Understanding Microstructural Effects on Long Term Electrical Fatigue in Multilayer PZT Actuators

摘要

In this study, multilayered PbZr_xTi_(1-x)O_3 (PZT) samples were produced by tape-casting and subsequent sintering at temperatures in the range of 1175 ℃ to 1325 ℃. Sintering times were 6 minutes and 24 minutes. Samples were poled and also electrically fatigued by long-term exposure ( ≈ 10~6 cycles) to cyclic electric fields. The parameters of initial and remnant polarization were estimated from hysteresis loops. Changes in the crystallographic microstructure as a function of sintering temperature T_S and sintering time were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD) to gain insight on fatigue mechanisms and their prevention. The microstructural results, such as domain reorientation and amount of secondary phases, explained the results of electrical observations. We found that grain sizes and internal strains were major influence factors on device performance. Domain sizes were about two orders of magnitude smaller than grain sizes. Therefore, domain-grain wall interaction did not influence domain switching. Domain wall movement was facilitated in samples processed at T_S less than 1250 ℃, and such samples were more resistant to electrical fatigue. Samples degraded faster at TS above 1250 ℃, but here a higher device performance power was found due to an increased unit cell tetragonality that yielded higher polarization values.