Crystallization and Analysis of Perovskite Crystals in Ferroelectric-based Glasses

Abstract

The effects of heat treatment on properties of ferroelectric materials prepared by glass-ceramic route based on two glass compositions with different ratios of glass forming oxides were studied. The compositions were Glass I: 20PbO – 20BaO – 25TiO2– 5Al2O3–15SiO2– 15B2O3(mol%) and Glass II: 20PbO – 20BaO – 25TiO2– 5Al2O3– 5SiO2–25B2O3(mol%). Both glasses were heat treated at 600, 700 and 800oC for 8 h to form glass-ceramics. XRD found PbTiO3 as the primary phase but not BaTiO3 Ferroelectric PbTiO3 .had tetragonal perovskite structure. Increasing heat treatment temperature resulted in an increase of PbTiO3 crystal size with an increase of c/a ratio (>1) which indicates the increase in tetragonality of PbTiO3 phase. XRD also found crystallization of secondary phase(s) in each heat treated glass and analysis by SEM revealed that the phase composition and morphology were different for different glass compositions. The apparent densities of these glass-ceramics were found to increase with increasing heat treatment temperature due to increase amount of crystalline phases. The room temperature dielectric constants of as-annealed glasses were about 20 and increased to values of 30 – 65 for crystallized samples.