Unipolar fatigue of ferroelectric lead–zirconate–titanate

In multilayer actuators the ferroelectric material is known to degrade under bipolar and to some degree under unipolar electric loading. Fatigue effects due to unipolar cycling of a commercial bulk lead–zirconate–titanate up to 4·108 cycles at 2 Ec are demonstrated. Unipolar as well as bipolar polarisation and strain hysteresis loops are measured after fatigue. Bipolar measurements after cycling show a small decrease of the remnant polarisation and an increasing asymmetry of the strain hysteresis with cycle number, which is explained by an offset polarisation. This offset polarisation is reduced under application of bipolar fields. A small offset-field is also observed. Etch grooves known to occur after bipolar fatigue are not found after unipolar fatigue. The results reveal that different mechanisms are responsible for bipolar and unipolar fatigue.