Orientation dependence and electric-field effect in the relaxor-based ferroelectric crystal (PbMg1/3Nb2/3O3)0.68(PbTiO3)0.32

Abstract

Dielectric permittivities, polarization–electric-field hysteresis loops, and domain structures have been measured as a function of temperature in relaxor-based ferroelectric single crystals (PbMg1/3Nb2/3O3)0.68(PbTiO3)0.32 (PMN-32%PT) for ⟨110⟩cub and ⟨211⟩cub orientations. Contrary to the pure PbMg1/3Nb2/3O3 (PMN), PMN-32%PT exhibits apparent crystallographic orientation dependences of dielectric permittivities, polarizations, domain structures and phase transitions. With a prior field-cooled treatment, a field-induced state, perhaps of orthorhombic symmetry, is evidenced and coexists with the rhombohedral symmetry in the low-temperature region. This field-induced phase is manifested by an extra dielectric peak observed near 373 K for the ⟨211⟩cub orientation. A relaxation mechanism which is responsible for the so-called diffuse phase transition crosses a wide temperature region of ∼340–400 K and results from fluctuations between rhombohedral and tetragonal states. In order of increasing temperature (without a prior field-cooled treatment), PMN-32%PT undergoes successive phase transformations: rhombohedral phase→coexistence of rhombohedral and tetragonal phases→tetragonal phase→coexistence of tetragonal and cubic phases→cubic phase.