The Role of Ferroelectricity for Piezoelectric Materials

Most of the technological applications of piezoelectricity used nowadays are based on ferroelectric materials. This is due to the following reasons:

• 1. Because of the high piezoelectric effect that can be found in these materials, a high and efficient electromechanical transformation of energy and signals can be achieved.

• 2. In general, the remnant electrical polarization that occurs in these materials can be oriented into a desired direction by applying an external electrical field: this means by poling, if needed, at elevated temperature. Therefore it becomes possible to imprint a unipolar direction of macroscopic preference or anisotropy to a device even after processing it. Obviously, this unipolarity is mandatory for every piezoelectric action.

• 3. Therefore, materials that are macroscopically isotropic by nature after the production process can be also used. This concerns, e.g., ceramics, plastics, or composites, which can be processed using well-known methods to adapt and shape the material according to the requirements of the final use.

• 4. For piezoelectric applications, the group of ceramics based on the so-called perovskite structure is especially important. These materials are already being used over a broad field of technological applications such as in capacitors and PTC resistors¹. Therefore, experience in the mass production, reliability, etc. of these materials is already available.

• 5. Therefore, also from the point of view of production cost, ferroelectric materials offer good advantages.

Consequently, it makes sense to offer here a short introduction into this class of materials.