Defect-driven pinching of hysteretic characteristics in Bi_1/2Na_1/2TiO₃-based ferroelectric thin films

Disorders in ferroelectric thin films highly affect local polarization switching and linked hysteresis behaviors. In this work, we demonstrate line dislocation effects on ferroelectric hysteresis in epitaxial lead-free ferroelectric Bi_1/2(Na_0.82K_0.18)_1/2TiO₃ (BNKT) thin films. To accomplish this, we prepare epitaxial BNKT thin films at low and high growth temperatures using pulsed laser deposition. BNKT thin films grown at low temperatures show dominant single c-domains corresponding to a single hysteresis loop. By contrast, BNKT thin films grown at high temperatures show additional a-domains and a pinched hysteresis loop differently from a single hysteresis loop. Local BNKT lattices have A-site cation deficiency due to local Bi elements being volatile at high growth temperatures. A-site deficient BNKT lattices gain unit-cell-volume shrinkage and form a-domains through accommodating in-plane tensile strains. Theoretical results by phase-field simulation show ferroelectric 90° domain wall pinning leading to double hysteresis characteristics at defect sites with screw dislocation. More details of our work will be presented in the coming on-site conference.