Superconductive ceramics properties

Gabovich, A.M., Moiseev, D.P. and Shpigel , A.S., Anomalous Behavior of the Thermodynamic Properties of the Superconducting Ceramic BaPbj xBixOs. Sov. Phys. Solid State 24(6) 1071 (1982). 

The new superconducting ceramics offer a way out, if they can be made in some workable form, probably a thin film, and so long as the circuits can be operated at around 80° K or higher. The oxides could then be used on the circuit chips themselves to connect transistors and other devices and to make connections between chips. There is also the possibility that the superconducting properties in the new materials can be manipulated by, say, moving oxygen in and out as needed, or that the ceramics will turn out for some reason to be more suitable than conventional superconducting materials for use in transistors. 

The discovery of the new high Tc, superconducting ceramics has generated excitement among physicists and material scientists alike. It is important to recognize that these materials are very similar to other advanced ceramics in that they are prepared from oxide powders which are pressed and sintered. They are polycrystalline materials whose electrical, magnetic, and mechanical properties will be critically dependent on their... 

In summary, the picture of these superconducting ceramics at this time is one which shows an extremely complex relationship between the various properties and the processing conditions. It is clear that almost every property measured, i.e. magnetic,... 

Future efforts at ANL will be aimed at completing the specification of the necessary processing parameters and in measuring the mechanical properties of such superconducting ceramics. 

Ceramics have followed a similar course, beginning with the ancient Mesopotamians who used bricks and made brick buildings. Cement, concrete, and to some extent glass have similarly been used largely for their mechanical properties. Paralleling the broadening of the uses of metals, however, ceramics have also over the last two centuries developed many uses not related to their mechanical properties. These include ceramic insulators, piezoelectric ceramics, solar cells, zeolite catalysts, and most recently the superconducting ceramics. 

Ceramics are formed from silicates found in the soil. Artists use them to create pottery, but engineers and scientists have created ceramics with superconductive properties. Investigate the growing field of superconductive ceramics. 

There are presently four famihes of high-temperature superconductors under investigation for practical magnet appheations. Table 11-25 shows that all HTS are copper oxide ceramics even though the oxygen content may vary. However, this variation generally has little effect on the phvsical properties of importance to superconductivity. 

The properties of these brittle ceramics depend critically on the preparative conditions. Intimate mixtures of the oxides, carbonates or nitrates of the relevant metals in the required proportions are heated at temperatures of 900-I000°C. For YBa2Cu307 j , all compositions in the range 0 < jc < 0.5 superconduct and the highest Tc is found where jc 0. For others, the oxygen content must be stringently controlled. In all cases, the most... 

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. 

After more than ten years of extensive experimental and theoretical studies of the phenomenon of the high Tc superconductivity (HTSC) [1], we still do not know a microscopic mechanism responsible for this phenomenon. Numerous theories of pairing, which lead to high Tc values, are based on models [2-9] and cannot connect a specific chemical composition of HTSC ceramics with the value of the transition temperature Tc. For creating a quantitative theory of the HTSC phenomenon further comparative studies of the electronic structure and their relative properties of SC and non-SC ceramics are needed. In this paper, we confine ourselves to calculations of the electronic structure of the SC yttrium ceramics. 

The amount and positions (atomic locations) of oxygen atoms in the superconductors are highly critical and determine the properties of the superconductor. The oxygen vacancies (or deficiency) can be ordered in these materials. Neutron-diffraction experiments were required to determine the population parameters and the atomic positions of oxygen in these structures. The superconducting transition temperature in these "ceramic" oxides is a critical balance between the oxygen content and a proper mix of Cu2+ and Cus+ ions generated in the anneal or post-heat treatment. 

It should be clear from the above sections that the idealized formula Bi2Sr2Can iCun02n+4 with n = 1, 2, and 3 does not accurately describe the actual stoichiometry of single-phase ceramic samples. Substantial cation intersite substitution and/or vacancies probably occur in these materials. The role of these defects in the stabilization of the superconducting phases and their contribution to the superconducting properties is still being investigated. 

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