On the stereochemistry of 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 Tc, whereas other metaloxygen 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 ↔ 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 Cu 1+,3+ , Tl 3+ , Hg 2+ from other closed shell d 10 ions deteriorating copper-oxide superconductivity, e.g. Zn

Novel octahedral tilt system a + b + c + in (1 − x)Na0.5Bi0.5TiO3–xCdTiO3 solid solutions

“…It is evident that Cd 2+ is responsible for the quite extraordinary square planar coordination in NBT containing solid solutions. Formation of structures with a low coordination number is characteristic feature of closed-shell d 10 ions and results from d-s and d-s-p hybrid orbitals [27].…”

Understanding the depolarization phenomena in (1−x) Na0.5Bi0.5TiO3. (x) Ba0.85Ca0.15Ti0.90Zr0.10O3 solid solutions using in-situ temperature dependent Raman spectroscopy

“…The repulsive force exerted by these lone pairs on other bonding arrangements affects the spatial distribution of bonding electron pairs, leading to an asymmetrical local coordination environment. Consequently, this induces a non-centrosymmetric and polar crystal structure, thereby enhancing physical properties, notably piezoelectricity and ferroelectricity [19,20]. The work by Schutz et al discussed that the mechanism at T d is neither displacive nor order-disorder but is mediated by the loss of Bi 3+ and O 2− hybridization due to thermal vibration along the polar axis [21].…”