Discovery of Unconventional Proton-Conducting Inorganic Solids via Defect-Chemistry-Trained, Interpretable Machine Learning

High-throughput computational screening and machine learning hold significant potential for exploring diverse chemical compositions and discovering novel inorganic solids. However, the complexity of point defects, which occur in all inorganic solids and are often crucial to their functionality and synthesizability, presents significant challenges. Here, this study presents a defect-chemistry-trained, interpretable machine learning approach, designed to accelerate the exploration and discovery of unconventional proton-conducting inorganic solid electrolytes. By considering dopant dissolution and hydration reactions, the machine learning models provide quantitative predictions and physical interpretations for synthesizable host–dopant combinations with hydration capabilities across various structures. Utilizing these insights, two unconventional proton conductors, Pb-doped Bi₁₂SiO₂₀ sillenite and eulytite-type Sr-doped Bi₄Ge₃O₁₂, are discovered in the first two synthesis trials. Notably, the Pb-doped Bi₁₂SiO₂₀ represents an unprecedented class of proton-conducting electrolyte composed solely of groups 14 and 15 cations and featuring a sillenite structure. It exhibits unique and fast 3D proton conduction along a loosely bonded BiO₅ network. This study demonstrates an efficient approach for exploring novel inorganic materials.