Non-Stoichiometry & Partial Occupancies Explained

[tirrel]

Hello, I'd like to understand better the relation between non-stoichiometry and partial occupancies. Let's suppose for example that after an Xray analysys I find that in a material a site can be occupied by an atom of type 1 or an atom of type 2 with 50 % probability. Does it usually mean that the material is non stoichiometric and that it is possible to produce a material with different stechiometric ratios or there is no relation?

 

[Bystander]

after an Xray analysys I find that in a material a site can be occupied by an atom of type 1 or an atom of type 2 with 50 % probability

Can you rephrase this? It's not making any sense to me in terms of stoichiometry. Are you talking about lattice defects when you say "sites?"