Having pioneered mechanical activation on Pb-based relaxor ferroelectrics, we describe a unique order-disorder transformation phenomenon brought about by mechanical activation in Pb-based relaxor ferroelectrics of complex perovskite. B-site disorder in Pb(Sc1/2Ta1/2)O-3 (PST) which is traditionally tailored by thermal annealing after sintering at elevated temperatures, can be triggered by mechanical activation. The B-site disorder in Pb(Sc1/2Ta1/2)O-3 triggered by mechanical activation can well be retained in sintered Pb(Sc1/2Ta1/2)O-3, leading to an unique ferroelectric transition behavior (e.g., from a normal ferroelectric to relaxor) and a shift in the Curie temperature. (C) 2004 Kluwer Academic Publishers.