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 α 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 α 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 BaTi2O5 glass.

The structures of glassy and metastable crystalline BaTi 2 O 5 fabricated by the containerless method were comprehensively investigated by combined X-ray and neutron diffractions, XANES analyses, and computer simulations. The three-dimensional atomic structure of glassy BaTi 2 O 5 (g-BaTi 2 O 5 ), simulated by Reverse Monte Carlo (RMC) modeling on diffraction data, shows that extremely distorted TiO 5 polyhedra interconnected with both corner-and edge-shared oxygen formed a higher packing density structure than that of conventional silicate glass linked with only corner-sharing of SiO 4 polyhedra. In addition, XANES measurement revealed that five-coordinated TiO 5 polyhedra were formable in the crystallized metastable R-and -BaTi 2 O 5 phases. The structure of metastable -BaTi 2 O 5 was solved by ab initio calculation, and refined by Rietveld refinement as group Pnma with unit lattices a ) 10.23784(4) Å, b ) 3.92715(1) Å, c ) 10.92757(4) Å. Our results show that the glass-forming ability enhanced by containerless processing, not by "strong glass former", fabricated new bulk oxide glasses with novel structures and properties.