Comprehensive Structural Study of Glassy and Metastable Crystalline BaTi₂O₅

Abstract

The structures of glassy and metastable crystalline BaTi2O5 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 BaTi2O5 (g-BaTi2O5), simulated by Reverse Monte Carlo (RMC) modeling on diffraction data, shows that extremely distorted TiO5 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 SiO4 polyhedra. In addition, XANES measurement revealed that five-coordinated TiO5 polyhedra were formable in the crystallized metastable α- and β-BaTi2O5 phases. The structure of metastable β-BaTi2O5 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.