The local structure and vibrational properties of BaTi2O5 glass revealed by molecular dynamics simulation

Molecular dynamics simulations have been performed to prepare the structural model of BaTi2O5 glass. The total correlation function obtained from the structural model agreed rather well with both the X-ray and neutron diffraction data. We found distorted 4-, 5-, and 6-coordinated Ti atoms whose distortion increases with coordination number. Furthermore, the distorted polyhedra were connected to each other by corner-, edge-, or face-sharing. Using the optimal structural model, the vibrational density of state was calculated, and the origin of the bands of Raman scattering spectrum was investigated. It was revealed that not only symmetric and antisymmetric vibration in one TiOn polyhedron but also stretching, bending, and rocking motions in Ti-O-Ti linkage contributed to the Raman bands above 600 cm(-1), which govern the principal vibration in the glass. These results conclude that a Ti-O-Ti network consisting of various types of TiOn polyhedra certainly exists in BaTi2O5 glass, although the local structure around Ti deviates from the Zachariasen's rule of glass formation.