Kinetics of nucleation of thermodynamically ordered ferroelectric phases in PbMg$_{1/3}$Nb$_{2/3}$O$_{3}$–$x$PbTiO$_{3}$ crystals with different compositions

The kinetics of electric field-induced nucleation of ordered ferroelectric phases from a mixed glassy relaxor state has been studied in a number of single-crystal $(1-x)$PbMg$_{1/3}$Nb$_{2/3}$O$_{3}$–$x$PbTiO$_{3}$ (PMN-$x$PT) solid solutions ($x$ = 29, 33, 35%) lying in a morphotropic phase region. It is shown that the formation of these phases and fast establishment of a macroscopic polarization are preceded by some delay time, depending on the electric field strength and temperature. It is found that the monoclinic phase is thermodynamically stable at room temperature in all the compounds in the time ( 3000 s) and electric field ($\sim$1 kV/cm) ranges under study, whereas the monoclinic phase of the compound with $x$ = 35% transforms, at temperatures near the temperature of the morphotropic phase transition after insignificant time interval of $\sim$100 s, to another stable ferroelectric tetragonal phase.