  High-entropy oxides (HEOs) are a new class of materials that are promising
for a wide range of applications. Designing HEOs needs to consider both
geometric compatibility and electrical equilibrium. However, there is currently
no available method to systematically consider these two factors when selecting
constituent materials for making HEOs. Here we propose a two-step strategy,
where a HEO system to be explored is first partitioned into multiple subsystems
based on the valence combinations of substituted cations; the geometric
compatibility is then considered in selecting suitable substituted cations. We
demonstrate this strategy by using A(5B0.2)O3 perovskite as a model system. We
show that the system can be partitioned into 12 subsystems. Ten of the
subsystems have formed a single-phase cubic perovskite, while two have
partially ordering structure. The formation of single phases is correlated to
Goldschmidt's tolerance factor, while the formation of the ordering structure
is mainly correlated to cation-valence difference. We anticipate that this
strategy is applicable to exploring HEOs in other systems.
