Structure of K₂O–TeO₂ Glasses

Abstract

The structure at room temperature and structural change from room temperature to the temperature above melting point (T m ) of K2O-TeO2 glasses were studied by the use of XAFS spectroscopy, high-temperature Raman spectroscopy, high-temperature XRD and X-ray RDF (Radial Distribution Function). XAFS spectroscopy has indicated that K2O-TeO2 glasses consist of both TeO4 trigonal bipyramid (tbp) units and TeO3 trigonal pyramid (tp) units , and high-temperature Raman results have indicated that TeO4 tbp units convert to TeO3 tp units with the increase of temperature and by the addition of K2O in the K2O-TeO2 glasses. The high-temperature XRD and X-ray RDF results were in good agreement with the results of the high-temperature Raman spectroscopy. Furthermore, the XAFS spectroscopy has shown that potassium ions have a similar local structure in all K2O-TeO2 glasses studied.

Alkali environments in tellurite glasses

“…This value is much smaller than the value of 6 concluded on the basis of EXAFS and X-ray diffraction [7], or the assumed value of 7 used in a combined neutron and X-ray diffraction study [5]. Furthermore, the average nKO in crystalline K2Te4O9 is 6.5 [21], and therefore a value ~2 is not reasonable.…”

“…For the potassium tellurite glasses (K10 and K20), has a more intense peak at ~2.8 Å than for the corresponding Li and Na glasses, and this can be attributed to K-O bonds. Conversely, the Li20 glass has a less intense peak at ~1.9 Å than the K20 and Na19 glasses (Figure 4b), due to the presence of Li-O bonds (the coherent neutron scattering length of 7 Li is negative, -2.22 fm [37], and hence the Li-O contribution to is negative).…”

“…The lithium (Li20) and potassium (K10 and K20) tellurite glasses were made at Osaka Prefecture University, as described previously [7]. The potassium tellurites were made using K2CO3 and TeO2 as precursors and the lithium tellurite glass was made using enriched 7 Li2CO3.…”

“…It was concluded that the 5-coordinated environment is more representative of the glass, based on the results of the previous 23 Na NMR study [11]. An Extended X-ray Absorption Fine Structure (EXAFS) and X-ray diffraction (XRD) study of two potassium tellurite glasses [7] indicated that the K-O coordination number, nKO, is 6, with K-O bond lengths of 2.71 Å. However, a second study, using neutron and X-ray diffraction to investigate three potassium tellurite glasses, determined that the K-O contribution to the results was too small to allow the coordination to be determined.…”

“…The local structure of alkali M2O-TeO2 glasses (M = Li, Na, and K) has been studied extensively using neutron diffraction [1][2][3][4][5], X-ray diffraction [6,7], EXAFS [7,8], Raman scattering [7,9,10], NMR [2,[11][12][13] and RMC modelling [2,14]. In these studies, particular emphasis was placed on determining the local environment of tellurium and there is a general consensus that the average tellurium coordination number, nTeO, decreases as an oxide modifier is added to the glass network, the change being driven by the bonding requirements of the modifier.…”