From Online Dictionary of Crystallography

Diadochie (Fr). Diadochie (Ge). Diaochia (It). ディアドヒー (Ja). Diadoquía (Sp).

Diadochy is the capability of an atom to replace another in a particular crystal structure. The degree of substitution depends on the physical conditions (temperature and pressure) as well as the atomic size, charge, and electronic structure of the diadochic partners.