agata Lisińska-Czekaj, Dionizy Czekaj
Abstract: Piezoelectric transformer (PT) is a combination of piezoelectric actuator and transducer, which serve as the primary side and the secondary side respectively. In the present study the disk – shaped (of 20 mm in diameter and 0.6 mm in thickness), unipoled radial mode piezoelectric transformer based on modified PZT-type solid solution was custom designed and fabricated. Different input and output area ratios of the PT were studied, namely: 21, 4, 1. The electrical properties like voltage step-up ratio, output power and temperature rise were measured for PT operating at the first resonance frequency. With the driving voltage of 20 VRMS, the 3 W output power, 165 VRMS output voltage an temperature rise of 20 0C was obtained for PT with the input/output area ratio of 1. The voltage step-up ratio of 12.5 was obtained for PT with input/output area ratio of 21.
Authors: Hélder F. Castro, Senentxu Lanceros-Méndez, José Gerardo Rocha
Abstract: One of the main problems for the use of ferroelectric materials for sensor applications, especially for tactile sensors, is the separation of the pyro- and piezoelectric responseproduced by temperature and pressure changes, respectively. We present two different approaches to achieve this goal. The first approach is based on the study of the signal in the frequency domain and uses a signal processing to separate the approach is based on a double layer configuration of electroactive polymers. In this case, the piezoelectric response is equal in each layer, whereas, the pyroelectric response dominates in the layer exposed to the temperature variations. The pyro- and piezoelectric responses are separated by estimating the diference between the signals of two layers and the signal from one of the layers, correspondingly.
Authors: Fátima Cardoso, Bernardo G. Almeida, Pedro Caldelas, Jorge A. Mendes
Abstract: The ferroelectric polymorph of lead metaniobate (PbNb2O6) presents an orthorhombic structure that is metastable at room temperature. This phase is obtained by quenching from high temperature. The fabrication of lead niobate thin films with this orthorhombic form has been reported to be difficult due to the presence of phases with the rhombohedric form or other nonstoichiometric phases. In this work, lead niobate thin films have been prepared by laser ablation, at different oxygen pressures and with different substrate temperatures. Their structure was studied by X-ray diffraction and their surface was examined by scanning electron microscopy (SEM). The results show that for low deposition temperatures the films presented a rhombohedric-PbNb2O6 structural phase. As Tdep increases the films started to develop an orthorhombic- PbNb2O6 structure that appeared at 400°C and remains up to 600°C. For lower oxygen pressure during deposition, a mixture of this phase and other orthorhombic lead deficient phases are present in the films. On the other hand, by increasing the oxygen pressure the lead deficient phases are strongly reduced and the films present only the orthorhombic- PbNb2O6 structure.
Authors: A.Z. Simões, M.A. Ramírez, B.D. Stojanović, Z. Marinković, Elson Longo, José Arana Varela
Abstract: The ferroelectric properties and leakage current mechanisms of preferred oriented Bi3.25La0.75Ti3O12 (BLT) thin films deposited on La0.5Sr0.5CoO3 (LSCO) by the polymeric precursor method were investigated. Atomic force microscopy indicates that the deposited films exhibit a dense microstructure with a rather smooth surface morphology. The improved ferroelectric and leakage current characteristics can be ascribed to the plate-like grains of the BLT films.
Authors: Juras Banys, Jan Macutkevic, Algirdas Brilingas, Vytautas Samulionis, K. Bormanis, Andris Sternberg, Vismantas Zauls
Abstract: Dielectric properties of 0.4PbZn1/3Nb2/3O3-0.3PbSc1/2Nb1/2O3-0.3PbMg1/3Nb2/3O3- (0.4PZN- 0.3PSN-0.3PMN) ceramics are presented for 200 < T < 500 K and 20 Hz < ν < 1 MHz. Dielectric constant is very high (more 14000) in the vicinity of the peak. Anomalous broad dielectric relaxation have been observed near the temperature of the maximum permittivity, Tm (at 1 kHz). External bias field considerably lowers the value of dielectric losses at low frequencies due to decrease of polar nano regions contribution to the dielectric permittivity.
Authors: A. Basílio, Rui Igreja, Paulo Inácio, C.J. Dias, José N. Marat-Mendes
Abstract: Ultrasonic motors are of great interest since their operation is not affected by a magnetic field. On this work the development of a prototype of a smart ultrasonic motor and its characteristics will be presented. The stator of the motor is formed by a cantilever made of PZT ceramic plate sandwiched between two unidirectional CFRP composite sheets. The composite sheets are oriented to 45º and -45º in the longitudinal direction. By application of a sinusoidal electric field to the piezoelectric ceramic plate, it vibrates. The anisotropy of the CFRP composite sheets induces an expansion/torsion movement. This effect is transformed into rotation by friction. The study of adequate voltages and frequencies of the applied electric field allows the optimization of the rotating motor performance.
Authors: Elena Dimitriu, Alin Iuga
Abstract: A PZT-type material, doped with niobium and lithium was prepared by the ceramic technique. The microstructure of the sintered material at 1280oC was performed by scanning electron microscopy (SEM), transmission electron microscopy and by X-ray diffraction. Dielectric and piezoelectric properties were measured. The good planar properties of the material made it possible to obtain ceramic disks with a strong radial mode. Two such disks, glued together, with opposed polarisation constitute a bimorf element, which successfully converts the radial mode into a flexural one. At the center of the bimorf a conical acoustical impedance adapter is fixed in order to increase the frontal acoustical emission of the device. This ultrasonic device provides a broad – band, high acoustical emission, and is suitable to work as a high efficiency ultrasonic siren. It can be used in intruder alarm devices, ultrasonic telemeters.
Authors: Vytautas Samulionis, Juras Banys, Yulian Vysochanskii
Abstract: The electromechanical properties of layered, two-dimensional materials of CuInP2S6 family have been investigated. It was shown that, at room temperature, which is above phase transition and under DC bias electric field, these materials behave as a piezoelectric because of electrostriction. In this case, the piezoelectric and electromechanical coupling coefficients are odd functions of the bias field and have a linear dependence on the bias field. The relative changes of ultrasonic velocity are found to have a quadratic dependence on the bias DC field. In bias fields of about 20 kV/m, the values of square of electromechanical coupling coefficient could be high enough (>20%) for longitudinal vibrations in thin plates of investigated CuInP2(S,Se)6 materials in the paraelectric phase. In the ferroelectric phase, the external DC electric field acts as polarizing field and electromechanical coupling coefficients sufficiently increase. At the transitions, the piezoelectric anomalies have been observed.
Authors: Robertas Grigalaitis, Juras Banys, Saulius Lapinskas, Emre Erdem, Rolf Boettcher, H. Juergen Glaesel, Eberhard Hartmann
Abstract: In this paper the dielectric properties of nanosize ferroelectric lead titanate crystals are presented. The PbTiO3 samples were prepared by pressing nanopowder into the plates and have been studied experimentally by dielectric permittivity measurements in a wide frequency and temperature range. The obtained TC dependence shows a critical change of behavior with increasing of mean nanoparticle size in a 9 nm region. The theoretical calculations based on Monte Carlo simulation were performed to describe such behavior of this material. It was shown that taking into account distribution of nanoparticle sizes in sample is possible to describe dielectric properties of PbTiO3 nanocrystals rather well.
Authors: Alexander Tkach, Branca Araújo, Paula M. Vilarinho
Abstract: The effect of the electric field on the dielectric response of the Sr1-xCaxTiO3 ceramic system was analysed and complemented by structural and microstructural studies. A monotonic decrease of the lattice parameter and an increase of the average grain size from 11 to 23 μm with increasing x were observed by X-ray diffraction and scanning electron microscopy analysis respectively. Samples with x = 0.003 and 0.01 reveal a monotonous increase of low-temperature dielectric constant, corresponding to an enhancement of the tunability and a reduction of the driving electric field at 10-30 K for x = 0.01. For Sr1-xCaxTiO3 ceramic samples with x = 0.04 and 0.10 the ferroelectric phase transition of around 20 K was observed together with the enhanced tunability of the dielectric constant at 30-85 K for x = 0.10.

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