Structure of Ca0.4K0.6(NO3)1.4 from the glass to the liquid state

We have investigated the structure of a model fragile glass former Ca_0.4K_0.6(NO₃)_1.4(CKN) by using neutron and x-ray diffraction and reverse Monte Carlo modeling in a temperature range covering the glass transition. The results show that the structure of the glass phase contains, in addition to short-range charge ordering, intermediate-range ordering that is due to fluctuation of nitrate ion concentration in the range 3-15 Å. Furthermore, the nitrate ions are orientationally correlated and form chainlike substructures. Gradual changes of the structure factor were observed in the Q range 1-5 Å^-1 on passing through the glass transition temperature, which can partly be attributed to changes in density. However, the orientational correlation between the planar NO^-₃ ions present in the glass phase is lost in the liquid phase.