In the absence of significant short-ranged dopantdefect interactions, aliovalent doping can be modelled as a perturbation to the electroneutrality condition (eq. ( )). where M is an aliovalent dopant with relative charge r and fixed concentration [M r ] [21]. In the dilute limit, this doping response does not depend explicitly on the dopant species and insertion site, but only on the product r[M r ].