Qualitative distinction in enhancement of the piezoelectric response in PbTiO3 in proximity of coercive fields:: 90° versus 180° switching

Piezoelectric properties of ferroelectric crystals can be greatly enhanced in the proximity of electric and mechanical coercive fields. While the thermodynamic origin of the enhancement in both cases can be traced to the flattening of a free energy profile, we show using the Landau-Ginzburg-Devonshire theory that there is a qualitative difference in how the proximity of 90 degrees and 180 degrees polarization switching affects the piezoelectric response and its anisotropy. Taking as an example PbTiO3 monodomain single crystals biased by near-coercive electric and stress fields applied along the polar axis, it is shown that the antiparallel electric field softens the material along the polar direction while the compressive stress softens the crystal along nonpolar directions. In the former cases the piezoelectric enhancement is dominated by the polarization contraction along the polar axis while in the latter case it is dominated by the polarization rotation away from the polar axis. An analogy is made between the effects of polarization switching and thermally induced phase transitions on the piezoelectric anisotropy. (c) 2007 American Institute of Physics.