Correlation between dielectric anisotropy and positive or zero transverse piezoelectric coefficients in perovskite ferroelectric single crystals

The transverse piezoelectric coefficient (d31⋆) has been calculated for tetragonal barium titanate (BT) and lead titanate (PT) cut along nonpolar axes, over a range of temperatures, using the phenomenological Landau-Ginzburg-Devonshire theory. It is shown that negative values of d31⋆ are favored when the transverse dielectric susceptibility η11 and shear coefficient d15 are large, such that polarization rotation is more significant than the collinear piezoelectric effect. This occurs in tetragonal BT close to its ferroelectric-ferroelectric phase transition to an orthorhombic phase. In PT, however, where no phase transition occurs, d15 is small and polarization “extension” due to d33 dominates: small or positive values of d31⋆ become prominent. This extends a previous result found for polycrystalline modified PT ceramics.