Crystallographic defect
= Crystallographic defect
{wiki}
A <crystallographic defect> is a departure from ideal repeated structure. In an <ionic crystal>, a missing <ion> can provide an available site for another <ion> to move into; movement still requires overcoming an <activation energy>. This is why an ideal immobile-site model is a limit rather than a universal law for <solid> <electrical conductivity>.<Chemistry 2e>[§10.5, “Crystal Defects”: vacancies and other imperfections]{ref}