Creep behavior of soft and hard PZT ceramics during mechanical loading and unloading

The creep behavior of strain and electrical polarization in two poled PZT with different compositions was investigated during stress loading and unloading. Being different from the standard testing methods, the creep behaviors at all stress levels were characterized using a single sample, rather than a fresh sample at each load level. During loading, the creep of polarization and strain are observed at higher stress than that in soft PZT due to the effect of internal bias field. During unloading, significant recovery of strain and polarization was observed in the hard PZT, demonstrating that a compressive stress of 380 MPa cannot reorient the ordered defect dipoles in Fe doped hard PZT. Two equations P0.5=α1log(t+t0)+β1 and Screep0.5=a2log(t+t0)+β2Screep0.5=a2  log(t+t0)+β2 were summarized to describe the creep polarization and the creep strain, respectively. Compared with the conventional power law creep equations, the two equations can fit the experimental results well in the whole range of stress holding.