The Ba/Y disorder that is not resolved even in the lower symmetry P21 model could be a driving force for the further splitting of the disilicate groups. The network formed by these disilicate groups in the unit cell of Ba3Y2[Si2O7]2 is shown in Figure . Each of the 4 mixed Ba/Y sites has a non-equivalent coordination to 4 split disilicate groups. Since the mixed sites represent the statistical possibility of the presence of different atomic species, the split disilicate groups model the possibility of having a lower coordination number environment for yttrium atoms and a larger one for barium (corresponding to their ionic radii). Despite the high degree of disorder, such a model gives us a glimpse of the possible local ordering of the atomic species. As exemplified for the mixed site M1 in Figure , b, it can be realized either as the larger 10-coordinated environment typical for barium or a smaller 6-coordinated yttrium. Similar decomposition into two different environments for M2-M4 sites is shown in Figure . These arrangements of disilicate groups representing coordination to two cation environments show possibilities of local ordering within the structure of Ba3Y2[Si2O7]2. Since there are four split Ba/Y sites and 8 pairs of disilicate groups, one is presented with 32 different options (2 4 +2 4 ) to populate the unit cell in an orderly manner. Therefore, we must assume that this model corresponds to the average structure of Ba3Y2[Si2O7]2 and drawing an exact connectivity pattern between Ba/Y and each set of split disilicate groups is beyond the scope of this study. The disorder correlates well with observed physical behaviour of phase B which turns into a glass upon melting. Hence this model is an example of a crystalline structure on the way to become amorphous.