Domain Dynamics and Local Level Switching Behaviors of Sol–Gel Nanopowder-Derived Lead-Free Piezoelectric Bi_0.5(Na_0.78K_0.22)_0.5TiO₃ Ceramics

The material properties of sol–gel nanopowder-derived lead-free Bi_0.5(Na_0.78K_0.22)_0.5TiO₃ (BNKT) ceramics are systematically investigated for high-response piezoelectric device applications. To elucidate the principle of the domain dynamics and local level ferroelectric switching behaviors of environmentally friendly BNKT ceramics, we systematically analyze the Rayleigh parameters and the first-order reversal curve (FORC) of the BNKT ceramics and compare the results with those of the standard measurement method. Based on the characterization of Rayleigh parameters, it is clarified that the contribution of the domain-wall motion of the sol–gel-derived BNKT ceramics is higher than that of solid-state reaction-derived ceramics. We also analyze the FORC distribution diagram-associated hysteron density functions for visualizing reversible and irreversible contributions of domain walls and switching behaviors above the Rayleigh regime. The switching behaviors are explained by considering the defects and microstructural differences of the BNKT ceramics, which are affected by both reversible and irreversible contributions. The sol–gel-derived BNKT ceramics show highly localized and well-defined FORC distribution diagrams with the sharp maximum of the irreversible component and the low reversible contribution, which clearly indicate more homogeneous switching properties and less defects than solid-state reaction-derived ceramics because each switching unit gives almost identical contributions to the total polarization. In this study, the developed technique and gained information are used to explore a fundamental understanding of the domain dynamics and local level switching behaviors of lead-free piezoelectric ceramics. We believe that our investigation certainly positions itself in various multifunctional electronic applications without using toxic lead-based piezoelectrics.