Microstructure at morphotropic phase boundary in Pb(Mg _1/3Nb _2/3)O ₃-PbTiO ₃ ceramic: Coexistence of nano-scaled {110}-type rhombohedral twin and {110}-type tetragonal twin

For more than half a century, the morphotropic phase boundary (MPB) has drawn constant interest in developing piezoelectric materials, as the phase instability at the region significantly enhances piezoelectricity. However, the local structure/symmetry at the MPB region is still under controversy. The investigation on morphology and origin of the local structure at MPB is of considerable importance to provide a microstructure basis for high piezoelectricity. In the present study, we thus use high resolution transmission electron microscopy to investigate the microstructure feature of MPB at PMN-PT ceramics. The local structure is shown to be the coexistence of nano-scaled {110}-type rhombohedral (R) twin and {110}-type tetragonal (T) twin. Such nano-scaled coexistence can be due to a nearly vanishing polarization anisotropy and low domain wall energy at MPB, which thus facilitates polarization rotation between 001 _T and 111 _R states and leads to high properties of MPB compositions.