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DF: Fachverband Dielektrische Festkörper

DF 7: Advanced Dielectrics

DF 7.1: Hauptvortrag

Dienstag, 24. März 2009, 14:00–14:35, WIL A317

Origins of large piezoelectric response and lead-free alternatives to PZT — •Dragan Damjanovic — Ceramics Laboratory, Swiss Federal Institute of Technology - EPFL

One of the hottest topics in the field of piezoelectricity is replacement of ubiquitous Pb(Zr,Ti)O₃ ceramics (or PZT) with lead-free materials. The most widely adopted approach in this search for new materials is to look for systems exhibiting the same salient features as good lead-based piezoelectrics: a morphotropic phase boundary (MPB), a tendency for a large polarization rotation, and a monoclinic phase. The term *polarization rotation* has been employed only recently and has now become a synonym, together with monoclinic phases, for large piezoelectric properties. It is suggested here that *polarization rotation* is an old concept proposed over thirty years ago to explain enhanced properties of PZT in the MPB region. It is shown, using an example of lead-free material, that in addition to polarization rotation polarization extension can also lead to large electro-mechanical properties. Substantial theoretical and experimental evidence exist to show that the highest piezoelectric response does not appear in monoclinic phases but in the phase transition regions where polarization either changes direction or appears from the non-polar state. It is proposed that concept of structural instability and associated free energy instability is the most general approach that underlies theoretical results and consistently interprets experimental observations on enhancement of piezoelectric properties. Finally, perspectives of finding lead-free alternatives to PZT among presently investigated systems are discussed.