Crystal Chemical Aspects and Substitutions in High T sub c Cuprates

Superconductivity in the cuprates is induced by introducing "holes" or "electrons" into compounds which contain formally divalent copper. This is frequently done by substitution of heterovalent ions for the non-copper metals. Examples are (La,Ba)CuO sub 4 and (Nd, Ce) sub 2 Cu O sub 4. Alternatively, the oxygen content is varied, as in Ba sub 2 YCu sub 3 O sub x, or oxygen is substituted by fluorine, as in Nd sub 2 Cu(O,F) sub 4.