mixed crystal (solid solution)

https://doi.org/10.1351/goldbook.M03940
A crystal containing a second constituent which fits into and is distributed in the lattice of the host crystal. (The use of 'solid solution' for amorphous materials is not recommended.)
Source:
Orange Book, 2nd ed., p. 85 (https://media.iupac.org/publications/analytical_compendium/)