Electric field-induced anomalous structural dynamics of nanodomains in BaTiO₃-based relaxor ferroelectric thin films

Relaxor ferroelectrics (RFEs) exhibit ultra-high piezoresponse and unique frequency-dependent dielectric properties making them an attractive choice for next-generation electronic devices. However, the underlying mechanisms governing the structural evolution and dynamic behavior of polar nanodomains (PNDs) under an applied electric field remain a significant open question. Here, time-resolved X-ray microdiffraction technique with picosecond resolution is utilized to investigate the structural dynamics of PNDs in (111)-oriented Sn-doped BaTiO₃​ (BTS) epitaxial RFE thin films. The findings demonstrate that the polarization of nanodomains rotates towards the out-of-plane direction, leading to modulation of d-spacing values as well as contributing to an ultra-high piezoelectric response. An anomalous polarity dependence in piezoelectric strain is observed, with a higher strain under a negative electric field. The strain response also shows a strong dependence on the pulse width/frequency of the electric field, along with an ultra-high piezoelectric strain of up to 1.2%, outperforming various Pb-based relaxor systems. Our findings reveal an intricate interplay between polarization rotation dynamics and electric field polarity in RFEs. These insights not only redefine our understanding of PND dynamics but also pave the way for the development of sustainable, high-performance Pb-free piezoelectrics, ultra-high energy density capacitors, nanoactuators and ultra-compact electronic devices.