Irreversible Phase Transitions in BiFeO3 -SrTiO3 Lead-Free Piezoceramics

Abstract

The development of high-performance lead-free piezoelectric materials has gained significant attention due to environmental concerns regarding lead toxicity. In this study, through in-situ poling synchrotron X-ray diffraction (XRD), dielectric spectroscopy, and ferroelectric measurements, we demonstrate an irreversible transition from non-ergodic relaxor behaviour to long-range ferroelectric ordering under applied electric fields in (1-x)BiFeO₃ -xSrTiO₃ with MnO₂ addition (BF-ST-Mn).The optimal composition with x = 0.44 exhibits electrostrain of ~0.10% at 80 kV cm -1 through irreversible pseudo-cubic to rhombohedral structural transformation followed by ferroelectric domain switching. Unlike BF-ST-Nb systems that maintain pseudo-cubic symmetry, the BF-ST-Mn undergo irreversible phase transitions. Synchrotron XRD reveals initial structural transformation during the first electrical cycle, followed by domain switching in subsequent cycles. It provides promising pathways for lead-free actuator applications requiring high electrostrain at moderate driving fields.