Direct Observation of Antisite Defects and the Induced Ferroelectricity in Antiferroelectric PbHfO₃

Most recently, antiferroelectric perovskite oxides have attracted much attention due to the high tunability of their antiparallel polar configurations by external conditions, such as electric fields and applied strains, yielding rich physics and exotic properties. In this work, we report the effects of antisite defects on antiferroelectric properties of PbHfO₃ (PHO) thin films and find that the antisite substitution of the Hf atom into the Pb site, that is the Hf_Pb defects, can induce the room-temperature ferroelectricity with a remanent polarization of ∼14.5 μC/cm². The Hf_Pb defects are directly observed by atomic-resolution scanning transmission electron microscopy, showing the changes of lattice parameters, the suppression of antiferroelectric distortion, and the emergence of a ferroelectric polar configuration in the Hf-rich PHO thin film. Further density functional theory simulations exhibit changes in bond lengths in terms of the antisite Hf_Pb defects and give specific off-centering displacements of the Pb cations and the Hf_Pb defects, in which the overall net polarizations are calculated, in agreement with the experimental observations. These results give direct evidence for the creation of ferroelectric polarization by antisite defects and shed light on the exploitation of antiferroelectric-ferroelectric transition for designing functional devices based on the polar materials.