Role of titanium in sodium titanophosphate glasses and a model of structural units

摘要

Glasses with composition 50Na(2)O-xTiO(2)-(50-x)P2O5(0 less than or equal to x less than or equal to 15) have been studied. Their density, molar volume, glass transition temperature and infrared spectroscopy have been investigated. The evolution of infrared spectra with the different constituents is studied and the oxide-forming character of TiO2 is discussed. In sodium titanophosphate glasses, the structures consist of distorted Ti octahedra linked to metaphosphate and pyrophosphate units through P-O-Ti bonds. The metaphosphate (P2O62-) and pyrophosphate (P2O74-) units coexist. Metaphosphate groups are the predominant structural units in glasses with the lowest TiO2 content. For TiO2-rich glasses, the pyrophosphate groups become the predominant structural units. A structural model is proposed to explain the experimental results. According to this model TiO2 is assumed to be present as six coordinated octahedral [TiO6/2](2-) units, again with shared corners. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 18]