Abstract
According to the EU-Directives 2002/95/EC, 2002/96/EC, lead-based piezoceramics must be substituted in the future with more environmentally friendly alternatives, only when a reliable alternative is found. This is why an increasing interest has grown in the research community to find lead free piezoelectric materials that fulfil the requirements for this substitution. Different families of compounds have been shown to be possible candidates for this use, such as bismuth and niobates based perovskites, pyrochlores, etc. However, a material with piezoelectric coefficients similar to those of PZT (lead zirconate titanate, Pb[ZrxTi1-x]O3) has not been yet found. Besides, each of these families has its specific characteristics in terms of remnant polarization, coercive field or application temperature. Thus, the choice of each material should be made according to the specific needs of the application. In this sense, Aurivillius-type structure materials (also known as Bismuth Layered Structure Ferroelectrics, BLSF) can take advantage of their specific properties for uses as Lead Free Piezoelectric systems. Some of them have a high Curie temperature, which make them good candidates to be used as high temperature piezoelectrics; high coercive fields, which facilitates their use as actuators; or a high switching fatigue resistance, which can be useful for future applications as Ferroelectric Random Access Memories (FERAM).
Highlights
According to the EU-Directives 2002/95/EC, 2002/96/EC, lead-based piezoceramics must be substituted in the future with more environmentally friendly alternatives, only when a reliable alternative is found
Some of them have a high Curie temperature, which make them good candidates to be used as high temperature piezoelectrics; high coercive fields, which facilitates their use as actuators; or a high switching fatigue resistance, which can be useful for future applications as Ferroelectric Random Access Memories (FERAM)
Another alternative to have dense ceramics with Aurivillius structure is to synthesize the precursors by the classical ceramic or an alternative method and prepare the ceramics by pressure-assisted sintering
Summary
Many of the peculiar characteristic properties of Aurivillius materials are determined by their crystalline structure These compounds have the general formula [Bi2 O2 ]2+ [An −1 Bn O3n+1 ]2− and are built from n pseudoperovskite layers alternating with [Bi2 O2 ]2+ layers [1]. At difference of the ferroelectrics with perovskite structure, the polarization is not produced by the displacement of the B cation within the oxygen octahedral but by relative shifts of the oxygen octahedral through the a-axis with respect to the [001] bismuth chain. They can be divided in 3 main movements, as illustrated in references [3,4,5]:.
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