Polarization extension mechanism revealed through dynamic ferroelectric hysteresis and electric field driven structural distortions in lead free Na0.5Bi0.5TiO3 ceramics

The electric field amplitude (E<sub>o</sub>) dependent dynamic ferroelectric hysteresis and polarization current density curves measured at room temperature for Na<sub>0.5</sub>B<sub>i0.5</sub>TiO<sub>3</sub>(NBT), showed three different stages of polarization reversal mechanism. The scaling relationship confirmed the dominance of domain wall motion at stage-I (i.e., upto E<sub>o</sub> <35 kV/cm), followed by domain switching at stage-II (35 kV/cm < E<sub>o</sub> < 60 kV/cm). Interestingly, a unique behaviour with two sub stages were observed in stage-III (60 kV/cm (<E<sub>o</sub> <90 kV/cm), with two distinct switching mechanisms viz., polarization rotation at stage III-A and polarization extension at stage III-B. X-ray diffraction analysis based on the Rietveld refined atomic positional co-ordinates, in electrically poled system strongly favors the polarization extension mechansim proposed at stage III-B. The measured E<sub>o</sub>-dependent longitudinal piezoelectric response (d<sub>33</sub> and g<sub>33</sub>) values match closely with our proposed polarization reversal mechanism