High-temperature structure of K2O-TeO2 glasses

The structural change of K2O-TeO2 glasses (xK(2)O:TeO4, x:5, 10, 15, 20, 25 and 30 mol%) from room temperature to a temperature higher than the melting point (T-m) was studied by the use of Raman spectroscopy, XRD (X-ray diffraction), X-ray RDF (radial distribution function) and XAFS (X-ray absorption fine structure) spectroscopy. The Raman results indicated that TeO4 trigonal bipyramid (tbp) units convert to TeO3 trigonal pyramid (tp) units with increasing temperature and by the addition of K2O to the K2O-TeO2 glasses. We found that a 10K(2)O.90TeO(2) (mol%) glass mainly consists of TeO4 tbp unit, while 20K(2)O.80TeO(2) (mol%) and 30K(2)O.90TeO(2) (mol%) glasses are composed of the mixture of TeO4 tbp and TeO3 tp units. The high-temperature XRD and X-ray RDF results are in agreement with the results of high-temperature Raman spectroscopy. Furthermore, the XAFS spectroscopy shows that potassium ions have a similar local structure in all of the K2O-TeO2 glasses studied. (C) 1999 Elsevier Science B.V. All rights reserved.