Macroscopic and Nanoscopic Polarization Relaxation Kinetics in Lead-Free Relaxors Bi1/2Na1/2TiO3–Bi1/2K1/2TiO3–BiZn1/2Ti1/2O3

The stability of the field-induced ferroelectric (FE) state was studied in relaxor lead-free ceramics (1 − y)[0.81Bi1/2Na1/2TiO3–0.19Bi1/2K1/2TiO3]–yBiZn1/2Ti1/2O3 both macroscopically and microscopically. A strong dc electric field results in the formation of a stable FE state with a large piezoelectric coefficient for compositions with a small amount of Bi(Zn1/2Ti1/2)O3, which are in the non-ergodic relaxor state at room temperature. Increasing temperature promotes ergodic relaxor behavior, which is accompanied by the rapid destabilization of the induced state, that is, small relaxation times. Based on the obtained data, it is proposed that the depolarization is a two-step process consisting of an initial realignment of the FE domains and their subsequent breakup into polar nanoregions. The ergodic relaxor behavior is also promoted by increasing the Bi(Zn1/2Ti1/2)O3 content. The related charge disorder results in an enhancement of random electric fields and consequently a stable FE state cannot be induced even at room temperature.