Attempts to solve the structure directly from CRED data were made using direct methods, intrinsic phasing and charge flipping algorithms implemented in Olex2. Every attempt failed, which can be attributed to low intensity of some reflections which could not be extracted by REDp or micro ED CrysAlisPro v43. Nevertheless, electron diffraction provided us with a crucial insight into the structure of Ba3Y2[Si2O7]2. Upon a careful re-examination of different sections of the 3D reciprocal space of the CRED data, violations of the 00l = 4n and 0k0 = 2n reflection conditions of the P43212 space group were observed (Figure ). At the same time, clear systematic absences were observed along the h00 axis. To satisfy these reflection conditions, the symmetry of the model was lowered from P43212 to its direct subgroup of P21 (Figure ). Comparison between the calculated patterns in both symmetries is given in Figure , b, and is in a good agreement with the experimental data (Figure and). The group-subgroup relationship and the atomic parameters evolution is illustrated in Figures (oxygen atoms are omitted). The monoclinic model in the P21 space group was successfully refined using combined SPXRD and TOF neutron diffraction data (a = 16.47640(4), b = 9.04150(5), c = 9.04114(7) Å, β = 90.0122(9)°), and its accuracy was evaluated using the maximum entropy method (MEM). The refined SPXRD and TOF banks 5 and 2 patterns are shown on the right-hand side of Figure (the featured background of the neutron diffraction spectra is caused by a presence of the amorphous phase). All profiles for Banks 6-2 are shown in Figure .