CRYSTALLIZATION AND PROPERTIES OF A PEROVSKITE GLASS-CERAMIC

Crystallization and properties of a PbO-BaO-TiO2-Al2O3-SiO2-B2O3 glass -ceramic were studied. The primary crystalline phase was bulk-crystall ized perovskite titanate. The secondary crystalline phases were a bulk -crystallized transient PbTi3O7 phase and a surface-crystallized PbO . Al2O3 . 2SiO(2) phase. As the heating temperature/time increased, the structure of the precipitated perovskite crystals was transformed fro m cubic to tetragonal, and the measured c/a ratio increased to approac h a constant value which is lower than that for the strain-free crysta l. Moreover, the crystallized amount of perovskite phase first increas ed to a maximum, then decreased. The results have been explained by a coarsening process of the perovskite particles. With increasing freque ncy (200-10(5) Hz), the dielectric constant of the crystallized sample s ranged from about 80-70. The dielectric constant was mainly determin ed by the perovskite content.