Direct Observation of Polarization Rotation in the Monoclinic M_B Phase under Electrical Loading

The monoclinic phase has received a lot of research because of its importance in explaining the origin of high piezoelectric and ferroelectric performances around the morphotropic phase boundary. In the present study, we have investigated the detailed structural evolution in monoclinic PbZr_0.535Ti_0.465O₃ ferroelectric ceramics induced by an electric field with in situ high-energy synchrotron diffraction combined with two-dimensional (2D) geometry scattering technology. It has been discovered that an electric-field-induced single monoclinic M_B phase persists indefinitely. The lattice, unit cell volume, and spontaneous polarization of the monoclinic M_B structure exhibit significant and flexible responses to the external electric field, i.e., the spontaneous polarization rotates continuously and the lattice and unit cell volume present a butterfly form under the influence of the bipolar electric field. Particularly, direct experimental evidence demonstrates that the macropolarization of PbZr_0.535Ti_0.465O₃ is derived from the spontaneous polarization rotation rather than domain switching, and its volume expansion plays a vital role in the piezoelectric response.