A molecular dynamics model of the atomic structure of dysprosium alumino-phosphateglass

Abstract

Molecular dynamics (MD) has been used to identify the relative distribution of dysprosium in the phosphateglass DyAl0.30P3.05O9.62. The MD model has been compared directly with experimental data obtained fromneutron diffraction to enable a detailed comparison beyond the total structure factor level.The MD simulation gives correlations at 3.80(5) and 6.40(5) Å with relative coordination numbers of 0.8(1)and 7.3(5), thus providing evidence of minority rare-earth clustering withinthese glasses. The nearest neighbour Dy–O peak occurs at 2.30 Å with eachDy atom having on average 5.8 nearest neighbour oxygen atoms. The MDsimulation is consistent with the phosphate network model based on interlinkedPO4 tetrahedra where the addition of network modifiersDy3+ depolymerizes the phosphate network through the breakage of P–(O)–P bonds whilstleaving the tetrahedral units intact. The role of aluminium within the network has beentaken into explicit account, and Al is found to be predominantly (78%) tetrahedrallycoordinated. In fact all four Al bonds are found to be to P (via an oxygen atom) withnegligible amounts of Al–O–Dy bonds present. This provides an important insight intothe role of Al additives in improving the mechanical properties of these glasses.