Crystallization and dielectric properties of borate-based ferroelectric PbTiO3 glass-ceramics

Bulk crystallized PbTiO3 (PT) was the major crystalline phase in borate-based glass ceramics with starting composition 39PbO–1BaO–25TiO2–9.8Al2O3–1SiO2–24.2B2O3 (mol%). Crystallization of PT starts at ≥520 °C and the crystal size and c/a ratio of PT were approximately the same for all samples heat treated between 520 and 700 °C. Two transient unidentified phases were induced when crystallized between 520 and 650 °C. The first at 520 °C followed by a second at 550 °C. At >650 °C, PbTi3O7 was present in addition to PbTiO3. The electrical properties of glasses heat treated between 550–700 °C were investigated by fixed frequency capacitance measurements and impedance spectroscopy, IS. No permittivity maximum or Curie temperature, Tc, for the PT phase was observed from fixed frequency capacitance measurements for glasses heat treated below 700 °C, however IS data analysis using electric modulus (M″) spectroscopy revealed the PT phase to have Tc ∼480 and 440 °C for samples heat treated at ∼550 and 700 °C, respectively. The conductivity of the PT phase and the dc conductivity of the glass heat treated at 700 °C were significantly higher than those of glasses heat treated at lower temperatures suggesting there is significant compositional differences between the glass heat treated at 700 °C compared to those treated at ≤650 °C.