Electric field effects on the phase transitions in [001]-oriented (1-x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ single crystals with compositions near the morphotropic phase boundary

Dielectric behavior and phase transitions of [001] oriented (1-x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ single crystals with x=29, 31, 32, and 33 % were investigated by impedance measurements and high resolution x-ray diffraction analysis under various electrical and thermal conditions. Application of a bias field along [001] can shift down the Rhombohedral-Tetragonal structural phase transition, so that the morphotropic phase boundary is shifted by the bias field. We have quantified this shift under 1 kV dc bias along [001]. A transition between the normal ferroelectric and relaxor states was indicated by the appearance of a frequency dispersion shoulder slightly below T_C and an abrupt disappearance of the frequency dispersion at a lower temperature. This relaxor-ferroelectric transition was found to be thermally driven in the compositions with PbTiO₃ (PT) contents from 31 to 33 %. While for the composition with 29% PT content, a bias field can help to produce this transition.