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

Abstract

Mechanical activation of mixed oxides of PbO, Fe2O3 and WO3 did not lead to the formation of nanocrystalline Pb(Fe2/3W1/3)O3 (PFW) of Perovskite structure, although the intermediate pyrochlore and PbWO4 phases were realized. Nanocrystallites of Perovskite structure were observed to form in the mixed oxides of PbO, Fe2O3, WO3, ZnO and Nb2O5 upon 20 h of mechanical activation. The amount of Perovskite phase thus formed increases with increasing content of PbO, ZnO and Nb2O5 equivalent to Pb(Zn1/3Nb2/3)O3 (PZN) in composition, although Perovskite Pb(Zn1/3Nb2/3)O3 cannot be synthesized by the conventional solid-state reaction. A nanocrystalline powder of predominant Perovskite phase was obtained by adding PbO, ZnO and Nb2O5 equivalent to 0.4 mole Pb(Zn1/3Nb2/3)O3 into the mixed oxides of Pb(Fe2/3W1/3)O3. However, the activation-derived Perovskite phase was unstable against thermal treatment at intermediate temperatures around 500 °C. Perovskite phase was redeveloped with a further increase in the sintering temperature in the range 700-800 °C, although the presence of PZN destabilizes the Perovskite structure in sintered PFW. 0.6PFW+0.4PZN sintered at 850 °C demonstrates the behavior of a relaxor ferroelectric and exhibits a dielectric permittivity of approximately 5900 at 100 Hz and a Curie temperature of 27 °C.