Behavior of indium oxide in zinc phosphate and borophosphate glasses

The effect of indium oxide on the structure and properties of zinc phosphate and zinc borophosphate glasses has been investigated in the series (50?x)ZnO–xIn₂O₃–50P₂O₅ and 30ZnO–(20?x)B₂O₃–xIn₂O₃–50P₂O₅ with x = 0–20 mol% In₂O₃ in both series. Their physical properties were measured, and their structure was studied by Raman and NMR spectroscopy. Glass transition temperature in the phosphate glass series increases with increasing In₂O₃ content as well as their chemical durability. The observed changes in the ³¹P MAS NMR spectra with increasing In₂O₃ content revealed the depolymerization of phosphate chains due to the replacement of ZnO by In₂O₃ resulting in an increase in the O/P ratio in the glass structure. ¹¹B MAS NMR spectra revealed the presence of BO₄ units in the glass structure in the borophosphate glass series; these spectra give no evidence for the formation of B–O–In bonds. Their glass transition temperature slightly decreases with increasing In₂O₃ content. The values of the molar volume in these glasses do not change substantially when B₂O₃ is replaced by In₂O₃. This can be ascribed not only to differences in boron (BO₄) and indium (InO₆) coordination, but also to a higher ionicity of In···O bonds in comparison with B–O bonds. The obtained data resulted in the conclusion that indium oxide behaves as a modifying oxide in both glasses.