Thickness dependence of dielectric and piezoelectric properties for alternating current electric-field-poled relaxor-PbTiO ₃ crystals

Relaxor-PbTiO ₃ crystals possess ultrahigh piezoelectricity when compared with state-of-the-art Pb(Zr,Ti)O ₃ ceramics. Recently, even higher piezoelectricity is observed in alternating current electric-field-poled (AC-poled) crystals. This poling technique may benefit many piezoelectric materials and corresponding applications. The scaling effect is quite important for piezoelectric applications, since the operational frequency of devices is associated with the dimension of piezoelectric elements. Here, we investigated the thickness dependence of dielectric and piezoelectric properties for AC-poled relaxor-PbTiO ₃ crystals. Compared with the traditional poling method, the piezoelectric coefficient (d ₃₃ ) and dielectric permittivity (ϵ ^T ₃₃ /ϵ ₀ ) were found to be increased by 20%-30% via alternating current electric field poling (AC-poling). A weak scaling effect was observed for the samples with thickness above 200 μm. While, for 100-μm samples, the dielectric permittivity was only enhanced by 6%, and a clear degradation of properties was observed when the cycle of alternating current electric field is beyond three. These features are thought to be associated with the impacts of surface damages for thin samples. Of particular interest is that the coercive field was found to decrease during AC-poling, which should be considered for the design of piezoelectric devices. This work provides important information for AC-poled relaxor-PbTiO ₃ crystals and will benefit the piezoelectric applications using these crystals.