Which parameters are necessary for a substitutional solid solution?

The formation of a substitutional solid solution requires specific conditions related to the size and structure of the constituent atoms. Compatibility in atomic radii is crucial; when the difference between the atomic radii of the substituting elements is within 15%, it allows for easier incorporation of one element in the structure of another without causing significant distortion.

Additionally, having compatible crystal structures ensures that the host material can accommodate the substituting atoms without creating extensive lattice strain. If the crystal structures are not compatible, the substitution may lead to instability or immiscibility rather than a uniform solid solution. This structural compatibility is vital for maintaining the integrity of the material and allowing for uniform properties within the solution.

In summary, the correct choice emphasizes that a small size difference, alongside compatible crystal structures, enables the successful formation of substitutional solid solutions, where one element can substitute for another in the lattice of a crystalline solid.