  Consecutive stochastic 90{\deg} polarization switching events, clearly
resolved in recent experiments, are described by a new nucleation and growth
multi-step model. It extends the classical Kolmogorov-Avrami-Ishibashi approach
and includes possible consecutive 90{\deg}- and parallel 180{\deg}-switching
events. The model predicts the results of simultaneous time-resolved
macroscopic measurements of polarization and strain, performed on a tetragonal
Pb(Zr,Ti)O3 ceramic in a wide range of electric fields over a time domain of
five orders of the magnitude. It allows the determination of the fractions of
individual switching processes, their characteristic switching times,
activation fields, and respective Avrami indices.
