An induced state with dominant shear vibration mode originating from domain reconfiguration in [001]-poled PMN-PT single crystals

Abstract

Crystalline relaxor-PT piezoelectrics poled in [001] can sometimes exhibit a second thickness-mode resonance in the impedance spectrum at a frequency lower than the resonance associated with longitudinal vibrations. In this study we investigate this low vibration mode (LVM) in PMN-PT single crystal. We show that the mode is a shear wave mode arising due to a polarization component lying in the (001) plane. The presence of the mode and its strength in the impedance spectrum can be controlled either by thermal quenching from a temperature above the tetragonal-rhombohedral transition temperature or through the application of a bias voltage during slower cooling. By varying the rate of cooling or the applied bias during cooling the impedance spectrum peak corresponding to the LVM can be enhanced in which case the usual longitudinal resonance peak is suppressed or the LVM can be suppressed in which case the longitudinal resonance is enhanced. Samples in which the LVM is enhanced exhibit a macroscopic orthorhombic symmetry (mm2) with a polarization vector lying along the [110] direction as demonstrated by the transverse vibration modes observed in samples cut to different crystallographic orientations. Samples in which the LVM is enhanced exhibit the same phase structure but different domain structures than samples in which it is suppressed. The LVM is characterized by a domain structure with (110) domain walls. These walls appear in the high-temperature tetragonal phase and can be frozen into the room temperature state by rapid quenching. Based on the compatibility of possible polarization directions and domain wall orientations with polarization microscopy observation of our samples, possible arrangements of the domain structures in the rhombohedral and tetragonal phases are determined. It is shown that the [110] polarization component associated with the LVM originates from a domain structure with well-organized (110) domain walls.