Phase A was discovered using an iterative diffraction-chemical analysis route marked in green in Figure : EDX analysis of the sample that contained the unknown phase guided the selection of composition for further synthetic exploration. This step was repeated until the highest yield of the new material was achieved. It was not possible to grow suitable single crystals, so the polycrystalline sample that contained the highest phase fraction of the unknown Phase A (corresponding to a nominal composition of Ba16Y50Ru4Si29O157) was studied by means of different diffraction techniques. Continuous rotation electron diffraction enabled analysis of particles which were otherwise too small for single crystal X-ray diffraction , and its combination with consecutive energy dispersive X-ray spectroscopy (EDX) analysis enabled identification of particles with the symmetry and composition of the new phase. The SPXRD and neutron TOF studies were combined to provide the widest range of diffraction information for the polycrystalline sample. A combination of these techniques resulted in structure solution and refinement of the composition as Ba5Y13[SiO4]8O8.5. The final synthesis of the sample with this nominal composition provided the highest purity sample. The composition of new Phase A is located away from the initial BaRuO3-Y2Ru2O7-Y2Si2O7 boundary and the final product contained no ruthenium in the structure, as confirmed by chemical analysis. Details on the samples, their compositions and analysis are given in SI2.