Fabrication of BaTi₂O₅ glass-ceramics with unusual dielectric properties during crystallization

A 2-mm-diameter glass sphere of ferroelectric BaTi₂O₅ was fabricated from melt using containerless processing. The glass structure was analyzed by high-energy X-ray diffraction using an incident photon energy of 113.5 keV, indicating that distorted Ti-O polyhedra, with average coordination number (N_Ti-o) of approximately 5, presented in the glass. Above the glass transition temperature (972 K), three successive phase transitions, from glass to a metastable a phase at 972 K, then to a metastable β phase at 1038 K, and finally to a stable monoclinic γ phase above 1100 K, were observed. At the crystallization temperature of the a phase, the permittivity jumped instantaneously by more than 1 order of magnitude, reaching a peak of 1.4 × 107. This interesting phenomenon, occurring near the crystallization temperature, has important technical implications for obtaining an excellent dielectric glass-ceramic through controlled crystallization of BaTi ₂O₅ glass.