Comparative face-shear piezoelectric properties of soft and hard PZT ceramics

The face-shear (d36) mode may be the most practical shear mode in piezoelectrics, while theoretically this mode cannot appear in piezoelectric ceramics because of its transversally isotropic symmetry. Recently, we realized piezoelectric coefficient d36 up to 206pC/N in soft PbZr1-xTixO3 (PZT) ceramics via ferroelastic domain engineering [H. C. Miao and F. X. Li, Appl. Phys. Lett. 107, 122902 (2015)]. In this work, we further realized the face-shear mode in both hard and soft PZT ceramics including PZT-4 (hard), PZT-51(soft), and PZT-5H (soft) and investigated the electric properties systematically. The resonance methods are derived to measure the d36 coefficients using both square patches and narrow bar samples, and the obtained values are consistent with that measured by a modified d33 meter previously. For all samples, the pure d36 mode can only appear near the resonance frequency, and the coupled d36-d31 mode dominates off resonance. It is found that both the piezoelectric coefficient d36 and the electromechanical coupling factor k36 of soft PZT ceramics (PZT-5H and PZT-51) are considerably larger than those of the hard PZT ceramics (PZT-4). The obtained d36 of 160–275pC/N, k36 ∼ 0.24, and the mechanical quality factor Q36 of 60–90 in soft PZT ceramics are comparable with the corresponding properties of the d31 mode sample. Therefore, the d36 mode in modified soft PZT ceramics is more promising for industrial applications such as face-shear resonators and shear horizontal wave generators.