How to define defects or foreign elements in custom crystal orientation?

Dear Experts,

After reading the development toolkit book about the definition of materials, I find that G4 can use G4CrystalExtension and G4LogicalCrystalVolume to define crystalline structure. If I want to define a kind of complex crystal , how to add defects or foreign elements such as Fe3+ and S to the crystal? If I use low energy PHOTON to hit the crystal from <100> and <110> orientation, does G4 have ability to track the evolution of the defects?

Looking forward to your reply sincerely
Runsheng Zheng