To complement the ferroelectric hysteresis measurements, displacement of the samples was measured and resulting strain values are shown in Figs. 7(a-d), together with the hysteresis loops obtained in the simultaneous measurement. For all samples, butterfly shaped strain loops are observed; slightly reaching negative values, indicating normal ferroelectric behavior [34]. Maximum strain of 0.05 % at around 50 kV/cm was obtained again for the BT2 sample at around 50 kV/cm, consistent with its relatively large ferroelectric polarization and dielectric constant among other samples in this study.