Particle and grain size effects on the dielectric behavior of the relaxor ferroelectric Pb(Mg_1/3Nb_2/3)O₃

Abstract

The role of particle and grain size on the dielectric behavior of the perovskite relaxor ferroelectric Pb(Mg_1/3Nb_2/3)O₃ [PMN] was investigated. Ultrafine powders of PMN were prepared using a reactive calcination process. Reactive calcination, the process by which morphological changes take place upon reaction of the component powders, produced particle agglomerates less than 0.5 μm. Through milling, these structures were readily broken down to ∼70 nanometer-sized particulates. The highly reactive powders allowed densification as low as 900 °C, but with corresponding grain growth in the micron range. Such grain growth was associated with liquid phase sintering as a result of PbO–Nb₂O₅ second phase(s) pyrochlore. Sintering, assisted by hot uniaxial pressing, below the temperature of liquid formation of 835 °C, allowed the fabrication of highly dense materials with a grain size less than 0.3 μm. The dielectric and related properties were determined for samples having grain sizes in the range of 0.3 μm to 6 μm. Characteristic of relaxors, frequency dependence (K and loss) and point of T _max were found to be related to grain and/or particle size and secondarily to the processing conditions. Modeling of particle size/dielectric behavior was performed using various dielectric properties of 0–3 composites comprised of varying size powder in a polymer matrix. An intrinsic-microdomain perturbation concept was proposed to interpret observed scaling effects of the relaxor dielectric behavior in contrast to normally accepted extrinsic grain boundary models.