A constitutive model is developed for the non-linear switching of ferroelec
tric polycrystals under a combination of mechanical stress and electric fie
ld. It is envisaged that the polycrystal consists of a set of bonded crysta
ls and that each crystal comprises a set of distinct crystal variants. With
in each crystal the switching event, which converts one crystal variant int
o another, gives rise to a progressive change in remanent strain and polari
sation and to a change in the average linear electromechanical properties.
It is further assumed that switching is resisted by the dissipative motion
of domain walls. The constitutive model for the progressive switching of ea
ch crystal draws upon elastic-plastic crystal plasticity theory, and a pres
cription is given for the tangent moduli of the crystal, for any assumed se
t of potentially active transformation systems. A self-consistent analysis
is used to estimate the macroscopic response of tetragonal crystals (repres
entative of lead titanate) under a variety of loading paths. Also, the evol
ution of the 'switching surface' in stress-electric field space is calculat
ed. Many of the qualitative features of ferroelectric switching, such as bu
tterfly hysteresis loops, are predicted by the analysis. (C) 1999 Elsevier
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