Phase stability and dielectric properties of (1-x)PFW plus xPZN derived from mechanical activation

Mechanical activation of mixed oxides of PbO, Fe2O3 and WO3 did not lead to the formation of nanocrystalline Pb(Fe2/3W1/3)O-3 (PFW) of Perovskite stru cture, although the intermediate pyrochlore and PbWO4 phases were realized. Nanocrystallites of Perovskite structure were observed to form in the mixe d oxides of PbO, Fe2O3, WO3, ZnO and Nb2O5 upon 20 h of mechanical activati on. The amount of Perovskite phase thus formed increases with increasing co ntent of PbO, ZnO and Nb2O5 equivalent to Pb(Zn1/3Nb2/3)O-3 (PZN) in compos ition, although Perovskite Pb(Zn1/3Nb2/3)O-3 cannot be synthesized by the c onventional solid-state reaction. A nanocrystalline powder of predominant P erovskite phase was obtained by adding PbO, ZnO and Nb2O5 equivalent to 0.4 mole Pb(Zn1/3Nb2/3)O-3 into the mixed oxides of Pb(Fe2/3W1/3)O-3. However, the activation-derived Perovskite phase was unstable against thermal treat ment at intermediate temperatures around 500 degrees C. Perovskite phase wa s redeveloped with a further increase in the sintering temperature in the r ange 700-800 degrees C, although the presence of PZN destabilizes the Perov skite structure in sintered PFW. 0.6PFW + 0.4PZN sintered at 850 degrees C demonstrates the behavior of a relaxer ferroelectric and exhibits a dielect ric permittivity of similar to 5900 at 100 Hz and a Curie temperature of 27 degrees C. (C) 2000 Elsevier Science B.V. All rights reserved.