Elastic responses to different electric-field directions in relaxor ferroelectric Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 single crystals

Micro-Brillouin scattering was applied to relaxor-based complex perovskite Pb[(Zn1/3Nb2/3)(0.91)Ti-0.09]O-3 (PZN-9% PT) single crystals during a polarization switching under two different electric-field directions along <111> and <101>. Brillouin spectra consisted of one longitudinal and two transverse acoustic modes, and the Brillouin shift and the full width at half maximum of these modes showed clear changes near the coercive field (E-c) where the polarization reversal occurred. In particular, the lowest transverse mode was the most sensitive to E-c. In the case of <111>-poled crystals the Brillouin spectrum exhibited an asymmetric shape in a narrow electric-field range near E-c due to a coupling between the lowest transverse mode and a central peak. In the case of <101>-poled crystals, the lowest transverse mode showed an abrupt softening at E-c and a slow recovery to the initial value upon further increasing the electric field. This may indicate the appearance of the monoclinic symmetry where the polarization can rotate freely toward the orthorhombic phase in the M-B plane under the electric field along the <101> direction. The observation of no changes in the Brillouin spectra with decreasing the electric field seems to indicate that the PZN-9% PT crystal, poled under the field along <101>, does not become rhombohedral, but remains in the induced orthorhombic phase upon the removal of the field. (C) 2003 American Institute of Physics.