We performed molecular dynamics (MD) simulations of the structure and properties of cerium-containing phosphosilicate, aluminophosphate, and aluminophosphosilicate glasses based on recent spectroscopic data that revealed 95% of cerium ions in such glasses are Ce 31 . New Ce 31 -and Ce 41 -O 2À potentials were developed and used in the MD simulations of these ceriumcontaining glasses with mixed glass formers. The local environments around cerium ions and network-forming cations, the medium range structure including glass-forming network Q n distribution, clustering, and second coordination shell around cerium ions have been carefully characterized. The results showed a longer Ce-O bond length and larger coordination number for Ce 31 than Ce 41 (2.48 and 6.4 vs. 2.24Å and 5.8, respectively). Around 5% of Si 41 ions were found to be in fivefold and sixfold coordination states in cerium phosphosilicate glasses, rather than the usual fourfold in silicate glasses. At the same time, the silicon-oxygen polyhedra were highly polymerized (over 80% of Q 4 ) due to the presence of phosphorus oxide. Aluminum ions were found to be coordinated by four-, five-, and six oxygen ions, with an average coordination number of around 4.2. In both oxidation states, cerium ions were found to be preferentially surrounded by phosphorus-oxygen tetrahedra, which form a kind of solvation shell around them. The preference of network-forming cations around cerium ions in the second coordination shell was found to decrease in the sequence phosphorus, aluminum, silicon.
The local structure of cerium in two systematic compositional series of glasses, nominally CeP 3 O 9 -AlP 3 O 9 and CeP 3 O 9 -SiP 2 O 7 , was interrogated using X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) spectroscopy. XPS revealed that, for glasses melted in air, ! 95% of cerium ions are Ce 3+ . This was independently confirmed using X-ray absorption near edge spectroscopy (XANES). Ce K-edge extended X-ray absorption fine structure (EXAFS) has been used to determine the local structure of Ce 3+ . Near the metaphosphate composition, cerium was found to have an average cerium coordination number of~7.0 and an average cerium-oxygen bond length of 2.41 Å . The average cerium coordination number and average cerium-oxygen bond distance were found to increase with decreasing cerium concentration in both compositional series. Rare-earth clustering is suggested based on numerical calculations for glasses containing ! 14 and ! 15 mol% Ce 2 O 3 for the aluminophosphate and silicophosphate series, respectively. II. BackgroundTwo compositional series, centered on cerium metaphosphate, Ce 2 O 3 ·3P 2 O 5 , were chosen to investigate cerium incorporation L.-Q. Chen-contributing editor Manuscript No. 28744.
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