Why lanthanum-substituted bismuth titanate becomes fatigue free in a ferroelectric capacitor with platinum electrodes

${\mathrm{Bi}}_{\mathrm{4}}{\mathrm{Ti}}_{\mathrm{3}}{\mathrm{O}}_{\mathrm{12}},$ (BTO) a Bi-layered perovskite oxide, shows fatigue after repeated ferroelectric polarization reversals. On the other hand, ${\mathrm{Bi}}_{\mathrm{3.25}}{\mathrm{La}}_{\mathrm{0.75}}{\mathrm{Ti}}_{\mathrm{3}}{\mathrm{O}}_{\mathrm{12}}$ (BLT) is fatigue free. From an extensive transmission electron microscopy study, it was found that there is a high density of antiphase boundaries (APBs) in BLT like in the fatigue-free ${\mathrm{SrBi}}_{\mathrm{2}}{\mathrm{Ta}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{9}}$ but not in BTO. It is proposed that the existence of APBs possibly plays a key role in the fatigue-free behavior of Bi-layered perovskite oxides.