Structure of aqueous ammonium calcium nitrate glass former studied by neutron diffraction

A neutron diffraction experiment was carried out on the glass-forming aqueous system of ammonium calcium nitrate tetrahydrate, ACN (NH4NO3. Ca(NO3)(2). 4H(2)O). The method of isotopic substitution was used to determine the local structure round the NO3- ion, the hydrogen-hydrogen (g(HH)(r)), the hydrogen-oxygen (g(OH)(r)), and the nitrogen-hydrogen (g(N2H)(r)) radial pair distribution functions, in both the glassy (153 K) and liquid (303 K) states. The results show that significant changes occur on glassification. In particular, the nitrate ion exhibits an increase in the number of close hydrogen contacts and enhancement of its local structure. A microstructural model is proposed to explain the strong glass-forming ability of ACN.