Formation mechanism and relaxor ferroelectric properties of lead lithium iron tungstate ceramics

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Abstract
The formation mechanism and ferroelectric properties of Pb(Li1/4Fe1/4W1/2)O3 prepared by solid-state reaction have been investigated in this study. The formation processes of Pb(Li1/4Fe1/4W1/2)O3 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)O3 from above 650 °C. Through a two-stage calcination (700 °C/quenching-regrinding-710 °C/8 h), a nearly single phase of Pb(Li1/4Fe1/4W1/2)O3 is obtained. This compound exhibits a cubic perovskite structure (α = 8.0113 Å) with a partial ordering arrangement of B-site cations. Above 720 °C, becomes Pb(Li1/4Fe1/4W1/2)O3 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)O3 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 relaxor characteristics of Pb(Li1/4Fe1/4W1/2)O3
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