Cuprate superconductor

CUO2 layers appear in all cuprate superconductors and appear to be a necessary but not sufficient condition for high temperature superconduction. The La2SrCu20g 2 compound has CUO2 layers but does not superconduct. Experiments also indicate that T is proportional to the carrier density in the CUO2 layer but not to the volume carrier density, which is further evidence that the YBa2Cu202 is a two-dimensional superconductor. 

Among the high-temperature superconductors one finds various cuprates (i.e., ternary oxides of copper and barium) having a layered structure of the perovskite type, as well as more complicated oxides on the basis of copper oxide which also include oxides of yttrium, calcium, strontium, bismuth, thallium, and/or other metals. Today, all these oxide systems are studied closely by a variety of specialists, including physicists, chemists, physical chemists, and theoreticians attempting to elucidate the essence of this phenomenon. Studies of electrochemical aspects contribute markedly to progress in HTSCs. 

Karpfen A (2007) Theoretical Characterization of the Trends in Halogen Bonding. 126 1-15 Keller H (2005) Unconventional Isotope Effects in Cuprate Superconductors 114 143-169 Keller H, see Bussmann-Holder A (2005) 114 367-386 Khan AI, see Williams GR (2005) 119 161-192... 

Muller KA (2005) Essential Heterogeneities in Hole-Doped Cuprate Superconductors 114 1-11... 

The superconducting oxides include both perovskites and Ruddlesden-Popper compounds which have an orthorhombic arrangement of cubic cells, alternatively of the perovskite and sodium chloride structures. The common feature of all of these is the presence of copper as a major component. The first ceramic superconductor was a lanthanum-strontium substituted cuprate (Lai Sr Cu04 z), which is a perovskite, but subsequently the inter-oxide compound Y203 2BaO 3CuO, commonly referred to as a 123 compound, was shown to have superior performance. The speculation concerning the conduction mechanism is that this involves either Cu3+-Cu2+ positive hole... 

For e > 0.1,there is a possibility to adjust e to the recent experimental data on k(T) (Brandstatter,1994) for high — Tc cuprate superconductor TI2CC12(7 — 2223). Our calculations show that,the best choice of e is found to be e = 0.21.The appropriate k(t) is presented in Fig.4 (solid line). The dashed line in this figure shows k(t) for D = 3. This fitting process allows us to get an estimation on the effective dimensionality of the high — Tc superconducting materials. 

Apart from structures that are built of slabs, modular structures that can be constructed of columns in a jigsawlike assembly are well known. In the complex chemistry of the cuprate superconductors and related inorganic oxides, series of structures that are described as tubular, stairlike, and so on have been characterized. Alloy structures that are built of columns of intersecting structures are also well known. Structures built of linked columns, tunnels, and intersecting slabs are also found in minerals. Only one of these more complex structure types will be described, the niobium oxide block structures, chosen as they played a significant role in the history of nonstoichiometry. 

CUPRATE HIGH-TEMPERATURE SUPERCONDUCTORS 8.6.1 Perovskite-Related Structures and Series... 

The important and widely studied copper-oxide-derived high-temperature superconductors, known as cuprate superconductors, are basically insulators. Doping converts these into metallic materials, many of which are superconductors over rather more restricted composition ranges. Several of these materials have already been discussed La2Cu04 and Sr2Cu02F2 (Section 4.3.3), La2 A.SrxCu04 (Section 8.5.1), and Nd2, Ce,Cu04 (Section 8.5.2). 

In these and the other cuprate superconductors, the part of the structure that leads to superconductivity is the slab of Cu02 sheets. When more than one sheet is present, they are separated by cation layers, Q (usually Ca or Y) to give a sequence Cu02-(Q-Cu02) i, which forms the superconducting layer in the material. The index n is the total number of Cu02 layers in the phase, which is equal to the formula number of Cu atoms present (Fig. 8.5). 

Figure 8.5 Superconducting planes found in cuprate superconductors (a) a single Cu02 sheet and (b) a Cu02 (Q — Cu02) i superconducting layer.

Figure 8.6 Schematic depiction of a cuprate superconductor. Doping into the charge reservoir layers results in the transfer of holes to the superconducting layers.

Figure 8.9 Simplified generic phase diagram for cuprate superconductors.

Twin boundaries are frequently encountered in cuprate superconductors. There are a number of ways in which twins might form in a crystal, one of which is... 

The charge reservoir layer in the cuprate superconductor HgBa2CaCu206+s is ... 

Cuprammonium rayon, 11 263—265 Cuprate oxides, 23 838-839 Cuprate superconductors, 23 837 Cupric bromide, physical properties of,... 

The structures of ternary oxides such as spinels, perovskites, pyrochlores, layered cuprates (high-7 c superconductors), and other lamellar oxides are fascinating subjects by themselves and are beyond the scope of the present discussion. 

Tcr cuprates), whose superconductivity depends on subtle, phonon-free coupling between electrons. It is interesting that the highest known temperature Type-I superconductor, MgB2, shows a much larger isotope effect than does mercury (TCr (MgnB2) = 39.2 K, TCr (Mg10B2) = 40.2 K). 

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