Structure of Cerium Phosphate Glasses: Molecular Dynamics Simulation

Abstract

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 3+ . New Ce 3+ ‐ and Ce 4+ ‐O 2− potentials were developed and used in the MD simulations of these cerium‐containing 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 3+ than Ce 4+ (2.48 and 6.4 vs. 2.24Å and 5.8, respectively). Around 5% of Si 4+ 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.