Novel bonding concepts for superconductive oxides: An XPS study

Abstract

Detailed analyses of the x‐ray photoelectron spectra (XPS), of the normal (above Tc) phase for the Ba‐Y‐Cu‐oxide (1‐2‐3) superconductors, their precursors, and related systems have revealed a number of interrelated patterns, particularly that of the singular O(1s) peak (at 528.5±0.3 eV) apparently produced by most, if not all, of these superconductive systems. This result (and its corresponding O(2s) value) has been shown to correspond closely to those oxygen binding energies produced by BaO and Y2O3, but not by any of the copper oxides. This suggests that the 1‐2‐3 systems are substantially influenced by the extreme ionic fields induced by the barium (and yttrium) ions, whereas the copper in these systems is, in larger part, a structural cohabitant in the extremely ionic Cu3O−77−x ions. The latter ions are shown to produce key electronic results that are quite different from those induced by the copper in the aforementioned copper oxides. The primary characteristics of that difference are suggested to be the substantial shifts and contractions experienced in the O(2p) part of the resulting valence band. In the case of BaO, its (O(2p) dominated) valence band is pushed quite close to its pseudo‐Fermi (zero binding energy) edge. In fact, we predict a separation of only about 1 to 2 eV. Interjection of copper (into the 1‐2‐3 system) results in a substantial Cu(3d) band, that we suggest ‘‘double’’ perturbs the O(2p) band of the superconductors. Part of the latter band is pushed to higher binding energy (enhanced covalency), whereas the other side of the O(2p) band is shifted downfield to a point of contact with the Fermi edge. This, in our model, the origin of superconductivity is the mirror image of that proposed by most previous researchers.Detailed analyses of the x‐ray photoelectron spectra (XPS), of the normal (above Tc) phase for the Ba‐Y‐Cu‐oxide (1‐2‐3) superconductors, their precursors, and related systems have revealed a number of interrelated patterns, particularly that of the singular O(1s) peak (at 528.5±0.3 eV) apparently produced by most, if not all, of these superconductive systems. This result (and its corresponding O(2s) value) has been shown to correspond closely to those oxygen binding energies produced by BaO and Y2O3, but not by any of the copper oxides. This suggests that the 1‐2‐3 systems are substantially influenced by the extreme ionic fields induced by the barium (and yttrium) ions, whereas the copper in these systems is, in larger part, a structural cohabitant in the extremely ionic Cu3O−77−x ions. The latter ions are shown to produce key electronic results that are quite different from those induced by the copper in the aforementioned copper oxides. The primary characteristics of that difference are suggested to be...