In situ observations of the domain evolution and the polarization rotation under bipolar cyclic and static electric fields are carried out for [001]-oriented $68\text{Pb}\left({\text{Mg}}_{1/3}{\text{Nb}}_{2/3}\right){\text{O}}_3\text{−}32{\text{PbTiO}}_3$ (PMN-32PT) single crystal which is located at the morphotropic phase boundary (MPB). The results demonstrate that after being poled in [001] direction, the original rhombohedral $\left(R\right)$ phase is transformed into a monoclinic $M_C$ phase with $Pm$ space group. When the single crystal is subjected to bipolar cyclic electric field, distinct domain-boundary structures are revealed which are unlikely to be detected in static electric loadings. The existence of $R$ phase is also detected during the polarization reversal. Under static electric field, polarization rotation from $M_C$ to $R$ occurs and, as the field increases, phase transition from $M_C$ to tetragonal $\left(T\right)$ phase takes place. In the vicinity of regions where $M_C\text{−}T$ phase transition takes place, polarization reversal of $M_C$ phase is observed, which is attributed to the local stress field from the strain compatibility between the transitioned area and the nontransitioned area. With the removal of the field, $T$ and $M_C$ phases retain while $R$ phase reverses to $M_C$ phase. The results demonstrate that the energy differences among $M_C$, $R$, and $T$ phases are rather slim. Accordingly, the multiphase coexistence and polarization rotation under both cyclic and static electric loadings might be responsible for the ultrahigh piezoelectric response of the [001]-oriented rhombohedral $\text{Pb}\left({\text{Mg}}_{1/3}{\text{Nb}}_{2/3}\right){\text{O}}_3{\text{-PbTiO}}_3$ single crystals near the MPB.

• Received 20 January 2009

DOI:https://doi.org/10.1103/PhysRevB.79.174118