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

A neutron diffraction experiment was carried out on the glass-forming aqueo us system of ammonium calcium nitrate tetrahydrate, ACN (NH4NO3. Ca(NO3)(2) . 4H(2)O). The method of isotopic substitution was used to determine the lo cal structure round the NO3- ion, the hydrogen-hydrogen (g(HH)(r)), the hyd rogen-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) state s. The results show that significant changes occur on glassification. In pa rticular, the nitrate ion exhibits an increase in the number of close hydro gen contacts and enhancement of its local structure. A microstructural mode l is proposed to explain the strong glass-forming ability of ACN.