Heterogeneous domain structure induced by alternating current poling in Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystal

The thickness of the piezoelectric single crystals is known to have a significant impact on their piezoelectric properties. For high-performance transducers used in high-frequency medical diagnostic applications, the thickness of the piezoelectric single crystals must be reduced. However, the scaling effect, where the piezoelectric and dielectric properties deteriorate as the thickness decreases, remains insufficiently understood, and the mechanisms underlying this phenomenon are unclear. To address this issue, we investigated the changes in polarization and dielectric properties and the underlying mechanism of the scaling effect in alternating current (AC)-poled rhombohedral [001]-oriented 0.72Pb(Mg1/3Nb2/3)O3–0.28PbTiO3 (PMN–28PT) single crystals with respect to the sample thickness. The typical scaling effects, commonly observed with decreasing sample thickness, were confirmed through the degradations in polarization and dielectric properties of AC-poled crystals. The AC-poled crystals exhibited 109.5° domain walls parallel to the (001) plane, and the domain sizes in the surface layer were more than double those in the inner region regardless of thickness. The larger domain size in the surface layer reduces the density of the relatively soft 109.5° domain boundaries, thereby it causes an increase in the coercive field and degradation of the dielectric properties as the thickness decreases. The accumulated space charge on the surface induced an internal bias field for the thin samples, which is considered the origin of the large 109.5° domain size in the surface layer by applying the clamping pressure on the domains within that layer. This unexplored mechanism could contribute to solving the scaling effect problem in PMN–28PT single crystals for high-frequency ultrasound biomicroscope applications.