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.

The optical and vibrational properties of BaTi2O5 glass prepared by containerless processing were investigated. The refractive index was 2.15 and the Abbe number was 21.5, as measured by the focal method. The glass was transparent from 340 nm to 7.7 μm. From the Raman scattering spectrum, the maximum phonon energy was found to be 829 cm−1. Using these data, fundamental optical parameters such as the optical basicity, the average oscillator strength, and the optical band gap were estimated. These parameters suggest that BaTi2O5 glass is an attractive material with many potential applications such as lenses, windows, nonlinear optics, and phosphors; moreover, these parameters can guide future development of new titanate glass compositions with superior optical properties.

Local structure origin of higher glass forming ability in Ta doped Co65B35 amorphous alloy J. Appl. Phys. 112, 073520 (2012) NMR and conductivity studies of the mixed glass former effect in lithium borophosphate glasses J. Chem. Phys. 137, 124507 (2012) Robust hydrophobic Fe-based amorphous coating by thermal spraying Appl. Phys. Lett. 101, 121603 (2012) Correlating local structure with inhomogeneous elastic deformation in a metallic glass A high refractive index of 2.231Ϯ 0.001 at 1313 nm is achieved in a colorless, transparent spherical La 4 Ti 9 O 24 glass that was prepared by using an aerodynamic levitation furnace. We also investigate the origin of the high refractive index based on the Lines theory. The physical parameters necessary for the theoretical calculations are the averaged nearest-neighbor Ti-O and La-O distances that are deduced by neutron and synchrotron x-ray diffraction measurement and the partial molar volumes of TiO 2 and LaO 1.5 in the glass. The sum of the calculated TiO 2 and LaO 1.5 susceptibilities provides a La 4 Ti 9 O 24 glass refractive index of 2.244. This is very close to the experimental refractive index of the glass. In addition, the theoretical calculation results suggest that the oxygen fivefold Ti ͑TiO 5 ͒ cluster produces greater susceptibilities than the sixfold Ti ͑TiO 6 ͒ cluster in the glass.

Glass spheres of 2 mm diameter of the title compound are prepared from mixtures of BaTiO3 and TiO2 powders by containerless processing in an aerodynamic levitation furnace (200 MPa, 1427 K, 10 h). The samples are characterized by high-energy XRD. There are three successive phase transitions above the glass transition temperature of 972 K. At 994 K, the permittivity jumps instantaneously by more than one order of magnitude, reaching a peak of 1.4·10 7 . This phenomenon has important implications for obtaining an excellent dielectric glass-ceramic through controlled crystallization of BaTi2O5 glass. It is believed that bulk BaTi2O5 glass will become an important source for fundamental physics study and for practical applications. -(YU*, J.; ARAI, Y.; MASAKI, T.; ISHIKAWA, T.; YODA, S.; KOHARA, S.; TANIGUCHI, H.; ITOH, M.; KUROIWA, Y.; Chem. Mater. 18 (2006) 8, 2169-2173; ISS Sci. Proj. Off., Japan Aerosp. Explor. Agency, Tsukuba, Ibaraki 305, Japan; Eng.) -W. Pewestorf 28-011

TiO2‐based high‐refractive‐index glasses without any network former oxides were fabricated by containerless processing in an aerodynamic levitation furnace. The glass‐forming region of a BaO‐LaO3/2‐TiO2 ternary system was determined. Moreover, the glass transition and crystallization temperatures of a (La1−xBax)4Ti9O24 glass system and a LaO3/2‐TiO2‐M Ox ternary system (M = Ga, Y, Gd, Hf, W, Zn Ge, Nb, Ta, Bi, and Ba) were obtained. Finally, the refractive index dispersion of LaO3/2‐TiO2‐M Ox (M = Ga, W, and Gd) was also investigated. The results indicate that these glasses are promising materials for future optical applications in the visible region. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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