Monocristales de ((1 - x)Pb(Zn1/3Nb2/3)O3-xPbTiO3-(1 - x)PZN-xPT) con estructura perovskita, muestran excelentes propiedades dieléctricas, ópticas y electrostrictivas en composiciones cerca a la frontera de fase morfotrópica (FFM), x <img src="/img/revistas/ince/v10n20/v10n20a02f6.jpg"> 0;09. La preparación de cerámicas con composiciones cercanas a la FFM por métodos convencionales, conduce a cerámicas con estructura pirocloro. En este trabajo, polvos de ((1-x)Pb(Zn1/3Nb2/3)O3- xPbTiO3-PZN-xPT) con x = 0;10 fueron sintetizados por el método de reacción por combustión. Como combustibles fueron usados: CO(NH2)2, C2H5NO2, CO(NH2)2/C2H5NO2 y C4H16N6O2. El resultado indica que el mayor porcentaje de fase perovskita (<img src="/img/revistas/ince/v10n20/v10n20a02f6.jpg"> 70 %) fue obtenido usando CO(NH2)2= C2H5NO2 (razón 50/50). Esta fase es mantenida al sinterizar la muestra a 1000 ° C en atmósfera de nitrógeno.

((1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3-(1-x)PZN-xPT) single crystals with perovskite structure near to the morphotropic phase boundary (MPB), x<img src="/img/revistas/ince/v10n20/v10n20a02f6.jpg">0; 09, exhibit unusual large dielectric and piezoelectric constants. Preparation of PZN-PT ceramics with composition near to the MPB using conventional methods leads to ceramics with pyrochlore structure. In this paper, ((1 - x)Pb(Zn1/3Nb2/3)O3-xPbTiO3-PZN-xPT) powders with x = 0; 10 were synthetized by the combustion reaction method. CO(NH2)2, C2H5NO2, CO(NH2)2/C2H5NO2 y C4H16N6O2 were used as fuels. Results show that a maximum of 70% of perovskite phase was obtained using CO(NH2)2= C2H5NO2 (in relation 50/50). The afore mentioned phase is preserved when sintering the sample at 1000 ° C, during 4h on nitrogen atmosphere.

In this paper, a new method for designing a Bessel transducer is described. The method relies on the comparison between the transducer surface excitation and the theoretical Bessel function. This make it posible to select the right kerf between successive rings and obtaining the best characteristics in the radiation pattern. The field simulation is accomplished by means of the impulse response technique. The proposed method is applied to a three-ring transducer and compared with experimental results.

En el presente trabajo se presenta un nuevo método para diseñar un transductor de Bessel. El método consiste en la comparación entre la excitación sobre la cara del transductor y la función de Bessel. Esto permite seleccionar el espacio entre anillos optimo para así obtener las mejores características del campo de radiación. La simulación del campo fue llevada a cabo por medio del uso de la respuesta al impulso. El método propuesto es aplicado a un transductor de tres anillos y los resultados de la simulación son comparados con resultados experimentales.

In this study a coaxial line was used to connect a microwave-frequency Network Analyzer and a base moving sample holder for dielectric characterization of ferroelectric materials in the microwave range. The main innovation of the technique is the introduction of a special sample holder that eliminates the air gap effect by pressing sample using a fine pressure system control. The device was preliminary tested with alumina (Al2O3) ceramics and validated up to 2 GHz. Dielectric measurements of lanthanum and manganese modified lead titanate (PLTM) ceramics were carried out in order to evaluate the technique for a high permittivity material in the microwave range. Results showed that such method is very useful for materials with high dielectric permittivities, which is generally a limiting factor of other techniques in the frequency range from 50 MHz to 2 GHz.

Tungsten bonze structured lead barium niobate (Pb1-xBa xNb2O6) ferroelectric ceramics were prepared by the conventional mixed oxide method and their dielectric properties were carefully investigated. All studied samples presented elevated values of maximum dielectric constant (epsilon'm) and its corresponding temperature of maximum (Tm) in comparison with perovskite structured ones. The phase transition features indicate that the PBN samples do not present a complete diffuse phase transition. Indeed, the diffuseness degree of the ferroelectric phase transition is highly dependent of the ions Pb2+ content in the sample compositions. The diffuseness of the ferroelectric phase transition is enhanced while the temperature of maximum dielectric constant is decreased with the Pb2+ content decreasing. In addition, the maximum dielectric constant shows an opposite behavior.

The structure of polycrystalline strontium barium niobate at room temperature was refined by the Rietveld method. Sintered ceramic samples were used to collect powder neutron and X-ray diffraction data. The ratio Sr/Ba ~ 64/36 was found from the initial batch composition Sr0.61Ba0.39Nb2O6, corroborating with the quantitative X-ray dispersive spectroscopy (EDS) measurements. The structure is tetragonal with cell parameters a, b = 12.4504(3) Å and c = 3.9325(1) Å and space group P4bm. It was not necessary to introduce any positional disorder for the oxygen atoms. Cation Nb+5 displacements not parallel to the c direction are presented, which can influence the behavior of the ferroelectric properties.

Lanthanum-modified lead zirconate titanate (PLZT) ceramics were obtained with high transmittance in the visible range by a combination of an inexpensive chemical processing and hot pressing. Optical, microstructural, pyroelectric, ferroelectric and dielectric properties characterized in this study attested the applicability of the employed method in the production of PLZT transparent ferroelectric ceramics. In fact, the corresponding analyzed physical parameters are in very good agreement with those obtained in samples traditionally prepared by other methods. Furthermore, due to high sample quality, a phenomenological analysis of the PLZT 10/65/35 relaxor features was performed in these ceramics.

Strontium barium niobate (SBN) thin films of good quality were deposited on Pt/Ti/SiO2/Si substrate using a polymeric resin containing metallic ions. Films were crystallized at different temperatures and for different duration of time. The structure of these films was studied using X-ray diffraction. The coexistence of SrNb2O6 (SN) and SBN was observed in films crystallized at 700 °C. The amount of SN decreases when the crystallization time increases. Ferroelectric properties were determined for films crystallized at 700 °C for 1 and 5 h. For SBN film crystallized at 700 °C for 1 h, the remanent polarization (Pr) and the coercive field (Ec) were 2.6 muC/cm² and 71.9 kV/cm, respectively. For the film crystallized at 700 °C for 5 h these parameters were Pr = 1.1 muC/cm² and Ec = 50.5 kV/cm.

Neste trabalho, filmes finos ferroelétricos de PZT preparados pelo método dos precursores óxidos, foram depositados sobre substratos de Pt/Si. Os filmes obtidos apresentaram uma espessura média de 0,5 mm. Caracterizações dielétricas e ferroelétricas foram realizadas nesses filmes. O valor medido da constante dielétrica dos filmes foi de 455. A ferroeletricidade foi confirmada por características de Capacitância-Voltagem (C-V) e ciclos de histerese P-E. A polarização remanescente para os filmes apresentou um valor em torno de 5,0 µC/cm2 e um campo coercitivo de 88,8 kV/cm.

In this work ferroelectric thin films of PZT were prepared by the oxide precursor method, deposited on Pt/Si substrate. Films of 0.5 mm average thickness were obtained. Electrical and ferroelectric characterization were carried out in these films. The measured value of the dielectric constant for films was 455. Ferroelectricity was confirmed by Capacitance-Voltage (C-V) characteristics and P-E hysteresis loops. Remanent polarization for films presented value around 5.0 µC/cm2 and a coercive field of 88.8 kV/cm.

This work describes an alternative method for the preparation of ferroelectric thin films based on pre-calcination of oxides, to be used as precursor material for a solution preparation. In order to show the viability of the proposed method, PbZr0.53Ti0.47O3 and Bi4Ti3O12 thin films were prepared on fused quartz and Si substrates. The results were analyzed by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Infrared Spectroscopy (IR) and Rutherford Backscattering Spectroscopy (RBS). The films obtained show good quality, homogeneity and the desired stoichiometry. The estimated thickness for one layer deposition was approximately 1000 Å and 1500 Å for Bi4Ti3O12 and PbZr0.53Ti0.47O3 films, respectively.