Stress release-induced piezoresponse in lead-free piezoceramics with high-symmetry morphotropic phase boundary

The (1 − x)(Bi0.5Na0.5)TiO3-xBaTiO3 (BNT-BT) system has attracted a great deal of interest because it presents a morphotropic phase boundary (MPB) between the rhombohedral and tetragonal phases for 0.05 < x < 0.08. Identifying the MPB in the BNT-BT system often results in materials exhibiting a high-symmetry (pseudo)cubic x-ray diffraction pattern. However, this singular composition exhibits ferroelectricity, which has been explained as a consequence of a field-induce phase transformation. Here, we demonstrate that the stress release after poling, from the virgin state of the sample, is a crucial phenomenon to obtain piezoelectric response in MPB BNT-BT. The mechanism behind the unusual poling–depoling process in piezoceramics exhibiting high-symmetry MPB is elucidated by combining x-ray diffraction measurements and advanced Raman spectroscopy. This underscores the importance of post-poling stress release from the virgin state as a critical factor in attaining piezoelectric response in lead-free piezoceramics with high-symmetry MPB configurations.