Final answer:
Option (c) 'a single missing positive ion and an interstitial positive ion' cannot occur in an ionic ceramic since it would violate the charge balance needed in the crystal structure, while options (a) and (b) can occur as substitutional impurities.
Step-by-step explanation:
The question is asking which of the following defects cannot occur in an ionic ceramic: a) substitutional impurity cation, b) substitutional impurity anion, c) a single missing positive ion and an interstitial positive ion, or d) all of the above. When we consider the nature of ionic ceramics and their crystalline structure, we can evaluate the presence of different types of crystal defects.
Point defects can be seen within ionic crystals. Two common defects are Frenkel and Schottky defects. Frenkel defects involve misplacement of ions, leading to interstitial ions and vacancies but maintaining charge balance within the crystal. Schottky defects involve coupled vacancies of both cations and anions while also maintaining electrical neutrality in the ionic solid.
Substitutional impurity cations and anions are also possible when an impurity atom occupies a normal lattice site. However, the combination of a single missing positive ion and an interstitial positive ion (c) would disrupt the charge balance, which is not a characteristic defect for ionic ceramics, as any point defects would usually occur in such a way to maintain charge neutrality.
Thus, option (c) 'a single missing positive ion and an interstitial positive ion' is a defect that cannot occur in an ionic ceramic since it would violate the requirement for charge balance in the crystal structure. Options a) and b) can indeed occur as they can be compensated for by other mechanisms that maintain the overall charge balance of the crystal.