Assessing Thermodynamic Selectivity of Solid-State Reactions for the Predictive Synthesis of Inorganic Materials

Synthesis is a major
challenge in the discovery of new inorganic
materials. Currently, there is limited theoretical guidance for identifying
optimal solid-state synthesis procedures. We introduce two selectivity
metrics, primary and secondary competition, to assess the favorability
of target/impurity phase formation in solid-state reactions. We used
these metrics to analyze 3520 solid-state reactions in the literature,
ranking existing approaches to popular target materials. Additionally,
we implemented these metrics in a data-driven synthesis planning workflow
and demonstrated its application in the synthesis of barium titanate
(BaTiO3). Using an 18-element chemical reaction network
with first-principles thermodynamic data from the Materials Project,
we identified 82985 possible BaTiO3 synthesis reactions
and selected 9 for experimental testing. Characterization of reaction
pathways via synchrotron powder X-ray diffraction reveals that our
selectivity metrics correlate with observed target/impurity formation.
We discovered two efficient reactions using unconventional precursors
(BaS/BaCl2 and Na2TiO3) that produce
BaTiO3 faster and with fewer impurities than conventional
methods, highlighting the importance of considering complex chemistries
with additional elements during precursor selection. Our framework
provides a foundation for predictive inorganic synthesis, facilitating
the optimization of existing recipes and the discovery of new materials,
including those not easily attainable with conventional precursors.