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DF: Dielektrische Festkörper

DF 4: Internal Symposium “Ferroelectric Materials for Smart Structures”

DF 4.7: Vortrag

Dienstag, 28. März 2006, 11:50–12:10, K{\"O}N Farb

Micro-mechanics of multi-variant and multi-phase ferroelectric domain structures — •Johannes Rödel — TU Dresden, Institut für Werkstoffwissenschaft

High-strain piezoelectric materials are often ceramics with a complicated constitution. In particular, PZT, but also PMN-PT and PZN-PT, are used with compositions near to a so-called morphotropic phase boundary, where not only different variants of the same phase (domains), but different phases may coexist. Micro-mechanical models for ferroelectric ceramics would be much more realistic, if these effects could be incorporated.

We consider the conditions of mechanical and electrical compatibility of ferroelectric domain structures. One result are the well known crystallographic relationships between domains of the same phase for various phases. Furthermore we are able to address the question of coexistence of different crystallographic phases within the very same crystallite. In general, the spontaneous strain and spontaneous polarization of a tetragonal and a rhombohedral ferroelecctric domain are not compatible. The internal fields which are caused by this incompatibility, and the associated energy contributions, can be calculated using distributed crystal defects and charge models. We can also show that this internal fields and energies can be decreased by an intermediate, e.g. monoclinic, phase.

The outlined approach can be used to model the overall behavior of multi-variant and multi-phase crystallites with certain, simplified geometrical arrangements of the constituents.