On the Stereochemistry of the Cations in the Doping Block of Superconducting Copper-Oxides

Abstract

Metal-oxygen complexes containing Cu,- Tl-, Hg-, Bi- and Pb-cations are electronically active in superconducting copper-oxides by stabilizing single phases with enhanced $T_c$, whereas other metal-oxygen complexes deteriorate copper-oxide superconductivity. Cu, Tl, Hg, Bi, Pb in their actual oxidation states are closed shell $d^{10}$ or inert $s^2$ pair ions. Their electronic configurations have a strong tendency to polarize the oxygen environment. The closed shell $d$ ions with low lying $n{d}^{10}\leftrightarrow n{d}^9(n+1)s$ excitations form linear complexes through $d_{z^2}-s$ hybridization polarizing the apical oxygens. Comparatively low $n{d}^9(n+1)s$ excitation energies distinguish $\mathrm{C}{\mathrm{u}}^{1+,3+},\mathrm{T}{\mathrm{l}}^{3+},\mathrm{H}{\mathrm{g}}^{2+}$ from other closed shell $d^{10}$ ions deteriorating copper-oxide superconductivity, {\it e.g.} $\mathrm{Z}{\mathrm{n}}^{2+}$.

arXiv comment5 pages, uses REVTEX. To be published in: J. Superconductivity, Proc. Int. Workshop on "Phase Separation, Electronic Inhomogenities and Related Mechanisms for High T_c Superconductors", Erice (Sicily) 9-15 July 1995

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