It is difficult to identify the fer

It is difficult to identify the ferroelectricity based on only the round polarization hysteresis loops; however, the strain hysteresis loops showed a butterfly shape, as shown in Fig. 7.A spontaneous polarization reversal clearly occurred in the HIP-BT samples annealed at 800◦C and the HIP-BT ceramics without annealing, and the coercive fields are high in these ceramics. We contend that this is due to the hard polarization reversal natures in these fine-grained ceramics, the insufficient field application to BT grains including the parts with a lower dielectric constant, or the combination of these factors. In essence, the dynamic electric field-induced strains increased with the increase in annealing or sintering temperatures.