Understanding the depolarization temperature in (Bi0.5Na0.5)TiO3-based ferroelectrics

Depolarization temperature, or Td, in ferroelectric materials limits the high temperature operation regime as the long range dipolar ordering could not be maintained beyond Td during zero field heating. Therefore, the control of Td has been always drawing the attention of the ferroelectric/piezoelectric community. Some particular issues include: Which point defect is more responsible for the change of Td? What is the phase equilibrium as a function of Td? In this paper, our goal is to elaborate the correlation between Td and defect chemistry in 85% (Bi0.5Na0.5)TiO3-15% BaTiO3 (BNT-15BT) ferroelectric ceramics. Various experimental tools are employed and cross referenced, including dielectric measurements, thermal stimulated depolarization current, impedance spectroscopy, scanning transmission electron microscopy and in-situ transmission electron microscopy. Collectively this study generates a more insightful understanding of Td in BNT-based ferroelectrics.