Electric-field induced phase transition and fatigue behaviors of (Bi_0.5+x/2Na_0.5-x/2)_0.94Ba_0.06Ti_{1- x}Fe_xO₃ ferroelectrics

The dielectric, piezoelectric properties, and fatigue behaviors of stoichiometric (Bi_0.5+x/2Na_0.5-x/2)_0.94Ba_0.06Ti_{1- x}Fe_xO₃ (BNBT-xFe) ferroelectrics are investigated. Fe substitution leads to the downward shift of the ferroelectric-relaxor transition temperature (T_{F -R}) and increase in strain. Meanwhile, fatigue behaviors of the modified ceramics are significantly enhanced. Ex situ X-ray diffraction and transmission electron microscopy reveal microscopic mechanism for polarization fatigue on different compositions. The fatigue-free behavior of ferroelectric BNBT-0.03Fe is not only attributed to a mechanism involving the formation of defect dipoles, which reduces the pinning effect of migratory oxygen vacancies on domain walls, but is also connected to the decrease in easily suppressed field-induced ferroelectric tetragonal phase. While for ergodic relaxor BNBT-0.09Fe, the absence of domain wall contributes to the good fatigue resistance behavior. Interestingly, electric cycling results in an increased fraction of relaxor phase, accompanying by the increase in the total strain and decrease in remnant polarizations.