Electric-field-induced phase transitions in rhombohedral Pb(Zn1/3Nb2/3)1-xTixO3

High-energy x-ray-diffraction experiments performed on rhombohedral Pb(Zn1/3Nb2/3)12xTixO3 (PZN-x%PT) crystals with x=4.5% and 8% show that an electric field applied along the [001] direction induces the tetragonal phase, as earlier proposed. Our experiments reveal that in PZN-4.5%PT such a phase change occurs via a third phase with monoclinic symmetry MA, which is observed at intermediate field values. This is in agreement with first-principles calculations predicting the rotation of the polarization between the rhombohedral and tetragonal phases in this material. A different polarization path between the rhombohedral and tetragonal phases, through a second monoclinic phase MC, has been previously reported in PZN-8%PT. The microscopic characterization of these crystals allows us to explain the ultrahigh macroscopic strain observed in PZN-x%PT under an electric field. Furthermore, some unusual scattering profiles displayed by exceptionally good crystals provide experimental evidence of the high anharmonicities and near degeneracy of the different phases in these extremely deformable materials