Carmen Galassi

Phase transitions and phase diagram of the ferroelectric perovskite ( Na 0.5 Bi 0.5 ) 1 − x Ba x TiO 3 by anelastic and dielectric measurements

The complex elastic compliance and dielectric susceptibility of

A microstructural study of porous piezoelectric ceramics obtained by different methods

{({\text{Na}}_{0.5}{\text{Bi}}_{0.5})}_{1\ensuremath{-}x}{\text{Ba}}_{x}{\text{TiO}}_{3}

High-field dielectric properties and Raman spectroscopic investigation of the ferroelectric-to-relaxor crossover in BaSnxTi1−xO3 ceramics

(NBT-BT) have been measured in the composition range between pure NBT and the morphotropic phase boundary included,

Preparation of concentrated aqueous alumina suspensions for tape casting

0\ensuremath{\le}x\ensuremath{\le}0.08

Ferroelectric and dielectric properties of ferrite-ferroelectric ceramic composites

. The compliance of NBT presents sharp peaks at the rhombohedral/tetragonal and tetragonal/cubic transitions, allowing the determination of the tetragonal region of the phase diagram, up to now impossible due to the strong lattice disorder and small distortions and polarizations involved. In spite of ample evidence of disorder and structural heterogeneity, the R-T transition remains sharp up to

Pyrochlore phase and microstructure development in lead magnesium niobate materials

x=0.06

Rheological characteristics of slurry controlling the microstructure and the compressive strength behavior of biomimetic hydroxyapatite

, whereas the T-C transition merges into the diffuse and relaxorlike transition associated with broad maxima of the dielectric and elastic susceptibilities. An attempt is made at relating the different features in the anelastic and dielectric curves to different modes of octahedral rotations and polar cation shifts. The possibility is also considered that the cation displacements locally have monoclinic symmetry, as for PZT near the morphotropic phase boundary.

Porous piezoelectric ceramic hydrophone

Piezoelectric porous lead zirconate titanate (PZT) ceramics prepared by different methods have been examined from a microstructural point of view. The effect of polymer volume and properties and sintering temperature on microstructure of samples and on their physical properties has been investigated. The wide range of pore volumes and pore size distributions was obtained by three different procedures: (a) reduction of the sintering temperature of the die pressed PZT samples; (b) use of a different forming technique like tape casting, starting from slurries with high volume of organic content; (c) addition of different volume concentrations of organic polymer to the PZT powder. It has been found that varying process parameters like quantity of polymer and sintering temperature changes both final porosity as well as pore size distribution, introducing dispersion in physical property values. The differences between the microstructural aspect of samples prepared by different methods and their influence on the physical properties of the samples are presented and discussed.

PZT-based suspensions for tape casting

BaSnxTi1−xO3 solid solutions with compositions in the range x = 0–0.20 were studied by combining analysis of the field-induced dielectric and ferroelectric properties with Raman spectroscopic investigations. By combining techniques, the detection of specific features related to the ferroelectric-to-relaxor crossover with increasing Sn content is possible. Detailed tunability analysis of the x = 0.05 composition indicated that multiple components contribute to the dc-field induced permittivity response; these components are active in different temperature and field ranges and could be assigned to a few polarization mechanisms. First order reversal curves (FORC) for the material clearly show a transition from ferroelectric-to-relaxor behavior with increasing x, confirming the conclusions from the Raman and dielectric studies. This was evidenced by the shift of the FORC distribution over coercivities toward zero field values. Raman measurements allow the identification of the separate phases with varying Sn ...

Tailoring non-linear dielectric properties by local field engineering in anisotropic porous ferroelectric structures

Abstract Aqueous suspensions suitable for the tape casting of alumina were produced, such that ceramic bodies with very high final sintered densities were obtained (100% of theoretical). This enables high purity, smooth, substrates to be produced without using environmentally damaging solvents. To prevent competitive adsorption of the binder with the dispersant, which leads to an increase in the viscosity and in the elastic modulus of the suspension, the binder was mixed very slowly for a short time in a ball mill. In the presence of the binder the optimum amount of dispersant was 0.3 mg m −2 (dry weight basis). These suspensions were not thixotropic. The minimum amount of binder required to produce a flexible, robust tape was established from tape casting experiments, as was the minimum amount of binder required to produce a tape that did not crack on drying. All suspensions were cast with both blades set at a gap of 0.4 mm and a Mylar tape speed of 20 cm min −1 ; the removal of air bubbles was achieved by exposing the slip to a vacuum for a few minutes. The final sintered density could be correlated directly with the volume fraction of powder (at a fixed binder content) and directly with the binder content (at fixed volume fraction). Sintering the discs revealed a greater shrinkage in the thickness direction than laterally owing to the non-spherical nature of the particles. However no correlation could be found between the thickness of the green body after casting/drying and the suspension viscosity.