The quenched state with dominant shear vibration mode originated from domain reconfiguration in [001]-oriented Pb(Mg_1/3Nb _2/3)O₃-PbTiO₃ single crystals

We present results of investigations into a low-frequency vibration mode (LVM) in [001] poled Pb(Mg_1/3Nb_2/3)O₃- PbTiO₃ crystal. Through a series of impedance measurement and polarization microscopy observations of domain structure, we find that the LVM is a shear mode arising from a polarization component lying in the (001) plane. Through quenching, a metastable state can be reached where the LVM is greatly enhanced and the thickness vibration mode of the typical poled state is highly suppressed. Measurements on the transverse vibration modes of differently oriented crystal samples show that the LVM state possesses a macroscopic orthorhombic symmetry (mm2) with its polarization vector along the [110] direction. The structural differences between the LVM-enhanced state and the usual poled state are discussed in detail. The two states have the same crystalline phase but different ferroelectric domain structures. When heated above the rhombohedral-to-tetragonal transition temperature, T_rt, a tetragonal phase with (110) domain walls is formed. This domain structure can be frozen by the rapid quenching through the T_rt. Based on compatibility of ferroelectric polarizations at domain walls, and observed polarization microscopy results, we are able to infer the possible arrangement of domain structures in rhombohedral and tetragonal phases. The [110] polarization component associated with LVM originates from the domain structure with well-organized (110) domain walls.