Copper and oxygen atoms

The key to the superconducting properties of these ceramics seems to be the presence of planes of copper and oxygen atoms bonded to one another. The significance of the other atoms in the lattice seems to be to provide a stmctural framework for the copper and oxygen atoms. Thus, in the superconducting compound YBa2Cu30, the substitution of other rare earths for yttrium resrrlts in little change in the properties of the material. 

Ceramic oxide superconductors have distinct atomic layers. The Cu-containing superconductors contain planes of copper and oxygen atoms, as the molecular view shows. These planes alternate with layers containing oxygen and the other metals that make up the superconductor. Superconductivity takes place in the Cu—O planes. 

Challenges to Established Theories, It is interesting to note that some theoreticians struggle with describing how superconductivity occurs at high temperatures in the newer, ceramic superconductors. This is understandable because the classic theory of superconductivity is tied to metals. Most ceranuc superconductors discovered to date incorporate distinctive layers of copper and oxygen atoms, One question posed by some researchers, Is the mechanism of high-temperature superconductivity the same in hole superconductors as it is in electron superconductors ... 

Figure 1. Copper/oxygen layer of Superconducting cuprates. Black and white circles represent copper and oxygen atoms respectively. A pair of E-basis Wannier functions, which are a linear combination of Cu and O atomic orbitals, transforming as (x, y) are localised on every lattice point at the centre of the unit cell.

Figure 12 Arrangement of copper and oxygen atoms in a Cu02 plane of the conduction layer (from Ref 13, p. 99)...

The structure of Cu(acac)2 was determined by XRD. The metal-oxygen distance of about 1.93 A is considerably shorter than 2.01 A for [Ni(acac)2]3 , 2.02 A for Ni(acac)2 2H20, 2.03 A for Zn(acac)2 H20 and 2.05 A for Co(acac)2 2H20. This contraction is attributed to the smaller repulsion between the copper and oxygen atoms in the tetracoordinate square-planar strucmre than in the hexacoordinate octahedron. 

In January 1986, Bednorz was working alone in his lab with his latest mix. Instead of just combining the powdery oxides, as the French team had done, he dissolved them in water, allowed the particles to settle, then fired them at around 1,800° F. What he came up with was a sandwich consisting of layers of lanthanum and barium atoms alternating with layers of copper and oxygen atoms. 

The chains Brodsky speaks of are one-dimensional, alternating linkups of copper and oxygen atoms that form the latticework of the ceramic crystal, a sequence that many... 

Even though the yttrium and barium (and any of the other elements that show up in the various mixes) are important—they donate electrons for Cooper pairing and may simply act as glue to hold the structure together—it is the copper-oxygen bond that seems to form the hot wire of this rig. Since the distances between the copper and oxygen atoms in the layers are not great, electron transfer, and thus the flow of electric current between them, occurs fairly easily. 

SUPERCHAINS AND PLANES. The atomic structure of ceramic superconductors contains chains and planes of copper and oxygen atoms. Both chains and planes appear to contribute to high-temperature superconductivity in some of the new materials. (Courtesy Argonne National Laboratory.)... 

It soon became apparent, once the structure of the yttrium compound was bared, that either or both of two central features might account for superconductivity at those record-high temperatures. One was the puckered, two-dimensional plane of copper and oxygen atoms ilar to the flat plane seen earlier in the structure of another superconductor, made of lanthanum, strontium, and copper oxide, that became superconducting at around 40° K. The other was unexpected the one-dimensional chain of copper and oxygen atoms, a sequence unknown in earlier superconductors. The challenge was fairly clear to both theorists and experimentalists. Were the planes or the chains responsible for superconductivity above 90° K ... 

Figure 1. Coordination polyhedra of copper and oxygen atoms in high Tc superconductors (a) square planar, (b) pyramidal (4+1) and (c) distorted octahedron (4+2). The distance x is about 1.95A and the distance y about 2.3A.

High temperature superconductors are ceramic materials consisting of complex ionic oxides that become superconducting when cooled by liquid nitrogen. That is, they lose all resistance to electrical current. One example is the material YBa2Cu30y which crystalhzes to form sheets of copper and oxygen atoms that can carry electrical current in the planes of the sheets. 

Fig. 9 DFT-based modeling of decoherence within a bio-inspired model of the active site on mononuclear copper enzymes. Top, two complexes investigated presenting an N3 or an N2S coordination sphere. Bottom., diverging motion of the copper and oxygen atoms on the fs timescale for one set of diverging trajectories. The transparent spheres represent the mass-dependent wave packet of each nucleus. Color code. Cu in brown, O in red, N in blue, C in green, S in yellow, and H in white...

In the case of our present interest we find in both complexes that the decay of the nuclear wave packet overlap is almost completely due to the diverging motion of the copper and oxygen atoms. The curves Jcu02 closely follow the product of the curves for both complexes (Figure 5.8). The omission of the... 

Almost all HTSCs are hard, brittle ceramic oxides that have sheets of copper and oxygen atoms sandwiched between layers of either cations or a combination of cations and oxide ions, and all are derived from their respective parent insulators by doping. 

In the addendum for this chapter, the contribution to antiferromagnetism that arises from the overlap between the nearest-neighbour copper and oxygen atomic orbitals is discussed. 

To date, many of the ceramic superconductors contain copper and share a common structural feature copper and oxygen atoms bonded together in planar sheets. In YBCO superconductors, the Cu—O planes are widely separated. In bismuth superconductors, the Cu—O planes occur in "sandwiches" consisting of two closely spaced sheets separated by a layer of group 2 ions. These sandwiches are separated from one another by several layers of bismuth oxide. In the thallium superconductors, the Cu—O planes are stacked in groups of three, like triple-decker sandwiches. 

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