High-Tc Compounds

Key words Theories and Models of the Superconducting State Type II Superconductivity High-Tc Compounds... 

As mentioned recent experiments under pressure succeeded in the observation of SdH oscillations in the isostructural high-Tc compounds... 

We report and compare different synthesis techniques for the preparation of the high Tc compound YBa2Cu307 y and conclude that sol-gel is very promising because dense and homogeneous ceramics with transitions as sharp as 0.5K are obtained. This technique is not specific to the yttrium compound, but can be used to make homogeneous chemical substitutions. 

It is well known that for all Cu—O high Tc compounds, the electrical conductivity is much higher within the ab plane than out of it. For example, by... 

Due to the magnetic field there is also an off-diagonal thermal Hall conductivity Kxy which has been identified in high-Tc compounds (Ocana and Esquinazi, 2002). The fom-fold oscil-... 

The high-Tc compound YBa2Cu3(>7 j crystallizes in the orthorhombic space group Pmmm (No. 47) with Ti 91K for 0 < 3 < 0.2 (Table 4.2-17). The superconducting properties depend on the oxygen content 7 — 5. Oxygen loss on the e site [0(1) in YBa2Cu307] leads to a destruction of the Cu—O chains. For 3=1 only linear coordinated Cu(l) atoms are present. 

This appendix summarizes some basic aspects of the theory of superconductivity, covering the classical London equations, the BCS theory of weakly coupled low-Tc materials, the unconventional superconductivity of strongly coupled high-Tc compounds with its electronic and magnetic origin, and contributes some aspects to the understanding of the behavior of type II superconductors. 

The electron density in transition metal complexes is of unusual interest. The chemistry of transition metal compounds is of relevance for catalysis, for solid-state properties, and for a large number of key biological processes. The importance of transition-metal-based materials needs no further mention after the discovery of the high-Tc superconducting cuprates, the properties of which depend critically on the electronic structure in the CuOz planes. 

Paul" Chu, and others at University of Houston, also reproduced Zurich s I.B.M. research results (156). Bell Lab s confirmation of Bednorz and Muller s discovery of high Tc superconductivity in copper oxide compounds was published (157) in the Jan. 1987 issue of Physical Review Letters. The electrical resistivity data from their work showing an onset of superconductivity at 36.5 K for the composition Lax gSr0 2Cu04 is plotted as Figure 28. This product also showed a 60-70% Meissner effect. 

Tables 1 through 7 giving positional and isotropic thermal parameters for most of the compounds discussed in this chapter. These data are taken, for the most part, from the literature, but, for a few materials that have not been structurally characterized, calculated positions are given. The tables also include lattice constants, space groups, and compositional data. Table 8 gives calculated x-ray powder diffraction information (26 (Cu), d-spacing, hkl, and intensity) for the same oxide compounds. In regard to the diffraction patterns, it should be remembered that preferred orientation and absorption effects, and cation substitutions will make the experimentally observed intensities differ from the calculated ones. Additional information on the crystal structures of high-Tc oxides can be found in a recent review (48).

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