Fig. 4. Pairwise reactions in the Y–Ba–Cu–O chemical space, illustrated by a heatmap where the color of each square represents the temperature (°C) at which a reaction is observed.

Inert pairs correspond to phases that do not react within the temperature range considered. White squares (unshaded) represent pairs of phases whose reactivity was not learned by ARROWS³. Yellow stars denote pairs that react to produce YBa₂Cu₃O_6.5 (YBCO). Orange circles and red crosses denote pairs that form impurities, Y₂BaCuO₅ and BaCuO₂, respectively.