Asymmetric Bonding in Glassy TeO ₂ and the Search for Conjectured Terminal Oxygen

Discovering whether glassy TeO2 resembles any or all of its known crystal phases is important both for expanding the existing models of heavy-metal-containing glasses and for understanding macroscopic properties of Te-containing glasses. The asymmetric coordination environments around Te4+ centers in crystalline α-TeO2 and γ-TeO2 have led to a controversy concerning the nature and classification of the Te–O bond in the glass form and, in particular, whether any of the Te–O bonds could be considered as “terminal”. The present work presents new high-resolution X-ray photoelectron spectroscopic data on oxygen and tellurium in TeO2 along with first-principles calculations to investigate the spectroscopic signatures of the Te–O bonds. We show that a true terminal Te═O bond would have a distinctive spectroscopic signature, different from an oxygen bonded asymmetrically to two tellurium atoms; such a terminal oxygen signature is, in fact, not observed in the TeO2 glass. Our data show that the TeO2 glass structure has indeed some short Te–O bonds, as in γ-TeO2, but that these are not terminal and rather are asymmetrically coordinated, similar to both α-TeO2 and γ-TeO2.