Peculiarity of copper oxides


Copper oxides are unusual in two respects. First, octahedral-site CuII:t6e3 contains a single e hole in the 3d shell, which makes it orbitally degenerate and, therefore, a strong Jahn–Teller ion; consequently, CuII ions normally occupy square coplanar, pyramidal, or octahedral sites that are deformed to tetragonal (c/a > 1) symmetry by Jahn–Teller orbital ordering. However, without a cooperativity stabilizing long-range orbital ordering, the electrons may couple locally to E-mode vibrations, forming vibronic states in a dynamic Jahn–Teller coupling. Second, the CuII:3d9 energy level lies below the top of the O2 −:2p6 valence band in an ionic model; the introduction of covalent bonding creates states of e-orbital symmetry at the top of the O2 −:2p6 bands that have a large O-2pσ component (see Figure 26). Locally this O-2pσ component increases dramatically on oxidation of CuII to CuIII. The change in orbital mixing represents a polarization of the oxygen atoms that decreases the equilibrium Cu-O bond length. Still, the change in polarization is fast relative to the motion of the oxygen nucleus. Therefore, a dynamic vibronic phenomenon may reflect coupling to the polarization cloud of the oxygen atoms rather than to significant oxygen-atom displacements. Nevertheless, hybridizing an atomic vibration wave with a polarization wave on the oxygen-atom array would significantly increase an itinerant electron's effective mass m*. The copper-oxide superconductors all contain CuO2 sheets in which any apical Cu-O bonds perpendicular to a sheet are significantly longer than the in-plane Cu-O bonds. This structural feature signals full occupancy of the (3z2–r2) orbitals of an e-orbital pair. If you are looking for high quality, high purity, and cost-effective Copper oxide, or if you require the latest price, please email contact mis-asia.

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