Structural Integration of Tellurium Oxide into Mixed-Network-Former Glasses: Connectivity Distribution in the System NaPO₃–TeO₂

Graphical Abstract

Sodium phosphate tellurite glasses prepared and structurally characterized by XP and NMR spectroscopies, show no new structural units and no sharing of the network modifier. The resulting chemical segregation leads to a nonrandom sodium distribution. The picture shows the fraction of different linkages in a (NaPO₃)_x(TeO₂)_1−x glass.

Abstract

Sodium phosphate tellurite glasses in the system (NaPO₃)_x(TeO₂)_1−x were prepared and structurally characterized by thermal analysis, vibrational spectroscopy, X-ray photoelectron spectroscopy (XPS) and a variety of complementary solid-state nuclear magnetic resonance (NMR) techniques. Unlike the situation in other mixed-network-former glasses, the interaction between the two network formers tellurium oxide and phosphorus oxide produces no new structural units, and no sharing of the network modifier Na₂O takes place. The glass structure can be regarded as a network of interlinked metaphosphate-type P⁽²⁾ tetrahedral and TeO_4/2 antiprismatic units. The combined interpretation of the O 1s XPS data and the ³¹P solid-state NMR spectra presents clear quantitative evidence for a nonstatistical connectivity distribution. Rather, the formation of homoatomic POP and TeOTe linkages is favored over mixed POTe connectivities. As a consequence of this chemical segregation effect, the spatial sodium distribution is not random, as also indicated by a detailed analysis of ³¹P/²³Na rotational echo double-resonance (REDOR) experiments.