| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 4699006 | Chemical Geology | 2013 | 11 Pages |
The structural environment around Y in silicate and aluminosilicate glasses containing 5000 ppm Y was investigated as a function of melt composition and polymerization using Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. The used glass compositions were taken from Prowatke and Klemme (2005) varying in the aluminum saturation index (ASI, molar ratio of Al2O3/(Na2O + K2O + CaO)) from 0.115 to 0.768. Furthermore, a set of glass compositions from the system CaO–Al2O3–SiO2 (CAS) was used, for which structural data from computer simulations are available (Haigis et al., 2013--this issue). Structural parameters of the Y–O pair correlation of the first coordination shell were determined from the EXAFS based on a gamma-like distribution function that accounts for the large static disorder and non-Gaussian pair distributions. The analysis shows an increase in the coordination number from 6 to 8, along with an increase of the average Y–O distance by 0.13 Å for the composition of Prowatke and Klemme (2005). For the CAS-composition an increase of the coordination number from 6 to 7, along with an increase of the average Y–O distance by 0.06 Å is obtained. The change of these parameters is associated with a considerable increase in the asymmetry and width of the Y–O pair distribution. Due to its size and charge, 6-fold coordinated Y will preferentially bond to non-bridging oxygens of the polymeric melt network to form a stable configuration, as is the case for the less polymerized melts with low ASI. In highly polymerized melts with ASI values close to one, 6-fold coordination of Y is not possible because almost only bridging oxygens are available. Consequently, over-bonding of bridging oxygens around Y is counterbalanced by an increase of coordination number and Y–O distance to satisfy local charge balance requirements.
► Local structure environment of Y in aluminosilicate glasses as a function of polymerization. ► Procedure to derive reliable structural parameters for REE in quenched melts by EXAFS. ► Increase of asymmetry of PDF around Y is correlated with increasing polymerization. ► Increase of the Dcrystal/melt of Y is correlated with increasing asymmetry of PDF around Y. ► Local structure in less polymerized melts is energetically more favorable for Y.
