Cu-O chains

Figure 5.2 Oxygen states present at the ends of -Cu-O-Cu-O- chains are established as the active sites in ammonia oxidation at Cu(110) from a Monte Carlo simulation of the growth of the oxygen adlayer. The reactivity (the experimental curve) is best fitted to the atoms present at chain ends. (Reproduced from Ref. 7).

Figure 3 Orthorhombic structures of YBa2Cus07 (left) containing single Cu-O chains between the copper-oxygen sheets, and YBa2 Cu4Og (right) with double Cu-O chains between the copper-oxygen sheets. Metal atoms are shaded and Cu-O bonds are shown. The c axis is vertical, and the Cu-O chains run along the b axis direction which is oriented in and out of the plane of the drawing.

Torardi et al, 1987 David et al, 1987). The structure is closely related to that of the superconducting copper oxide YBa2Cu307, consisting of square-pyramidally coordinated copper (Cu-O sheets) and square-planar copper (Cu-O chains). Excess oxygen in the lanthanum compound is located interstitially converting partially the chain copper to square-pyramidal and/or octahedral coordination. 

Figure 7.17 Structures of YBa2Cuj07, Bi2CaSr2Cu20g and Tl2CaBa2Cu20g. Notice the presence of the CUO2 sheets (containing CuO, square-pyramids) and of the Cu-0 chains in YBa2Cu307- In YBa2Cu40g there are two Cu-O chains in the unit cell compared to one in YBa2Cu307.

A breakthrough in superconductor technology came with the discovery24 of yttrium barium copper oxide, YBa2Cu307, whose crystal structure is shown here. When heated, the material readily loses oxygen atoms from the Cu-O chains, and any composition between YBa2Cu307 and YBa2Cu3Ob is observable. 

Structure of YBa2Cu307. reproduced from G. F. Holland and A. M. Stacy, Physical Properties of the Quaternary Oxide Superconductor YBa2Cu3Ox, Acc. Chem. Res. 1988, 21, 8. One-dimensional Cu-O chains (shown in color) run along the crystallographic t>-axis, and two-dimensional Cu-O sheets lie in the a-b plane. Loss of colored oxygen atoms from the chains at elevated temperature results in YBa2Cu306. 

Figure 2 Structures of YBa2Cu307, Bi2CaSr2Cu20 and Tl2CaBa2Cu20 . Notice the presence of Cu02 sheets containing CuO 3 square-pyramids. Additionally, there are Cu—O chains in YBa2Cu207.

Fig. 8.5. Electron energy loss spectra of Ca2Cu03 along the Cu—O chain and out of it.

For the 1-2-3 materials, the O Is spectrum is narrower than for the 2-1-4 s. It is made up of a dominant component at -529 eV derived from Cu-O planes (accounting for 4 of 7 oxygen atoms in a formula unit) and a shallower component that we attribute to Cu-O chains (accounting for the remainder oxygen atoms). Again, we identify the... 

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