Molecular dynamics simulations of P2O5-Fe2O3-FeO-Na2O glasses

Phosphate glasses due to their properties can be used in many fields like medicine, optics, electronics, environmental protection etc. Unfortunately, pure phosphate glasses have low chemical durability what limits their application. The addition of iron to the glass improves the durability considerably. Glass with composition 60P(2)O(5)-40Fe(2)O(3) have one of the highest chemical resistance. The glass properties are strongly related to the structure of the glass network which can be tested experimentally and also by application of computer simulations. In the paper classical molecular dynamics simulations were used to study the influence of the gradual addition of Na2O on the structure of 55P(2)O(5)-30Fe(2)O(3)-15FeO glass. Increasing sodium content in the glass causes depolymerization of the glass network and increasing number of non-bridging oxygens in [PO4] tetrahedra. The number of chemical durable P-O-Fe bridges decreases and they are replaced by P-O-Na. This leads to separation of iron cations from [PO4] units and formation of iron oxides clusters. The network of the glass with over 30 mol % of Na2O consists mainly of separated [PO4] tetrahedra and short pyrophosphate chains of [P2O7](4-). The glass structural properties due to sodium content increase are discussed.