Emergence of isotropy at morphotropic phase boundary of relaxor ferroelectrics
The relaxor ferroelectric materials have received attention because of their gigantic piezoelectric coefficients and are utilized for high-performance electromechanical devices. The physics underlying its functionality, however, is not yet fully understood because of its complex nature such as microscopic heterogeneity and path dependence characteristics. We explored the subdomain structure of the PIN-PMN-PT single crystal sample by the angle-resolved resonance-tracking lateral PFM technique. Inhomogeneous polarization field distribution is observed inside the poled domain forming polar slush structures. Our simulation model suggests that the stoichiometric inhomogeneity at the atomic scale may generate the polar slush structure. Moreover, the simulation study predicts a window near the morphotropic phase boundary between tetragonal and rhombohedral phases that the polarization response becomes isotropic. It is also predicted by Landau theory that the linear combination of the free energy formula of tetragonal and rhombohedral phases can have an isotropic Mexican hat shape with respect to the ferroelectric polarization. It implies the system can be poled along an arbitrary orientation on the macroscopic scale. This study may shed a light on understanding why the best properties of relaxor ferroelectric materials are found at morphotropic phase boundaries.
Host : Prof. Tae Won Noh