FORMATION MECHANISM AND RELAXOR FERROELECTRIC PROPERTIES OF LEAD LITHIUM IRON TUNGSTATE CERAMICS

The formation mechanism and ferroelectric properties of Pb(Li1/4Fe1/4W1/2)O-3 prepared by solid-state reaction have been investigated in this study. The formation processes of Pb(Li1/4Fe1/4W1/2)O-3 are characterized to be an initial reaction of lead tungstates PbWO4 and Pb2WO5 at a low temperature range, followed by a subsequent reaction to produce Pb(Li1/4Fe1/4W1/2)O-3 from above 650 degrees C. Through a two-stage calcination (700 degrees C/quenching-regrinding-710 degrees C/8 h), a nearly single phase of Pb(Li1/4Fe1/4W1/2)O-3 is obtained. This compound exhibits a cubic perovskite structure (a = 8.0113 Angstrom) with a partial ordering arrangement of B-site cations. Above 720 degrees C, Pb(Li1/4Fe1/4W1/2)O-3 becomes thermodynamically unstable and gradually decomposes in forming elongated Pb2WO5 grains, thereby resulting in a nonhomogeneous microstructure. As the ac frequency increases, the maximum dielectric permittivity of Pb(Li1/4Fe1/4W1/2)O-3 significantly decreases; in addition, the corresponding temperature increases. The strong frequency dependence of dielectric properties, as well as the critical exponent and diffuseness evaluated through a modified permittivity-temperature equation proposed in this study, verify the relaxer characteristics of Pb(Li1/4Fe1/4W1/2)O-3.