Dopping generally influences the cell parameters. First of all, you have to be specific on the doping material. For example, if you are going to dop a metal ion into a bimetallic system to convert it into a trimetallic system then choose a metal ion (to be doped) with less or bigger atomic radius to which it will replace into the lattice. This will help to determine the change in the unit cell parameters along with the unit cell volume w.r.t. the mother composition. This I can suggest from my point of view.