Crystallization, microstructure and dielectric properties of PbO-BaO-SrO-Nb2O5-B2O3-SiO2 based glass-ceramics

The crystallization kinetics and phase developments of PbO-BaO-SrO-Nb2O5-B2O3-SiO2 based glass-ceramics have been investigated. Lead strontium barium niobate, (Pb,SrBa)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 as-heated surface and interior of glass-ceramics. Such effects 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 much smaller than that of surface-nucleated crystals. This result facilitated to meet the high energy density capacitor application due to ultra-fine grains (< 60 nm) obtained. The dielectric constant increased from 27 for the as-quenched glass to 200 for a highly crystallized glass-ceramics, which was attributed to a significant volume fraction of PSBN phase.