BONDING NATURE IN TELLURITE GLASSES

We show that the variation of the structural unit in tellurite glasses is due to the charge transfer from modifier atoms to TeO6 octahedra with use of first-principles molecular-orbital calculations. Mulliken overlap populations indicate that the oxygen coordination number of a Te atom reduces as the charge transfer progresses. This is consistent with the trend found in metal tellurite structures. Orbital-overlap population analysis reveals that the transferred electrons to the Te-O antibonding orbital cause breaking in the Te-O bonds and lead to reducing the coordination number of the Te atom. The bond ionicity and charge states of a Te atom and an O atom in α-TeO2 are also presented. © 1995 The American Physical Society.