Composition
selection and crystal-growth control are the most important
issues in material development. Crystal growth using a molten salt
as the solvent, which is otherwise known as the flux method, is expected
to be one of the key technologies for developing crystalline materials,
because this method can grow single crystals of inorganic materials
with control of the crystal habit and size. In the flux method, the
number of combinations of experimental conditions usually exceeds
10,000 owing to the wide variety of experimental variables, such as
solvents and heating conditions. Due to such large combinations, the
conventional trial-and-error approach based on hypothesis testing
would take several years to obtain the optimal crystal, and the crystal
control region is also limited. As a result, the development of crystalline
materials is risky, and their use is limited. To overcome this issue,
we propose a novel crystal growth approach called flux-method process
informatics (FPI). The FPI approach generates a data-driven experimental
proposal based on machine learning predictions. More specifically,
regression analyses are carried out using the experimental process
as the explanatory variable and the crystal shape/size as the objective
variable. In this study, FPI was applied to the layered perovskite-type
oxide Ba5Nb4O15. It was found that
the experimental efficiency of the FPI approach was five times higher
than that of humans, and it was able to quantitatively control the
shape of low-aspect-ratio crystals, which is usually difficult for
anisotropic structures. These achievements provide new insights into
the rapid development of high-performance crystalline materials.