Q: "A graduate student tells you that he has observed a Schottky defect in a sample of pure aluminium. Explain why it may take a long time for this graduate student to get his Ph.D" A: "Pure aluminium has no negatively charged particles, so a Schottky effect can not occur." So I know a Schottky effect is when both an anion (-) and a cation (+) dissappear together out of a material (both because it has to remain neutral). What I don't understand is why aluminium does not have negatively charged particles. It does have electrons so no I'm just not following here.. Can anyone explain this to me?