Depolarization field in relaxor-based ferroelectric single crystals under one-cycle bipolar pulse drive*

Abstract

The [001] c -polarized (1 − x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN−PT) single crystals are widely used in ultrasonic detection transducers and underwater acoustic sensors. However, the relatively small coercive field (∼ 2 kV/cm) of such crystals restricts their application at high frequencies because the driving field will exceed the coercive field. The depolarization field can be considerably larger in an antiparallel direction than in a parallel direction with respect to polarization when the bipolar driving cycle starts. Thus, if the direction of the sine wave signal in the first half cycle is opposite to the polarization direction, then the depolarized domains can be repolarized in the second half of the sine cycle. However, if the direction of the sine wave signal in the first half of the cycle is along the polarization direction, then the change is negligible, and the domains switched in the second half of the sine cycle cannot be recovered. The design of electric driving method needs to allow the use of a large applied field to emit strong enough signals and produce good images. This phenomenon combined with the coercive field increases with the driving frequency, thereby making the PMN−PT single crystals usable for high-frequency applications. As such, the applied field can be considerably larger than the conventionally defined coercive field.