F u n d a m entals of Piezoelectricity

Material Properties

Notes The following pages give adetailed look at piezo actuator theory and their operation. Forbasic knowledge read “QuickFacts”, p. 4-10. For definition of units, dimensions and terms,

Piezo actuators Piezo Actuators Nanopositioning & Scanning Systems Nanopositioning &Scanning Systems Active Optics / Steering Mirrors Active Optics / Steering Mirrors

see “Symbols and Units”, p. 4-7and “Glossary”, p. 4-5.

Tutorial: Piezo- electrics in Positioning
Tutorial: Piezo- electrics in Positioning Capacitive Industrial position sensors Capacitive Position Sensors

Since the piezo effect exhibited by natural materials such as quartz, tourmaline, Rochelle salt, etc. is very small, polycrys- talline ferroelectric ceramic materials such as bariumtitanate and lead (plumbum)zirconate titanate (PZT) with improved properties have been developed.PZT ceramics (piezoceramics)are available in many varia- tions and are industrial still the most widely used materials for actu- ator applications today. Before polarization, PZT crys-tallites have symmetric cubicunit cells. At temperatures below the Curie temperature, the lattice structure becomes deformed and asymmetric. The unit cells exhibit spontaneous polarization (see Fig. 5), i.e. the individual PZT crystallites are piezoelectric. Groups of unit cells with thesame orientation are calledWeiss domains. Because of the random distribution of the domain orientations in the ceramic material no macro- scopic piezoelectric behavior is observable. Due to the ferro- electric nature of the material, it is possible to force perma- nent alignment of the differentdomains using a strong electricfield. This process is called pol- ing (see Fig. 6). Some PZT ceramics must be poled at an elevated temperature. The ma- terial now has a remnant polar- ization (which can be degraded by exceeding the mechanical, thermal and electrical limits of the material). The ceramic nowexhibits piezoelectric proper- ties and will change dimen- sions when an electric potential is applied.

Piezo Drivers & Nano- positioning controllers Piezo Drivers & Nano-positioning Controllers Hexapods / Micropositioning Hexapods /Micropositioning Photonics Alignment Solutions Photonics Alignment Solutions Motion controllers Motion Controllers Ceramic Linear motors & Stages Ceramic Linear Motors & Stages Index Index
Fig. 5. PZT unit cell: 1) Perovskite-type lead zirconatetitanate (PZT) unit cell in the sym- metric cubic state above the Curietemperature.2) Tetragonally distorted unit cell belowthe Curie temperature. Fig. 6. Electric dipoles in domains; (1) unpoled ferroelectric ceramic, (2) during and (3) after poling (piezoelectric ceramic).

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