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

TL;DR

This paper investigates how the electronic configurations of metal cations in copper-oxide superconductors influence their ability to stabilize superconducting phases, highlighting the role of specific cation states and their electronic excitations.

Contribution

It provides a detailed analysis of the stereochemistry and electronic interactions of metal cations in the doping block of copper-oxides, elucidating their impact on superconductivity.

Findings

Cu, Tl, Hg, Bi, Pb stabilize superconductivity in copper-oxides.

Certain closed shell d ions with low excitation energies deteriorate superconductivity.

Electronic polarization of oxygen environment is key to phase stabilization.

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 $nd^{10}\leftrightarrow nd^9(n+1)s$ excitations form linear complexes through $d_{z^2}-s$ hybridization polarizing the apical oxygens. Comparatively low $nd^9(n+1)s$ excitation energies distinguish $\rm Cu^{1+,3+}, Tl^{3+}, Hg^{2+}$ from other closed shell $d^{10}$ ions deteriorating copper-oxide superconductivity, {\it e.g.} $\rm Zn^{2+}$.