How different is mechanical activation from thermal activation? A case study with PZN and PZN-based relaxors

Using Pb(Zn1/3Nb2/3)O-3 (PZN) and PZN-based relaxer ferroelectrics, we demo nstrate that the solid state reactions triggered by mechanical activation o f mixed oxides can proceed via a completely different route from that in th e conventional solid state reactions, where the process is controlled by on e or more interfacial reactions and diffusions. Nanocrystallites of perovsk ite Pb(Zn1/3Nb2/3)O-3 are formed in a highly activated state of mixed oxide s where a degree of amorphization has taken place, followed by a steady gro wth with increasing degree of mechanical activation. The absence of transit ional pyrochlores, such as the Pb3Nb4O13-type phases which have always been observed in the conventional solid state reactions, and the considerably l ow local temperature at the collision points suggest that the perovskite ph ase occurs via a process involving nucleation and subsequent diffusionless growth. (C) 2000 Elsevier Science B.V. All rights reserved.