The polarization hysteresis curves were obtained using a modified Sawyer-Tower circuit, while the sample was excited by a high-voltage amplifier (Trek 20/20C). The dielectric measurement was conducted with an AC voltage of 1 V using an impedance analyzer (Novocontrol Alpha-A). d33 measurements were conducted on a Berlincourt meter (Piezotest PM300). All electrical measurements were carried out at room temperature.