The experimental route that led to discovery of Phase B is highlighted in blue in Figure . During the exploration of the BaRuO3-Y2Ru2O7-Y2Si2O7 phase field, a newly-developed tool Probabilistic Isolation of Crystalline Inorganic Phases (PICIP) was tested for the first time on two of the first powder samples that presented the unidentified peaks in their diffraction patterns (Figure , a). A detailed description of how PICIP works is provided in the SI (page 3), however, as input, PICIP takes the nominal overall compositions for each sample, and the relative amounts of known crystalline phases present in that sample as estimated from quantitative X-ray diffraction-based phase analysis. PICIP assumes uncertainties in these relative amounts of known phases and predicts a probability density over a region of phase space evaluating the expected average composition of the unknown phases present. This probability density can be aggregated over multiple samples with different nominal compositions to improve the overall accuracy, effectively triangulating the average composition of the unknown phases. PICIP thus automates application of the lever rule in high-dimensional chemical space taking experimental uncertainties into account, in order to accelerate identification of compositions affording unknown structures. PXRD analysis of samples 1 and 2 revealed mixtures of the known phases Y2Ru2O7 and Ba9Y2[SiO4]6 (details in Table ) along with reflections from the unknown phases. On the basis of the relative amounts of Y2Ru2O7 and Ba9Y2[SiO4]6 in these samples and using a standard deviation of 2 wt% on these amounts, PICIP predicted the residual composition to be in a different region of the Ba-Y-Si-Ru-O chemical space compared to Phase A suggesting the presence of an additional unknown phase (Figure ). It should be noted that EDX analysis of sample 2 showed two points in the same region but they did not cluster as well as for phase A (Figure ). From the aggregated probability density an additional four compositions were chosen by PICIP (Samples 11-14, Figure ) and prepared using the same synthetic routine as for the initial batch (details are given in SI1). The PXRD patterns of these samples revealed a second set of unidentified reflections. The presence of other crystalline phases as well as amorphous phases in the region close to Phase B prevented the definitive use of EDX analysis as was used for Phase A to determine the subsequent points for synthesis (see Figure ). Here it should be noted that some of the studied samples became completely amorphous upon melting if annealed for too long at 1573 K (see Figure for sample 13, Ba15Y5Ru2Si18O61). This happened for Ru-deficient and Si-rich compositions, and agrees with the previous reports for the BaO-Y2O3-SiO2 system, where a wide range of compositions in the SiO2-rich corner form amorphous glasses upon melting. Incorporation of small quantities of ruthenium (IV) oxide into the glass also hindered estimation of the composition of the new crystalline phase. Therefore, PICIP was used again starting with the relative amounts of known phases BaSiO3, Ba9Y2[SiO4]6 and BaRuO3 in sample 13 (Table , Figure ) with a 2 wt% standard deviation on these amounts to suggest the next compositions for experimental synthesis. Since any amorphous phases present will not contribute to the relative amount of known crystalline phases in the sample, their composition will also contribute to the average composition of unknown phases in the sample. Whilst this prevents PICIP from suggesting compositions which have a reduced amount of amorphous phase, PICIP remains able to suggest compositions which minimise the amount of competing known crystalline phases. Integration of PICIP in the exploratory routine helped obtain a sample with a high yield of Phase B with respect to crystalline phases, which was finally sufficient for CRED/EDX studies. Final tuning of the composition and reaction conditions resulted in a sample with the highest purity of Phase B as determined by X-ray diffraction (starting composition of Ba31Y23Si46O157.5, annealing at 1573 K for 12h). This composition yields an almost phase-pure powder of Phase B with respect to the crystalline phases present (detailed synthetic procedure is described in SI1). At the same time, it does contain a noticeable amount of amorphous glassy phase. TEM imaging helped to identify the presence of two different particle morphologies, sometimes in the same crystallite, corresponding to Phase B and an amorphous phase (Figure ). Similarly to phase A, no ruthenium was necessary for the formation of this phase.