Fluctuating local polarization: a generic fingerprint for enhanced piezoelectricity in Pb-based and Pb-free perovskite ferroelectrics.

Understanding the atomistic mechanism underlying high piezoelectricity has long been a central focus in research of functional ferroelectric materials. Despite decades of research across various perovskite piezoelectric systems, a clear consensus on the underlying mechanisms remains elusive. We propose a new concept-fluctuating local polarization-a critical factor that effectively correlates with piezoelectricity and could serve as a generic fingerprint for enhanced piezoelectricity. This is achieved by quantitatively capturing the local polarization characteristics of 16 compositions from classical piezoelectric systems. Our findings show that greater fluctuating local polarization, considering both the magnitude and the orientation disorder of local polar displacement vectors, yields improved piezoelectric performance. High fluctuating local polarization value, corresponds to a reduced local potential energy stiffness, thereby facilitating polarization variations and resulting in an amplified piezoelectric response. The concept can further explain the performance gap between Pb-based and Pb-free ferroelectrics arising from the distinct A-site polar displacement characteristics. Overall, our concept offers an atomic-level insight into the enhanced piezoelectricity of perovskites and provides a theoretical framework for designing high-performance piezoelectric materials.