A molecular dynamics study of the atomic structure of (CaO)x(Al2O3)1-x glass with x=0.625 close to the eutectic

Aluminate glasses are difficult to prepare as they do not contain traditional network formers, but they are promising materials for optical applications. The atomic structure of calcium aluminate glasses has been studied using several experimental techniques. The current study uses molecular dynamics to obtain a model of a (CaO)(0.625)(Al2O3)(0.375) glass close to the eutectic. The glass consists of a tetrahedral alumina network with average network polymerization < Q(n)> of n = 3.3. Ca acts as a network modifier with average coordination of 6.2. Ca is typically coordinated to three bridging oxygens (O-b) and three non-bridging oxygens (O-nb), with Ca-O-nb bonds noticeably shorter than the Ca-O-b bonds. A new method of analysing modifier cation coordination is presented, which specifically shows the distribution of Ca coordination N-CaO in terms of combinations of N-CaOb and N-CaOnb. O-b is most often coordinated to two Al plus two Ca, and Onb is most often coordinated to one Al plus three Ca. The typical coordinations of Ca, O-b, and O-nb all have a noticeable similarity to those for the 5CaO center dot 3Al(2)O(3) crystal. The Ca-Ca distribution shows a clear similarity to that for (CaO)(0.5)(SiO2)(0.5) glass, and this is attributed to the equal atomic number densities of Ca in these glasses.