Short- and medium-range structures of cerium aluminophosphate glasses: A molecular dynamics study

Properties of rare earth aluminophosphate glasses depend profoundly on the local coordination environments and the distribution of rare earth ions, as well as the glass-forming network structures that accommodate these rare earth ions. In this paper, we have studied the structure of a series of cerium aluminophosphate glasses with both Ce3+ and Ce4+ oxidation states using larger classical molecular dynamics (MD) simulations (with over 13,000 atoms) for a wide range of cerium oxide concentrations (1.8-23.8 mol%). The simulated structure models were validated by comparing with the structure factor and correlation function from high energy X-ray diffraction studies. The short- and medium-range structure characteristics of these glasses as a function of composition have been obtained. P5+ ions are found to be fourfold coordinated and their local structure remains unchanged in the entire series while the coordination environments around Al3+, Ce3+, and Ce4+ ions show composition dependence. Aluminum ions are mainly four-coordinated with considerable increase of five-coordinated with increasing alumina content. Cerium distribution was analyzed by clustering analysis, [CeOx] polyhedra connectivity analyses, and Ce-Ce pair distribution functions. It was found that relatively high cerium oxide concentration (similar to 14 mol%) can be incorporated in the glasses while maintaining the desired cerium ion distribution. With higher cerium content, cerium cluster formation is inevitable and characterized by increasing cluster size by the formation of direct Ce-O-Ce linkages. (C) 2014 Elsevier B.V. All rights reserved.