Importance of a High Shear Coefficient to the Piezoelectric Properties of Domain-Engineered Crystals and Ceramics

The importance of a high shear coefficient d
₁₅
to the piezoelectric properties of domain-engineered perovskite crystals is discussed. The terms "rotator" and "extender" are introduced to differentiate the contrasting behaviors of 4mm BaTiO
₃
and PbTiO
₃
. In "rotator" ferroelectrics, where d
₁₅
is high, polarization rotation is the dominant mechanism of piezoelectric response; in "extender" ferroelectrics d
₁₅
is low and the collinear effect dominates. Large shear coefficients can be expected close to ferroelectric-ferroelectric phase transitions; this includes morphotropic phase boundaries. The differing piezoelectric properties of rotator and extender domain-engineered single crystals are discussed.