On the stereochemistry of cations in the doping block of superconducting copper oxides

Metal-oxygen complexes containing Cu, Tl, Hg, Bi, and Pb cations are electronically active in superconducting copper oxides by stabilizing single phases with enhancedT _c, whereas other metal-oxygen complexes deteriorate copper oxide superconductivity. Cu. Tl, Hg, Bi, and Pb in their actual oxidation states are closed-shelld ¹⁰ or inerts ² pair ions. Their electronic configurations have a strong tendency to polarize the oxygen environment. The closed shelld ions with low-lyingnd ¹⁰nd ⁹(n+1)s excitations form linear complexes through hybridization polarizing the apical oxygens. Comparatively lownd ⁹(n+1)s excitation energies distinguish Cu^1+,3+, Tl³⁺, Hg²⁺, from other closed-shelld ¹⁰ ions deteriorating copper oxide superconductivity, e.g., Zn²⁺.