Crystallization kinetics and dielectric properties of nanocrystalline lead strontium barium niobates

The crystallization kinetics and phase developments of PbO-BaO-SrO-Nb₂O₅-B₂ O₃-SiO₂-based glass-ceramics was investigated. Lead strontium barium niobate, (Pb,Sr,Ba)Nb₂O₆, with a tetragonal tungsten-bronze structure formed as the major crystalline phase, which showed evidence of both surface and bulk crystallization. The results of the present study showed significant evidence of a change in crystallization mechanism between the as-heated surface and the interior of glass-ceramics. This effect could be attributed to a volatilization of PbO taken place readily on the surface region of sample during heating. The grain size of the bulk-nucleated (Pb,Sr,Ba)Nb₂O₆ crystals was substantially smaller than that of surface-nucleated crystals. This result facilitated meeting the capacitors as high energy density application due to the ultrafine grains (<60 nm) obtained. The dielectric constant increased from 27 for the as-quenched glass to 200 for a highly crystallized glass-ceramic, which was attributed to a significant volume fraction of (Pb, Sr, Ba)Nb₂O₆ phase.