KINETICS OF THE INITIAL-STAGE IN A FIRST-ORDER PHASE-TRANSFORMATION IN THIN-FILMS

The nucleation and growth of islands of a new phase on the surface of solids has been studied both experimentally and theoretically for the particular case of the transition from the pyrochlore to perovskite ph ase in a thin film of a lead zirconate-titanate ferroelectric. This tr ansformation was chosen because the new-phase islands have a stable ci rcular shape in this case, a relatively large size (10(-5)-10(-4) m) p ermitting their observation with an optical microscope, and a low grow th rate (10(-8)-10(-9) m/s). A theoretical analysis of the process, ba sed on the kinetic theory of first-order phase transitions proposed ea rlier, has been carried out and the behavior in time of all main chara cteristics of a phase transformation, namely, nucleation rate, concent ration of the new-phase islands, their size distribution, and relative overheating, has been calculated. The same characteristics have been measured experimentally, thus permitting one for the first time to mak e a thorough comparison of the theoretical with experimental data on t he kinetics of first-order phase transitions. They have been found to be in a good agreement. (C) 1997 American Institute of Physics.