Claudio Capiani

A microstructural study of porous piezoelectric ceramics obtained by different methods

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.

Pyrochlore phase and microstructure development in lead magnesium niobate materials

Abstract Microstructure characteristics of powder and sintered samples of lead magnesium niobate (PMN) have been compared and related to the presence or not of pyrochlore phase. Two kinds of samples obtained from two different batches of powders, batch A and B, containing 1 and 0 vol.% of pyrochlore phase respectively, were analysed. The two powders show the same morphology. The sintered samples, with pyrochlore content around 13 vol.% for samples from batch A and 0 vol.% for samples from batch B, exhibit totally different microstructures The grain size increases drastically from about 1 μm for samples with pyrochlore to 4–5 μm for pyrochlore free samples although starting from powders with same granulometry. The maximum dielectric constant of samples as fired, ground and annealed were measured and related to microstructures and amount of pyrochlore. On the basis of these results and data reported in literature, mostly relating dielectric properties to stoichiometry of the starting powder, it has been hypothesised that different sintering mechanisms come into play and govern the microstructure. Consequently the dielectric properties obtained were correlated to the sintering mechanism occurred rather than to the absolute value of pyrochlore phase present, as its commonly accepted.

Improvement of Piezoelectric Properties through Post Hipping

Lead-zirconate-titanate materials added with donor dopants either in the A and B site were obtained by conventional solid state reaction of the starting oxides followed by hot isostatic pressing for two hours at 950°C and 100 MPa after sintering. The post HIPping temperature was 300°C under the sintering temperature so as to sligthly influence the morphology of grains, while the residual porosity was completely removed. The elastic, dielectric, and piezoelectric characteristics of post-hipped samples were enhanced in comparison to the as sintered samples (e.g. d33 and kp increase about 5 and 8%, respectively) in agreement with the improved microstructure.