Based Cuprates

Preparation of Bismuth- and Thallium-Based Cuprate Superconductors... 

The layer-type structures and chemical nature of the constituents of the bismuth and thallium-based cuprate superconductors - notably the lone-pair stereochemistry of Bis+, variable valence of copper, and considerable exchange among some of the cation sites - combine to make structural non-ideality, nonstoichiometry, and phase intergrowth the rule rather that the exception in these families of materials. These features, as well as the probable metastability of the phases (and possibly all high-temperature oxide superconductors), also contribute to the difficulties typically encountered in preparing single-phase samples with reproducible properties and compositions. 

The primary difficulty in preparing the thallium-based cuprate superconductors lies in the toxicity and volatility of the reactant Tl2Os and its decomposition products. Above 600°C, the following redox-vaporization process is well under way and would lead to substantial loss of reactant in an open system, although the... 

The following sections will outline specific methods for the synthesis of Bi- and Tl-based cuprate superconductors. Because the synthetic methods and historical evolution of the compounds are different, the bismuth and thallium families are described separately. 

Table 1. Crystallographic data are presented for the new phases which resulted from a 3d-metal substitution at the copper site in the n=l, 2 and 3 Bi-based cuprates. The periodicity of the structural modulation (p) is given by bold numbers when obtained from single crystal x-ray studies, otherwise the values were obtained from TEM studies. 

From the study of cationic substitutions in the La, Y, and Bi-based cuprates a large amount of data has been obtained that we now try to systematize in order to develop the most prominent trends. 

The discovery of high-temperature superconductivity in a lanthanum-based cuprate perovskite material with a transition temperature of Tc = 35 K by Bednorz and Muller... 

One of main thrusts in organic-perovskite hybrids has been in the preparation of stable delaminated perovskite sols as the building blocks of nanocomposite materials. A well-known process for exfoliation is to weaken the attractive interaction of the layers through intercalation of bulky organic components. A representative example is exfoliation of bismuth-based cuprate superconductors (Figure 14.12). °3... 

Since the discovery of high temperature superconductivity (T > 30 K) in the La-Ba-Cu-O system hundreds of high temperature superconducting oxides have been found, with the record Tc of 164 K in Hg-1223 under high pressure. According to their major chemical difference, these superconductors can be classified into six major categories K2Nip4-type cuprates, rare-earth-based cuprates, bismuth-based cuprates, thallium-based cuprates, mercury-based cuprates, and other cuprates. Details of every superconductor are not presented, but at least one typical composition of each major type will be discussed in detail. Interested readers can read the relevant literature to get specific information on other systems. 

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