Influence of CaO on structural features of polyphosphate P2O5-Fe2O3-FeO glasses by molecular dynamics simulations

Abstract

Phosphate glasses can be used in many applications fields like medicine, optoelectronics, environmental protection, etc. Their properties are strongly dependent on the glass network structure. The paper presents classical molecular dynamics simulations studies of the influence of the gradual addition of CaO on structural features of 55P2O5-30Fe2O3-15FeO glass. The base glass is built of different lengths chains and rings which are being shortened due to CaO addition. Thus, the glass network depolymerization takes place. The phosphate network is joined by iron-oxygen polyhedrons which increase polymerization of the network. The increase of non-network oxygen ions is observed what can be related to the rising of Ca and Fe ions aggregation. The aggregation of calcium is the most dominant at the low concentration of this oxide. The effect leads to the observation of the glass network non-homogeneity. The increase of the CaO concentration causes expansion of the Ca-rich regions which finally extend over the entire glass network for the CaO content above 45%. Above this point, the phosphate network is mostly composed of isolated Q0 structural units. The P-O-P bridges are broken more easily than P-O-Fe due to an increase in the modifier content.